1.. _todo:
  2
  3=========
  4TODO list
  5=========
  6
  7This section contains a list of smaller janitorial tasks in the kernel DRM
  8graphics subsystem useful as newbie projects. Or for slow rainy days.
  9
 10Difficulty
 11----------
 12
 13To make it easier task are categorized into different levels:
 14
 15Starter: Good tasks to get started with the DRM subsystem.
 16
 17Intermediate: Tasks which need some experience with working in the DRM
 18subsystem, or some specific GPU/display graphics knowledge. For debugging issue
 19it's good to have the relevant hardware (or a virtual driver set up) available
 20for testing.
 21
 22Advanced: Tricky tasks that need fairly good understanding of the DRM subsystem
 23and graphics topics. Generally need the relevant hardware for development and
 24testing.
 25
 26Expert: Only attempt these if you've successfully completed some tricky
 27refactorings already and are an expert in the specific area
 28
 29Subsystem-wide refactorings
 30===========================
 31
 32Remove custom dumb_map_offset implementations
 33---------------------------------------------
 34
 35All GEM based drivers should be using drm_gem_create_mmap_offset() instead.
 36Audit each individual driver, make sure it'll work with the generic
 37implementation (there's lots of outdated locking leftovers in various
 38implementations), and then remove it.
 39
 40Contact: Simona Vetter, respective driver maintainers
 41
 42Level: Intermediate
 43
 44Convert existing KMS drivers to atomic modesetting
 45--------------------------------------------------
 46
 473.19 has the atomic modeset interfaces and helpers, so drivers can now be
 48converted over. Modern compositors like Wayland or Surfaceflinger on Android
 49really want an atomic modeset interface, so this is all about the bright
 50future.
 51
 52There is a conversion guide for atomic [1]_ and all you need is a GPU for a
 53non-converted driver.  The "Atomic mode setting design overview" series [2]_
 54[3]_ at LWN.net can also be helpful.
 55
 56As part of this drivers also need to convert to universal plane (which means
 57exposing primary & cursor as proper plane objects). But that's much easier to
 58do by directly using the new atomic helper driver callbacks.
 59
 60  .. [1] https://blog.ffwll.ch/2014/11/atomic-modeset-support-for-kms-drivers.html
 61  .. [2] https://lwn.net/Articles/653071/
 62  .. [3] https://lwn.net/Articles/653466/
 63
 64Contact: Simona Vetter, respective driver maintainers
 65
 66Level: Advanced
 67
 68Clean up the clipped coordination confusion around planes
 69---------------------------------------------------------
 70
 71We have a helper to get this right with drm_plane_helper_check_update(), but
 72it's not consistently used. This should be fixed, preferably in the atomic
 73helpers (and drivers then moved over to clipped coordinates). Probably the
 74helper should also be moved from drm_plane_helper.c to the atomic helpers, to
 75avoid confusion - the other helpers in that file are all deprecated legacy
 76helpers.
 77
 78Contact: Ville Syrjälä, Simona Vetter, driver maintainers
 79
 80Level: Advanced
 81
 82Improve plane atomic_check helpers
 83----------------------------------
 84
 85Aside from the clipped coordinates right above there's a few suboptimal things
 86with the current helpers:
 87
 88- drm_plane_helper_funcs->atomic_check gets called for enabled or disabled
 89  planes. At best this seems to confuse drivers, worst it means they blow up
 90  when the plane is disabled without the CRTC. The only special handling is
 91  resetting values in the plane state structures, which instead should be moved
 92  into the drm_plane_funcs->atomic_duplicate_state functions.
 93
 94- Once that's done, helpers could stop calling ->atomic_check for disabled
 95  planes.
 96
 97- Then we could go through all the drivers and remove the more-or-less confused
 98  checks for plane_state->fb and plane_state->crtc.
 99
100Contact: Simona Vetter
101
102Level: Advanced
103
104Convert early atomic drivers to async commit helpers
105----------------------------------------------------
106
107For the first year the atomic modeset helpers didn't support asynchronous /
108nonblocking commits, and every driver had to hand-roll them. This is fixed
109now, but there's still a pile of existing drivers that easily could be
110converted over to the new infrastructure.
111
112One issue with the helpers is that they require that drivers handle completion
113events for atomic commits correctly. But fixing these bugs is good anyway.
114
115Somewhat related is the legacy_cursor_update hack, which should be replaced with
116the new atomic_async_check/commit functionality in the helpers in drivers that
117still look at that flag.
118
119Contact: Simona Vetter, respective driver maintainers
120
121Level: Advanced
122
123Rename drm_atomic_state
124-----------------------
125
126The KMS framework uses two slightly different definitions for the ``state``
127concept. For a given object (plane, CRTC, encoder, etc., so
128``drm_$OBJECT_state``), the state is the entire state of that object. However,
129at the device level, ``drm_atomic_state`` refers to a state update for a
130limited number of objects.
131
132The state isn't the entire device state, but only the full state of some
133objects in that device. This is confusing to newcomers, and
134``drm_atomic_state`` should be renamed to something clearer like
135``drm_atomic_commit``.
136
137In addition to renaming the structure itself, it would also imply renaming some
138related functions (``drm_atomic_state_alloc``, ``drm_atomic_state_get``,
139``drm_atomic_state_put``, ``drm_atomic_state_init``,
140``__drm_atomic_state_free``, etc.).
141
142Contact: Maxime Ripard <mripard@kernel.org>
143
144Level: Advanced
145
146Fallout from atomic KMS
147-----------------------
148
149``drm_atomic_helper.c`` provides a batch of functions which implement legacy
150IOCTLs on top of the new atomic driver interface. Which is really nice for
151gradual conversion of drivers, but unfortunately the semantic mismatches are
152a bit too severe. So there's some follow-up work to adjust the function
153interfaces to fix these issues:
154
155* atomic needs the lock acquire context. At the moment that's passed around
156  implicitly with some horrible hacks, and it's also allocate with
157  ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
158  the acquire context explicitly on stack and then also pass it down into
159  drivers explicitly so that the legacy-on-atomic functions can use them.
160
161  Except for some driver code this is done. This task should be finished by
162  adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
163
164* A bunch of the vtable hooks are now in the wrong place: DRM has a split
165  between core vfunc tables (named ``drm_foo_funcs``), which are used to
166  implement the userspace ABI. And then there's the optional hooks for the
167  helper libraries (name ``drm_foo_helper_funcs``), which are purely for
168  internal use. Some of these hooks should be move from ``_funcs`` to
169  ``_helper_funcs`` since they are not part of the core ABI. There's a
170  ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
171
172Contact: Simona Vetter
173
174Level: Intermediate
175
176Get rid of dev->struct_mutex from GEM drivers
177---------------------------------------------
178
179``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
180everything. Nowadays in modern drivers the only bit where it's mandatory is
181serializing GEM buffer object destruction. Which unfortunately means drivers
182have to keep track of that lock and either call ``unreference`` or
183``unreference_locked`` depending upon context.
184
185Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
186and there's a GEM object ``free`` callback for any drivers which are
187entirely ``struct_mutex`` free.
188
189For drivers that need ``struct_mutex`` it should be replaced with a driver-
190private lock. The tricky part is the BO free functions, since those can't
191reliably take that lock any more. Instead state needs to be protected with
192suitable subordinate locks or some cleanup work pushed to a worker thread. For
193performance-critical drivers it might also be better to go with a more
194fine-grained per-buffer object and per-context lockings scheme. Currently only
195the ``msm`` and `i915` drivers use ``struct_mutex``.
196
197Contact: Simona Vetter, respective driver maintainers
198
199Level: Advanced
200
201Move Buffer Object Locking to dma_resv_lock()
202---------------------------------------------
203
204Many drivers have their own per-object locking scheme, usually using
205mutex_lock(). This causes all kinds of trouble for buffer sharing, since
206depending which driver is the exporter and importer, the locking hierarchy is
207reversed.
208
209To solve this we need one standard per-object locking mechanism, which is
210dma_resv_lock(). This lock needs to be called as the outermost lock, with all
211other driver specific per-object locks removed. The problem is that rolling out
212the actual change to the locking contract is a flag day, due to struct dma_buf
213buffer sharing.
214
215Level: Expert
216
217Convert logging to drm_* functions with drm_device parameter
218------------------------------------------------------------
219
220For drivers which could have multiple instances, it is necessary to
221differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
222don't do this, drivers used dev_info/warn/err to make this differentiation. We
223now have drm_* variants of the drm print functions, so we can start to convert
224those drivers back to using drm-formatted specific log messages.
225
226Before you start this conversion please contact the relevant maintainers to make
227sure your work will be merged - not everyone agrees that the DRM dmesg macros
228are better.
229
230Contact: Sean Paul, Maintainer of the driver you plan to convert
231
232Level: Starter
233
234Convert drivers to use simple modeset suspend/resume
235----------------------------------------------------
236
237Most drivers (except i915 and nouveau) that use
238drm_atomic_helper_suspend/resume() can probably be converted to use
239drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
240of the atomic suspend/resume code in older atomic modeset drivers.
241
242Contact: Maintainer of the driver you plan to convert
243
244Level: Intermediate
245
246Reimplement functions in drm_fbdev_fb_ops without fbdev
247-------------------------------------------------------
248
249A number of callback functions in drm_fbdev_fb_ops could benefit from
250being rewritten without dependencies on the fbdev module. Some of the
251helpers could further benefit from using struct iosys_map instead of
252raw pointers.
253
254Contact: Thomas Zimmermann <tzimmermann@suse.de>, Simona Vetter
255
256Level: Advanced
257
258Benchmark and optimize blitting and format-conversion function
259--------------------------------------------------------------
 
