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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37implementation (there's lots of outdated locking leftovers in various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
10Subsystem-wide refactorings
11===========================
12
13De-midlayer drivers
14-------------------
15
16With the recent ``drm_bus`` cleanup patches for 3.17 it is no longer required
17to have a ``drm_bus`` structure set up. Drivers can directly set up the
18``drm_device`` structure instead of relying on bus methods in ``drm_usb.c``
19and ``drm_pci.c``. The goal is to get rid of the driver's ``->load`` /
20``->unload`` callbacks and open-code the load/unload sequence properly, using
21the new two-stage ``drm_device`` setup/teardown.
22
23Once all existing drivers are converted we can also remove those bus support
24files for USB and platform devices.
25
26All you need is a GPU for a non-converted driver (currently almost all of
27them, but also all the virtual ones used by KVM, so everyone qualifies).
28
29Contact: Daniel Vetter, Thierry Reding, respective driver maintainers
30
31Switch from reference/unreference to get/put
32--------------------------------------------
33
34For some reason DRM core uses ``reference``/``unreference`` suffixes for
35refcounting functions, but kernel uses ``get``/``put`` (e.g.
36``kref_get``/``put()``). It would be good to switch over for consistency, and
37it's shorter. Needs to be done in 3 steps for each pair of functions:
38
39* Create new ``get``/``put`` functions, define the old names as compatibility
40 wrappers
41* Switch over each file/driver using a cocci-generated spatch.
42* Once all users of the old names are gone, remove them.
43
44This way drivers/patches in the progress of getting merged won't break.
45
46Contact: Daniel Vetter
47
48Convert existing KMS drivers to atomic modesetting
49--------------------------------------------------
50
513.19 has the atomic modeset interfaces and helpers, so drivers can now be
52converted over. Modern compositors like Wayland or Surfaceflinger on Android
53really want an atomic modeset interface, so this is all about the bright
54future.
55
56There is a conversion guide for atomic and all you need is a GPU for a
57non-converted driver (again virtual HW drivers for KVM are still all
58suitable).
59
60As part of this drivers also need to convert to universal plane (which means
61exposing primary & cursor as proper plane objects). But that's much easier to
62do by directly using the new atomic helper driver callbacks.
63
64Contact: Daniel Vetter, respective driver maintainers
65
66Clean up the clipped coordination confusion around planes
67---------------------------------------------------------
68
69We have a helper to get this right with drm_plane_helper_check_update(), but
70it's not consistently used. This should be fixed, preferrably in the atomic
71helpers (and drivers then moved over to clipped coordinates). Probably the
72helper should also be moved from drm_plane_helper.c to the atomic helpers, to
73avoid confusion - the other helpers in that file are all deprecated legacy
74helpers.
75
76Contact: Ville Syrjälä, Daniel Vetter, driver maintainers
77
78Convert early atomic drivers to async commit helpers
79----------------------------------------------------
80
81For the first year the atomic modeset helpers didn't support asynchronous /
82nonblocking commits, and every driver had to hand-roll them. This is fixed
83now, but there's still a pile of existing drivers that easily could be
84converted over to the new infrastructure.
85
86One issue with the helpers is that they require that drivers handle completion
87events for atomic commits correctly. But fixing these bugs is good anyway.
88
89Contact: Daniel Vetter, respective driver maintainers
90
91Better manual-upload support for atomic
92---------------------------------------
93
94This would be especially useful for tinydrm:
95
96- Add a struct drm_rect dirty_clip to drm_crtc_state. When duplicating the
97 crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in
98 __drm_atomic_helper_crtc_duplicate_state().
99
100- Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_
101 prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this
102 is a function useful to implement the fb->dirty function.
103
104- Create a new drm_fb_dirty function which does essentially what e.g.
105 mipi_dbi_fb_dirty does. You can use e.g. drm_atomic_helper_update_plane as the
106 template. But instead of doing a simple full-screen plane update, this new
107 helper also sets crtc_state->dirty_clip to the right coordinates. And of
108 course it needs to check whether the fb is actually active (and maybe where),
109 so there's some book-keeping involved. There's also some good fun involved in
110 scaling things appropriately. For that case we might simply give up and
111 declare the entire area covered by the plane as dirty.
112
113Contact: Noralf Trønnes, Daniel Vetter
114
115Fallout from atomic KMS
116-----------------------
117
118``drm_atomic_helper.c`` provides a batch of functions which implement legacy
119IOCTLs on top of the new atomic driver interface. Which is really nice for
120gradual conversion of drivers, but unfortunately the semantic mismatches are
121a bit too severe. So there's some follow-up work to adjust the function
122interfaces to fix these issues:
123
124* atomic needs the lock acquire context. At the moment that's passed around
125 implicitly with some horrible hacks, and it's also allocate with
126 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
127 the acquire context explicitly on stack and then also pass it down into
128 drivers explicitly so that the legacy-on-atomic functions can use them.
129
130 Except for some driver code this is done.
131
132* A bunch of the vtable hooks are now in the wrong place: DRM has a split
133 between core vfunc tables (named ``drm_foo_funcs``), which are used to
134 implement the userspace ABI. And then there's the optional hooks for the
135 helper libraries (name ``drm_foo_helper_funcs``), which are purely for
136 internal use. Some of these hooks should be move from ``_funcs`` to
137 ``_helper_funcs`` since they are not part of the core ABI. There's a
138 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
139
140* There's a new helper ``drm_atomic_helper_best_encoder()`` which could be
141 used by all atomic drivers which don't select the encoder for a given
142 connector at runtime. That's almost all of them, and would allow us to get
143 rid of a lot of ``best_encoder`` boilerplate in drivers.
144
145 This was almost done, but new drivers added a few more cases again.
146
147Contact: Daniel Vetter
148
149Get rid of dev->struct_mutex from GEM drivers
150---------------------------------------------
151
152``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
153everything. Nowadays in modern drivers the only bit where it's mandatory is
154serializing GEM buffer object destruction. Which unfortunately means drivers
155have to keep track of that lock and either call ``unreference`` or
156``unreference_locked`` depending upon context.
157
158Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
159and there's a ``gem_free_object_unlocked`` callback for any drivers which are
160entirely ``struct_mutex`` free.
161
162For drivers that need ``struct_mutex`` it should be replaced with a driver-
163private lock. The tricky part is the BO free functions, since those can't
164reliably take that lock any more. Instead state needs to be protected with
165suitable subordinate locks or some cleanup work pushed to a worker thread. For
166performance-critical drivers it might also be better to go with a more
167fine-grained per-buffer object and per-context lockings scheme. Currently the
168following drivers still use ``struct_mutex``: ``msm``, ``omapdrm`` and
169``udl``.
170
171Contact: Daniel Vetter, respective driver maintainers
172
173Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent
174----------------------------------------------------------------------------
175
176For drivers which could have multiple instances, it is necessary to
177differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
178don't do this, drivers used dev_info/warn/err to make this differentiation. We
179now have DRM_DEV_* variants of the drm print macros, so we can start to convert
180those drivers back to using drm-formwatted specific log messages.
181
182Before you start this conversion please contact the relevant maintainers to make
183sure your work will be