260
261Drawing to display memory quickly is crucial for many applications'
262performance.
263
264On at least x86-64, sys_imageblit() is significantly slower than
265cfb_imageblit(), even though both use the same blitting algorithm and
266the latter is written for I/O memory. It turns out that cfb_imageblit()
267uses movl instructions, while sys_imageblit apparently does not. This
268seems to be a problem with gcc's optimizer. DRM's format-conversion
269helpers might be subject to similar issues.
270
271Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion
272helpers. In cases that can be further optimized, maybe implement a different
273algorithm. For micro-optimizations, use movl/movq instructions explicitly.
274That might possibly require architecture-specific helpers (e.g., storel()
275storeq()).
276
277Contact: Thomas Zimmermann <tzimmermann@suse.de>
278
279Level: Intermediate
280
281drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup
282-----------------------------------------------------------------
283
284A lot more drivers could be switched over to the drm_gem_framebuffer helpers.
285Various hold-ups:
286
287- Need to switch over to the generic dirty tracking code using
288  drm_atomic_helper_dirtyfb first (e.g. qxl).
289
290- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb
291  setup code can't be deleted.
292
293- Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for
294  valid formats for atomic drivers.
 
 
 
295
296- Many drivers subclass drm_framebuffer, we'd need a embedding compatible
297  version of the varios drm_gem_fb_create functions. Maybe called
298  drm_gem_fb_create/_with_dirty/_with_funcs as needed.
299
300Contact: Simona Vetter
 
 
 
 
 
 
 
 
 
 
 
301
302Level: Intermediate
303
304Generic fbdev defio support
305---------------------------
306
307The defio support code in the fbdev core has some very specific requirements,
308which means drivers need to have a special framebuffer for fbdev. The main
309issue is that it uses some fields in struct page itself, which breaks shmem
310gem objects (and other things). To support defio, affected drivers require
311the use of a shadow buffer, which may add CPU and memory overhead.
312
313Possible solution would be to write our own defio mmap code in the drm fbdev
314emulation. It would need to fully wrap the existing mmap ops, forwarding
315everything after it has done the write-protect/mkwrite trickery:
316
317- In the drm_fbdev_fb_mmap helper, if we need defio, change the
318  default page prots to write-protected with something like this::
319
320      vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot);
321
322- Set the mkwrite and fsync callbacks with similar implementions to the core
323  fbdev defio stuff. These should all work on plain ptes, they don't actually
324  require a struct page.  uff. These should all work on plain ptes, they don't
325  actually require a struct page.
326
327- Track the dirty pages in a separate structure (bitfield with one bit per page
328  should work) to avoid clobbering struct page.
329
330Might be good to also have some igt testcases for this.
331
332Contact: Simona Vetter, Noralf Tronnes
333
334Level: Advanced
335
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
336connector register/unregister fixes
337-----------------------------------
338
339- For most connectors it's a no-op to call drm_connector_register/unregister
340  directly from driver code, drm_dev_register/unregister take care of this
341  already. We can remove all of them.
342
343- For dp drivers it's a bit more a mess, since we need the connector to be
344  registered when calling drm_dp_aux_register. Fix this by instead calling
345  drm_dp_aux_init, and moving the actual registering into a late_register
346  callback as recommended in the kerneldoc.
347
348Level: Intermediate
349
350Remove load/unload callbacks
351----------------------------
352
353The load/unload callbacks in struct &drm_driver are very much midlayers, plus
354for historical reasons they get the ordering wrong (and we can't fix that)
355between setting up the &drm_driver structure and calling drm_dev_register().
356
357- Rework drivers to no longer use the load/unload callbacks, directly coding the
358  load/unload sequence into the driver's probe function.
359
360- Once all drivers are converted, remove the load/unload callbacks.
 
361
362Contact: Simona Vetter
363
364Level: Intermediate
365
366Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi
367---------------------------------------------------------------
368
369Once EDID is parsed, the monitor HDMI support information is available through
370drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to
371retrieve the same information, which is less efficient.
372
373Audit each individual driver calling drm_detect_hdmi_monitor() and switch to
374drm_display_info.is_hdmi if applicable.
375
376Contact: Laurent Pinchart, respective driver maintainers
377
378Level: Intermediate
379
380Consolidate custom driver modeset properties
381--------------------------------------------
382
383Before atomic modeset took place, many drivers where creating their own
384properties. Among other things, atomic brought the requirement that custom,
385driver specific properties should not be used.
386
387For this task, we aim to introduce core helpers or reuse the existing ones
388if available:
389
390A quick, unconfirmed, examples list.
391
392Introduce core helpers:
393- audio (amdgpu, intel, gma500, radeon)
394- brightness, contrast, etc (armada, nouveau) - overlay only (?)
395- broadcast rgb (gma500, intel)
396- colorkey (armada, nouveau, rcar) - overlay only (?)
397- dither (amdgpu, nouveau, radeon) - varies across drivers
398- underscan family (amdgpu, radeon, nouveau)
399
400Already in core:
401- colorspace (sti)
402- tv format names, enhancements (gma500, intel)
403- tv overscan, margins, etc. (gma500, intel)
404- zorder (omapdrm) - same as zpos (?)
405
406
407Contact: Emil Velikov, respective driver maintainers
408
409Level: Intermediate
410
411Use struct iosys_map throughout codebase
412----------------------------------------
413
414Pointers to shared device memory are stored in struct iosys_map. Each
415instance knows whether it refers to system or I/O memory. Most of the DRM-wide
416interface have been converted to use struct iosys_map, but implementations
417often still use raw pointers.
418
419The task is to use struct iosys_map where it makes sense.
420
421* Memory managers should use struct iosys_map for dma-buf-imported buffers.
422* TTM might benefit from using struct iosys_map internally.
423* Framebuffer copying and blitting helpers should operate on struct iosys_map.
424
425Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Simona Vetter
426
427Level: Intermediate
428
429Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly
430--------------------------------------------------------------------------------------
431
432The values in struct drm_mode_config.{max_width,max_height} describe the
433maximum supported framebuffer size. It's the virtual screen size, but many
434drivers treat it like limitations of the physical resolution.
435
436The maximum width depends on the hardware's maximum scanline pitch. The
437maximum height depends on the amount of addressable video memory. Review all
438drivers to initialize the fields to the correct values.
439
440Contact: Thomas Zimmermann <tzimmermann@suse.de>
441
442Level: Intermediate
443
444Request memory regions in all drivers
445-------------------------------------
446
447Go through all drivers and add code to request the memory regions that the
448driver uses. This requires adding calls to request_mem_region(),
449pci_request_region() or similar functions. Use helpers for managed cleanup
450where possible.
451
452Drivers are pretty bad at doing this and there used to be conflicts among
453DRM and fbdev drivers. Still, it's the correct thing to do.
454
455Contact: Thomas Zimmermann <tzimmermann@suse.de>
456
457Level: Starter
458
459Remove driver dependencies on FB_DEVICE
460---------------------------------------
461
462A number of fbdev drivers provide attributes via sysfs and therefore depend
463on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make
464any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective
465code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not
466all drivers might be able to drop CONFIG_FB_DEVICE.
467
468Contact: Thomas Zimmermann <tzimmermann@suse.de>
469
470Level: Starter
471
472Remove disable/unprepare in remove/shutdown in panel-simple and panel-edp
473-------------------------------------------------------------------------
474
475As of commit d2aacaf07395 ("drm/panel: Check for already prepared/enabled in
476drm_panel"), we have a check in the drm_panel core to make sure nobody
477double-calls prepare/enable/disable/unprepare. Eventually that should probably
478be turned into a WARN_ON() or somehow made louder.
479
480At the moment, we expect that we may still encounter the warnings in the
481drm_panel core when using panel-simple and panel-edp. Since those panel
482drivers are used with a lot of different DRM modeset drivers they still
483make an extra effort to disable/unprepare the panel themsevles at shutdown
484time. Specifically we could still encounter those warnings if the panel
485driver gets shutdown() _before_ the DRM modeset driver and the DRM modeset
486driver properly calls drm_atomic_helper_shutdown() in its own shutdown()
487callback. Warnings could be avoided in such a case by using something like
488device links to ensure that the panel gets shutdown() after the DRM modeset
489driver.
490
491Once all DRM modeset drivers are known to shutdown properly, the extra
492calls to disable/unprepare in remove/shutdown in panel-simple and panel-edp
493should be removed and this TODO item marked complete.
494
495Contact: Douglas Anderson <dianders@chromium.org>
496
497Level: Intermediate
498
499Transition away from using mipi_dsi_*_write_seq()
500-------------------------------------------------
501
502The macros mipi_dsi_generic_write_seq() and mipi_dsi_dcs_write_seq() are
503non-intuitive because, if there are errors, they return out of the *caller's*
504function. We should move all callers to use mipi_dsi_generic_write_seq_multi()
505and mipi_dsi_dcs_write_seq_multi() macros instead.
506
507Once all callers are transitioned, the macros and the functions that they call,
508mipi_dsi_generic_write_chatty() and mipi_dsi_dcs_write_buffer_chatty(), can
509probably be removed. Alternatively, if people feel like the _multi() variants
510are overkill for some use cases, we could keep the mipi_dsi_*_write_seq()
511variants but change them not to return out of the caller.
512
513Contact: Douglas Anderson <dianders@chromium.org>
514
515Level: Starter
516
517
518Core refactorings
519=================
520
521Make panic handling work
522------------------------
523
524This is a really varied tasks with lots of little bits and pieces:
525
526* The panic path can't be tested currently, leading to constant breaking. The
527  main issue here is that panics can be triggered from hardirq contexts and
528  hence all panic related callback can run in hardirq context. It would be
529  awesome if we could test at least the fbdev helper code and driver code by
530  e.g. trigger calls through drm debugfs files. hardirq context could be
531  achieved by using an IPI to the local processor.
532
533* There's a massive confusion of different panic handlers. DRM fbdev emulation
534  helpers had their own (long removed), but on top of that the fbcon code itself
535  also has one. We need to make sure that they stop fighting over each other.
536  This is worked around by checking ``oops_in_progress`` at various entry points
537  into the DRM fbdev emulation helpers. A much cleaner approach here would be to
538  switch fbcon to the `threaded printk support
539  <https://lwn.net/Articles/800946/>`_.
540
541* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
542  isn't a full solution for panic paths. We need to make sure that it only
543  returns true if there's a panic going on for real, and fix up all the
544  fallout.
545
546* The panic handler must never sleep, which also means it can't ever
547  ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
548  even spinlocks (because NMI and hardirq can panic too). We need to either
549  make sure to not call such paths, or trylock everything. Really tricky.
550
551* A clean solution would be an entirely separate panic output support in KMS,
552  bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling
553  <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_.
554
555* Encoding the actual oops and preceding dmesg in a QR might help with the
556  dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages
557  transfer using QR codes
558  <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_
559  for some example code that could be reused.
 
560
561Contact: Simona Vetter
562
563Level: Advanced
564
565Clean up the debugfs support
566----------------------------
567
568There's a bunch of issues with it:
569
570- Convert drivers to support the drm_debugfs_add_files() function instead of
571  the drm_debugfs_create_files() function.
572
573- Improve late-register debugfs by rolling out the same debugfs pre-register
574  infrastructure for connector and crtc too. That way, the drivers won't need to
575  split their setup code into init and register anymore.
576
577- We probably want to have some support for debugfs files on crtc/connectors and
578  maybe other kms objects directly in core. There's even drm_print support in
579  the funcs for these objects to dump kms state, so it's all there. And then the
580  ->show() functions should obviously give you a pointer to the right object.
581
 
 
 
582- The drm_driver->debugfs_init hooks we have is just an artifact of the old
583  midlayered load sequence. DRM debugfs should work more like sysfs, where you
584  can create properties/files for an object anytime you want, and the core
585  takes care of publishing/unpuplishing all the files at register/unregister
586  time. Drivers shouldn't need to worry about these technicalities, and fixing
587  this (together with the drm_minor->drm_device move) would allow us to remove
588  debugfs_init.
589
590Contact: Simona Vetter
591
592Level: Intermediate
593
594Object lifetime fixes
595---------------------
596
597There's two related issues here
598
599- Cleanup up the various ->destroy callbacks, which often are all the same
600  simple code.
601
602- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc,
603  which results in use-after free issues on driver unload. This can be serious
604  trouble even for drivers for hardware integrated on the SoC due to
605  EPROBE_DEFERRED backoff.
606
607Both these problems can be solved by switching over to drmm_kzalloc(), and the
608various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(),
609drmm_universal_plane_alloc(), ... and so on.
610
611Contact: Simona Vetter
612
613Level: Intermediate
614
615Remove automatic page mapping from dma-buf importing
616----------------------------------------------------
617
618When importing dma-bufs, the dma-buf and PRIME frameworks automatically map
619imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and
620drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach()
621even if they never do actual device DMA, but only CPU access through
622dma_buf_vmap(). This is a problem for USB devices, which do not support DMA
623operations.
624
625To fix the issue, automatic page mappings should be removed from the
626buffer-sharing code. Fixing this is a bit more involved, since the import/export
627cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over
628this problem for USB devices by fishing out the USB host controller device, as
629long as that supports DMA. Otherwise importing can still needlessly fail.
630
631Contact: Thomas Zimmermann <tzimmermann@suse.de>, Simona Vetter
 
 
 
632
633Level: Advanced
 
 
 
634
 
635
636Better Testing
637==============
638
639Add unit tests using the Kernel Unit Testing (KUnit) framework
640--------------------------------------------------------------
641
642The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_
643provides a common framework for unit tests within the Linux kernel. Having a
644test suite would allow to identify regressions earlier.
645
646A good candidate for the first unit tests are the format-conversion helpers in
647``drm_format_helper.c``.
648
649Contact: Javier Martinez Canillas <javierm@redhat.com>
650
651Level: Intermediate
652
653Clean up and document former selftests suites
654---------------------------------------------
655
656Some KUnit test suites (drm_buddy, drm_cmdline_parser, drm_damage_helper,
657drm_format, drm_framebuffer, drm_dp_mst_helper, drm_mm, drm_plane_helper and
658drm_rect) are former selftests suites that have been converted over when KUnit
659was first introduced.
660
661These suites were fairly undocumented, and with different goals than what unit
662tests can be. Trying to identify what each test in these suites actually test
663for, whether that makes sense for a unit test, and either remove it if it
664doesn't or document it if it does would be of great help.
665
666Contact: Maxime Ripard <mripard@kernel.org>
667
668Level: Intermediate
669
670Enable trinity for DRM
671----------------------
672
673And fix up the fallout. Should be really interesting ...
674
675Level: Advanced
676
677Make KMS tests in i-g-t generic
678-------------------------------
679
680The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
681including tons of testcases for corner-cases in the modesetting API. It would
682be awesome if those tests (at least the ones not relying on Intel-specific GEM
683features) could be made to run on any KMS driver.
684
685Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
686converting things over. For modeset tests we also first need a bit of
687infrastructure to use dumb buffers for untiled buffers, to be able to run all
688the non-i915 specific modeset tests.
689
690Level: Advanced
691
692Extend virtual test driver (VKMS)
693---------------------------------
694
695See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
696internship task, since it only requires a virtual machine and can be sized to
697fit the available time.
698
 
 
699Level: See details
700
701Backlight Refactoring
702---------------------
703
704Backlight drivers have a triple enable/disable state, which is a bit overkill.
705Plan to fix this:
706
7071. Roll out backlight_enable() and backlight_disable() helpers everywhere. This
708   has started already.
7092. In all, only look at one of the three status bits set by the above helpers.
7103. Remove the other two status bits.
711
712Contact: Simona Vetter
713
714Level: Intermediate
715
716Driver Specific
717===============
718
719AMD DC Display Driver
720---------------------
721
722AMD DC is the display driver for AMD devices starting with Vega. There has been
723a bunch of progress cleaning it up but there's still plenty of work to be done.
724
725See drivers/gpu/drm/amd/display/TODO for tasks.
726
727Contact: Harry Wentland, Alex Deucher
728
729Bootsplash
730==========
731
732There is support in place now for writing internal DRM clients making it
733possible to pick up the bootsplash work that was rejected because it was written
734for fbdev.
735
736- [v6,8/8] drm/client: Hack: Add bootsplash example
737  https://patchwork.freedesktop.org/patch/306579/
738
739- [RFC PATCH v2 00/13] Kernel based bootsplash
740  https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de
741
742Contact: Sam Ravnborg
743
744Level: Advanced
745
746Brightness handling on devices with multiple internal panels
747============================================================
748
749On x86/ACPI devices there can be multiple backlight firmware interfaces:
750(ACPI) video, vendor specific and others. As well as direct/native (PWM)
751register programming by the KMS driver.
752
753To deal with this backlight drivers used on x86/ACPI call
754acpi_video_get_backlight_type() which has heuristics (+quirks) to select
755which backlight interface to use; and backlight drivers which do not match
756the returned type will not register themselves, so that only one backlight
757device gets registered (in a single GPU setup, see below).
758
759At the moment this more or less assumes that there will only
760be 1 (internal) panel on a system.
761
762On systems with 2 panels this may be a problem, depending on
763what interface acpi_video_get_backlight_type() selects:
764
7651. native: in this case the KMS driver is expected to know which backlight
766   device belongs to which output so everything should just work.
7672. video: this does support controlling multiple backlights, but some work
768   will need to be done to get the output <-> backlight device mapping
769
770The above assumes both panels will require the same backlight interface type.
771Things will break on systems with multiple panels where the 2 panels need
772a different type of control. E.g. one panel needs ACPI video backlight control,
773where as the other is using native backlight control. Currently in this case
774only one of the 2 required backlight devices will get registered, based on
775the acpi_video_get_backlight_type() return value.
776
777If this (theoretical) case ever shows up, then supporting this will need some
778work. A possible solution here would be to pass a device and connector-name
779to acpi_video_get_backlight_type() so that it can deal with this.
780
781Note in a way we already have a case where userspace sees 2 panels,
782in dual GPU laptop setups with a mux. On those systems we may see
783either 2 native backlight devices; or 2 native backlight devices.
784
785Userspace already has code to deal with this by detecting if the related
786panel is active (iow which way the mux between the GPU and the panels
787points) and then uses that backlight device. Userspace here very much
788assumes a single panel though. It picks only 1 of the 2 backlight devices
789and then only uses that one.
790
791Note that all userspace code (that I know off) is currently hardcoded
792to assume a single panel.
793
794Before the recent changes to not register multiple (e.g. video + native)
795/sys/class/backlight devices for a single panel (on a single GPU laptop),
796userspace would see multiple backlight devices all controlling the same
797backlight.
798
799To deal with this userspace had to always picks one preferred device under
800/sys/class/backlight and will ignore the others. So to support brightness
801control on multiple panels userspace will need to be updated too.
802
803There are plans to allow brightness control through the KMS API by adding
804a "display brightness" property to drm_connector objects for panels. This
805solves a number of issues with the /sys/class/backlight API, including not
806being able to map a sysfs backlight device to a specific connector. Any
807userspace changes to add support for brightness control on devices with
808multiple panels really should build on top of this new KMS property.
809
810Contact: Hans de Goede
811
812Level: Advanced
813
814Buffer age or other damage accumulation algorithm for buffer damage
815===================================================================
816
817Drivers that do per-buffer uploads, need a buffer damage handling (rather than
818frame damage like drivers that do per-plane or per-CRTC uploads), but there is
819no support to get the buffer age or any other damage accumulation algorithm.
820
821For this reason, the damage helpers just fallback to a full plane update if the
822framebuffer attached to a plane has changed since the last page-flip. Drivers
823set &drm_plane_state.ignore_damage_clips to true as indication to
824drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next()
825helpers that the damage clips should be ignored.
826
827This should be improved to get damage tracking properly working on drivers that
828do per-buffer uploads.
829
830More information about damage tracking and references to learning materials can
831be found in :ref:`damage_tracking_properties`.
832
833Contact: Javier Martinez Canillas <javierm@redhat.com>
834
835Level: Advanced
836
837Querying errors from drm_syncobj
838================================
839
840The drm_syncobj container can be used by driver independent code to signal
841complection of submission.
842
843One minor feature still missing is a generic DRM IOCTL to query the error
844status of binary and timeline drm_syncobj.
845
846This should probably be improved by implementing the necessary kernel interface
847and adding support for that in the userspace stack.
848
849Contact: Christian König
850
851Level: Starter
852
853Outside DRM
854===========
855
856Convert fbdev drivers to DRM
857----------------------------
858
859There are plenty of fbdev drivers for older hardware. Some hardware has
860become obsolete, but some still provides good(-enough) framebuffers. The
861drivers that are still useful should be converted to DRM and afterwards
862removed from fbdev.
863
864Very simple fbdev drivers can best be converted by starting with a new
865DRM driver. Simple KMS helpers and SHMEM should be able to handle any
866existing hardware. The new driver's call-back functions are filled from
867existing fbdev code.
868
869More complex fbdev drivers can be refactored step-by-step into a DRM
870driver with the help of the DRM fbconv helpers [4]_. These helpers provide
871the transition layer between the DRM core infrastructure and the fbdev
872driver interface. Create a new DRM driver on top of the fbconv helpers,
873copy over the fbdev driver, and hook it up to the DRM code. Examples for
874several fbdev drivers are available in Thomas Zimmermann's fbconv tree
875[4]_, as well as a tutorial of this process [5]_. The result is a primitive
876DRM driver that can run X11 and Weston.
877
878 .. [4] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv
879 .. [5] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c
880
881Contact: Thomas Zimmermann <tzimmermann@suse.de>
882
883Level: Advanced

  1.. _todo:
  2
  3=========
  4TODO list
  5=========
  6
  7This section contains a list of smaller janitorial tasks in the kernel DRM
  8graphics subsystem useful as newbie projects. Or for slow rainy days.
  9
 10Difficulty
 11----------
 12
 13To make it easier task are categorized into different levels:
 14
 15Starter: Good tasks to get started with the DRM subsystem.
 16
 17Intermediate: Tasks which need some experience with working in the DRM
 18subsystem, or some specific GPU/display graphics knowledge. For debugging issue
 19it's good to have the relevant hardware (or a virtual driver set up) available
 20for testing.
 21
 22Advanced: Tricky tasks that need fairly good understanding of the DRM subsystem
 23and graphics topics. Generally need the relevant hardware for development and
 24testing.
 25
 
 
 
 26Subsystem-wide refactorings
 27===========================
 28
 29Remove custom dumb_map_offset implementations
 30---------------------------------------------
 31
 32All GEM based drivers should be using drm_gem_create_mmap_offset() instead.
 33Audit each individual driver, make sure it'll work with the generic
 34implementation (there's lots of outdated locking leftovers in various
 35implementations), and then remove it.
 36
 37Contact: Daniel Vetter, respective driver maintainers
 38
 39Level: Intermediate
 40
 41Convert existing KMS drivers to atomic modesetting
 42--------------------------------------------------
 43
 443.19 has the atomic modeset interfaces and helpers, so drivers can now be
 45converted over. Modern compositors like Wayland or Surfaceflinger on Android
 46really want an atomic modeset interface, so this is all about the bright
 47future.
 48
 49There is a conversion guide for atomic and all you need is a GPU for a
 50non-converted driver (again virtual HW drivers for KVM are still all
 51suitable).
 52
 53As part of this drivers also need to convert to universal plane (which means
 54exposing primary & cursor as proper plane objects). But that's much easier to
 55do by directly using the new atomic helper driver callbacks.
 56
 57Contact: Daniel Vetter, respective driver maintainers
 
 
 
 
 58
 59Level: Advanced
 60
 61Clean up the clipped coordination confusion around planes
 62---------------------------------------------------------
 63
 64We have a helper to get this right with drm_plane_helper_check_update(), but
 65it's not consistently used. This should be fixed, preferrably in the atomic
 66helpers (and drivers then moved over to clipped coordinates). Probably the
 67helper should also be moved from drm_plane_helper.c to the atomic helpers, to
 68avoid confusion - the other helpers in that file are all deprecated legacy
 69helpers.
 70
 71Contact: Ville Syrjälä, Daniel Vetter, driver maintainers
 72
 73Level: Advanced
 74
 75Improve plane atomic_check helpers
 76----------------------------------
 77
 78Aside from the clipped coordinates right above there's a few suboptimal things
 79with the current helpers:
 80
 81- drm_plane_helper_funcs->atomic_check gets called for enabled or disabled
 82  planes. At best this seems to confuse drivers, worst it means they blow up
 83  when the plane is disabled without the CRTC. The only special handling is
 84  resetting values in the plane state structures, which instead should be moved
 85  into the drm_plane_funcs->atomic_duplicate_state functions.
 86
 87- Once that's done, helpers could stop calling ->atomic_check for disabled
 88  planes.
 89
 90- Then we could go through all the drivers and remove the more-or-less confused
 91  checks for plane_state->fb and plane_state->crtc.
 92
 93Contact: Daniel Vetter
 94
 95Level: Advanced
 96
 97Convert early atomic drivers to async commit helpers
 98----------------------------------------------------
 99
100For the first year the atomic modeset helpers didn't support asynchronous /
101nonblocking commits, and every driver had to hand-roll them. This is fixed
102now, but there's still a pile of existing drivers that easily could be
103converted over to the new infrastructure.
104
105One issue with the helpers is that they require that drivers handle completion
106events for atomic commits correctly. But fixing these bugs is good anyway.
107
108Contact: Daniel Vetter, respective driver maintainers
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
109
110Level: Advanced
111
112Fallout from atomic KMS
113-----------------------
114
115``drm_atomic_helper.c`` provides a batch of functions which implement legacy
116IOCTLs on top of the new atomic driver interface. Which is really nice for
117gradual conversion of drivers, but unfortunately the semantic mismatches are
118a bit too severe. So there's some follow-up work to adjust the function
119interfaces to fix these issues:
120
121* atomic needs the lock acquire context. At the moment that's passed around
122  implicitly with some horrible hacks, and it's also allocate with
123  ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
124  the acquire context explicitly on stack and then also pass it down into
125  drivers explicitly so that the legacy-on-atomic functions can use them.
126
127  Except for some driver code this is done. This task should be finished by
128  adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
129
130* A bunch of the vtable hooks are now in the wrong place: DRM has a split
131  between core vfunc tables (named ``drm_foo_funcs``), which are used to
132  implement the userspace ABI. And then there's the optional hooks for the
133  helper libraries (name ``drm_foo_helper_funcs``), which are purely for
134  internal use. Some of these hooks should be move from ``_funcs`` to
135  ``_helper_funcs`` since they are not part of the core ABI. There's a
136  ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
137
138Contact: Daniel Vetter
139
140Level: Intermediate
141
142Get rid of dev->struct_mutex from GEM drivers
143---------------------------------------------
144
145``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
146everything. Nowadays in modern drivers the only bit where it's mandatory is
147serializing GEM buffer object destruction. Which unfortunately means drivers
148have to keep track of that lock and either call ``unreference`` or
149``unreference_locked`` depending upon context.
150
151Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
152and there's a ``gem_free_object_unlocked`` callback for any drivers which are
153entirely ``struct_mutex`` free.
154
155For drivers that need ``struct_mutex`` it should be replaced with a driver-
156private lock. The tricky part is the BO free functions, since those can't
157reliably take that lock any more. Instead state needs to be protected with
158suitable subordinate locks or some cleanup work pushed to a worker thread. For
159performance-critical drivers it might also be better to go with a more
160fine-grained per-buffer object and per-context lockings scheme. Currently only
161the ``msm`` and `i915` drivers use ``struct_mutex``.
162
163Contact: Daniel Vetter, respective driver maintainers
164
165Level: Advanced
166
167Convert logging to drm_* functions with drm_device paramater
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
168------------------------------------------------------------
169
170For drivers which could have multiple instances, it is necessary to
171differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
172don't do this, drivers used dev_info/warn/err to make this differentiation. We
173now have drm_* variants of the drm print functions, so we can start to convert
174those drivers back to using drm-formatted specific log messages.
175
176Before you start this conversion please contact the relevant maintainers to make
177sure your work will be merged - not everyone agrees that the DRM dmesg macros
178are better.
179
180Contact: Sean Paul, Maintainer of the driver you plan to convert
181
182Level: Starter
183
184Convert drivers to use simple modeset suspend/resume
185----------------------------------------------------
186
187Most drivers (except i915 and nouveau) that use
188drm_atomic_helper_suspend/resume() can probably be converted to use
189drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
190of the atomic suspend/resume code in older atomic modeset drivers.
191
192Contact: Maintainer of the driver you plan to convert
193
194Level: Intermediate
195
196Convert drivers to use drm_fbdev_generic_setup()
197------------------------------------------------
 
 
 
 
 
 
 
 
 
198
199Most drivers can use drm_fbdev_generic_setup(). Driver have to implement
200atomic modesetting and GEM vmap support. Current generic fbdev emulation
201expects the framebuffer in system memory (or system-like memory).
202
203Contact: Maintainer of the driver you plan to convert
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
204
205Level: Intermediate
206
207drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup
208-----------------------------------------------------------------
209
210A lot more drivers could be switched over to the drm_gem_framebuffer helpers.
211Various hold-ups:
212
213- Need to switch over to the generic dirty tracking code using
214  drm_atomic_helper_dirtyfb first (e.g. qxl).
215
216- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb
217  setup code can't be deleted.
218
219- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For
220  atomic drivers we could check for valid formats by calling
221  drm_plane_check_pixel_format() against all planes, and pass if any plane
222  supports the format. For non-atomic that's not possible since like the format
223  list for the primary plane is fake and we'd therefor reject valid formats.
224
225- Many drivers subclass drm_framebuffer, we'd need a embedding compatible
226  version of the varios drm_gem_fb_create functions. Maybe called
227  drm_gem_fb_create/_with_dirty/_with_funcs as needed.
228
229Contact: Daniel Vetter
230
231Level: Intermediate
232
233Clean up mmap forwarding
234------------------------
235
236A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
237And also a lot of them forward dma-buf mmap to the gem mmap implementations.
238There's drm_gem_prime_mmap() for this now, but still needs to be rolled out.
239
240Contact: Daniel Vetter
241
242Level: Intermediate
243
244Generic fbdev defio support
245---------------------------
246
247The defio support code in the fbdev core has some very specific requirements,
248which means drivers need to have a special framebuffer for fbdev. The main
249issue is that it uses some fields in struct page itself, which breaks shmem
250gem objects (and other things). To support defio, affected drivers require
251the use of a shadow buffer, which may add CPU and memory overhead.
252
253Possible solution would be to write our own defio mmap code in the drm fbdev
254emulation. It would need to fully wrap the existing mmap ops, forwarding
255everything after it has done the write-protect/mkwrite trickery:
256
257- In the drm_fbdev_fb_mmap helper, if we need defio, change the
258  default page prots to write-protected with something like this::
259
260      vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot);
261
262- Set the mkwrite and fsync callbacks with similar implementions to the core
263  fbdev defio stuff. These should all work on plain ptes, they don't actually
264  require a struct page.  uff. These should all work on plain ptes, they don't
265  actually require a struct page.
266
267- Track the dirty pages in a separate structure (bitfield with one bit per page
268  should work) to avoid clobbering struct page.
269
270Might be good to also have some igt testcases for this.
271
272Contact: Daniel Vetter, Noralf Tronnes
273
274Level: Advanced
275
276idr_init_base()
277---------------
278
279DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
280userspace IDs to internal objects, and in most places ID=0 means NULL and hence
281is never used. Switching to idr_init_base() for these would make the idr more
282efficient.
283
284Contact: Daniel Vetter
285
286Level: Starter
287
288struct drm_gem_object_funcs
289---------------------------
290
291GEM objects can now have a function table instead of having the callbacks on the
292DRM driver struct. This is now the preferred way and drivers can be moved over.
293
294We also need a 2nd version of the CMA define that doesn't require the
295vmapping to be present (different hook for prime importing). Plus this needs to
296be rolled out to all drivers using their own implementations, too.
297
298Level: Intermediate
299
300Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate
301---------------------------------------------------------
302
303For cases where drivers are attempting to grab the modeset locks with a local
304acquire context. Replace the boilerplate code surrounding
305drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and
306DRM_MODESET_LOCK_ALL_END() instead.
307
308This should also be done for all places where drm_modeset_lock_all() is still
309used.
310
311As a reference, take a look at the conversions already completed in drm core.
312
313Contact: Sean Paul, respective driver maintainers
314
315Level: Starter
316
317Rename CMA helpers to DMA helpers
318---------------------------------
319
320CMA (standing for contiguous memory allocator) is really a bit an accident of
321what these were used for first, a much better name would be DMA helpers. In the
322text these should even be called coherent DMA memory helpers (so maybe CDM, but
323no one knows what that means) since underneath they just use dma_alloc_coherent.
324
325Contact: Laurent Pinchart, Daniel Vetter
326
327Level: Intermediate (mostly because it is a huge tasks without good partial
328milestones, not technically itself that challenging)
329
330connector register/unregister fixes
331-----------------------------------
332
333- For most connectors it's a no-op to call drm_connector_register/unregister
334  directly from driver code, drm_dev_register/unregister take care of this
335  already. We can remove all of them.
336
337- For dp drivers it's a bit more a mess, since we need the connector to be
338  registered when calling drm_dp_aux_register. Fix this by instead calling
339  drm_dp_aux_init, and moving the actual registering into a late_register
340  callback as recommended in the kerneldoc.
341
342Level: Intermediate
343
344Remove load/unload callbacks from all non-DRIVER_LEGACY drivers
345---------------------------------------------------------------
346
347The load/unload callbacks in struct &drm_driver are very much midlayers, plus
348for historical reasons they get the ordering wrong (and we can't fix that)
349between setting up the &drm_driver structure and calling drm_dev_register().
350
351- Rework drivers to no longer use the load/unload callbacks, directly coding the
352  load/unload sequence into the driver's probe function.
353
354- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload
355  callbacks for all modern drivers.
356
357Contact: Daniel Vetter
358
359Level: Intermediate
360
361Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi
362---------------------------------------------------------------
363
364Once EDID is parsed, the monitor HDMI support information is available through
365drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to
366retrieve the same information, which is less efficient.
367
368Audit each individual driver calling drm_detect_hdmi_monitor() and switch to
369drm_display_info.is_hdmi if applicable.
370
371Contact: Laurent Pinchart, respective driver maintainers
372
373Level: Intermediate
374
375Consolidate custom driver modeset properties
376--------------------------------------------
377
378Before atomic modeset took place, many drivers where creating their own
379properties. Among other things, atomic brought the requirement that custom,
380driver specific properties should not be used.
381
382For this task, we aim to introduce core helpers or reuse the existing ones
383if available:
384
385A quick, unconfirmed, examples list.
386
387Introduce core helpers:
388- audio (amdgpu, intel, gma500, radeon)
389- brightness, contrast, etc (armada, nouveau) - overlay only (?)
390- broadcast rgb (gma500, intel)
391- colorkey (armada, nouveau, rcar) - overlay only (?)
392- dither (amdgpu, nouveau, radeon) - varies across drivers
393- underscan family (amdgpu, radeon, nouveau)
394
395Already in core:
396- colorspace (sti)
397- tv format names, enhancements (gma500, intel)
398- tv overscan, margins, etc. (gma500, intel)
399- zorder (omapdrm) - same as zpos (?)
400
401
402Contact: Emil Velikov, respective driver maintainers
403
404Level: Intermediate
405
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
406
407Core refactorings
408=================
409
410Make panic handling work
411------------------------
412
413This is a really varied tasks with lots of little bits and pieces:
414
415* The panic path can't be tested currently, leading to constant breaking. The
416  main issue here is that panics can be triggered from hardirq contexts and
417  hence all panic related callback can run in hardirq context. It would be
418  awesome if we could test at least the fbdev helper code and driver code by
419  e.g. trigger calls through drm debugfs files. hardirq context could be
420  achieved by using an IPI to the local processor.
421
422* There's a massive confusion of different panic handlers. DRM fbdev emulation
423  helpers have one, but on top of that the fbcon code itself also has one. We
424  need to make sure that they stop fighting over each another.
 
 
 
 
425
426* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
427  isn't a full solution for panic paths. We need to make sure that it only
428  returns true if there's a panic going on for real, and fix up all the
429  fallout.
430
431* The panic handler must never sleep, which also means it can't ever
432  ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
433  even spinlocks (because NMI and hardirq can panic too). We need to either
434  make sure to not call such paths, or trylock everything. Really tricky.
435
436* For the above locking troubles reasons it's pretty much impossible to
437  attempt a synchronous modeset from panic handlers. The only thing we could
438  try to achive is an atomic ``set_base`` of the primary plane, and hope that
439  it shows up. Everything else probably needs to be delayed to some worker or
440  something else which happens later on. Otherwise it just kills the box
441  harder, prevent the panic from going out on e.g. netconsole.
442
443* There's also proposal for a simplied DRM console instead of the full-blown
444  fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
445  obviously work for both console, in case we ever get kmslog merged.
446
447Contact: Daniel Vetter
448
449Level: Advanced
450
451Clean up the debugfs support
452----------------------------
453
454There's a bunch of issues with it:
455
456- The drm_info_list ->show() function doesn't even bother to cast to the drm
457  structure for you. This is lazy.
 
 
 
 
458
459- We probably want to have some support for debugfs files on crtc/connectors and
460  maybe other kms objects directly in core. There's even drm_print support in
461  the funcs for these objects to dump kms state, so it's all there. And then the
462  ->show() functions should obviously give you a pointer to the right object.
463
464- The drm_info_list stuff is centered on drm_minor instead of drm_device. For
465  anything we want to print drm_device (or maybe drm_file) is the right thing.
466
467- The drm_driver->debugfs_init hooks we have is just an artifact of the old
468  midlayered load sequence. DRM debugfs should work more like sysfs, where you
469  can create properties/files for an object anytime you want, and the core
470  takes care of publishing/unpuplishing all the files at register/unregister
471  time. Drivers shouldn't need to worry about these technicalities, and fixing
472  this (together with the drm_minor->drm_device move) would allow us to remove
473  debugfs_init.
474
475- Drop the return code and error checking from all debugfs functions. Greg KH is
476  working on this already.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
477
478Contact: Daniel Vetter
 
 
 
 
479
480Level: Intermediate
481
482KMS cleanups
483------------
484
485Some of these date from the very introduction of KMS in 2008 ...
 
 
 
 
 
 
 
 
 
 
 
486
487- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
488  function tables in drivers, but before we can remove them we need to make sure
489  that all the users in helpers and drivers do correctly check for a NULL
490  vtable.
491
492- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
493  drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
494  end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
495  historical reasons) misnamed drm_primary_helper_destroy() function.
496
497Level: Intermediate
498
499Better Testing
500==============
501
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
502Enable trinity for DRM
503----------------------
504
505And fix up the fallout. Should be really interesting ...
506
507Level: Advanced
508
509Make KMS tests in i-g-t generic
510-------------------------------
511
512The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
513including tons of testcases for corner-cases in the modesetting API. It would
514be awesome if those tests (at least the ones not relying on Intel-specific GEM
515features) could be made to run on any KMS driver.
516
517Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
518converting things over. For modeset tests we also first need a bit of
519infrastructure to use dumb buffers for untiled buffers, to be able to run all
520the non-i915 specific modeset tests.
521
522Level: Advanced
523
524Extend virtual test driver (VKMS)
525---------------------------------
526
527See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
528internship task, since it only requires a virtual machine and can be sized to
529fit the available time.
530
531Contact: Daniel Vetter
532
533Level: See details
534
535Backlight Refactoring
536---------------------
537
538Backlight drivers have a triple enable/disable state, which is a bit overkill.
539Plan to fix this:
540
5411. Roll out backlight_enable() and backlight_disable() helpers everywhere. This
542   has started already.
5432. In all, only look at one of the three status bits set by the above helpers.
5443. Remove the other two status bits.
545
546Contact: Daniel Vetter
547
548Level: Intermediate
549
550Driver Specific
551===============
552
553AMD DC Display Driver
554---------------------
555
556AMD DC is the display driver for AMD devices starting with Vega. There has been
557a bunch of progress cleaning it up but there's still plenty of work to be done.
558
559See drivers/gpu/drm/amd/display/TODO for tasks.
560
561Contact: Harry Wentland, Alex Deucher
562
563Bootsplash
564==========
565
566There is support in place now for writing internal DRM clients making it
567possible to pick up the bootsplash work that was rejected because it was written
568for fbdev.
569
570- [v6,8/8] drm/client: Hack: Add bootsplash example
571  https://patchwork.freedesktop.org/patch/306579/
572
573- [RFC PATCH v2 00/13] Kernel based bootsplash
574  https://lkml.org/lkml/2017/12/13/764
575
576Contact: Sam Ravnborg
577
578Level: Advanced
579
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
580Outside DRM
581===========
582
583Convert fbdev drivers to DRM
584----------------------------
585
586There are plenty of fbdev drivers for older hardware. Some hwardware has
587become obsolete, but some still provides good(-enough) framebuffers. The
588drivers that are still useful should be converted to DRM and afterwards
589removed from fbdev.
590
591Very simple fbdev drivers can best be converted by starting with a new
592DRM driver. Simple KMS helpers and SHMEM should be able to handle any
593existing hardware. The new driver's call-back functions are filled from
594existing fbdev code.
595
596More complex fbdev drivers can be refactored step-by-step into a DRM
597driver with the help of the DRM fbconv helpers. [1] These helpers provide
598the transition layer between the DRM core infrastructure and the fbdev
599driver interface. Create a new DRM driver on top of the fbconv helpers,
600copy over the fbdev driver, and hook it up to the DRM code. Examples for
601several fbdev drivers are available at [1] and a tutorial of this process
602available at [2]. The result is a primitive DRM driver that can run X11
603and Weston.
604
605 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv
606 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c
607
608Contact: Thomas Zimmermann <tzimmermann@suse.de>
609
610Level: Advanced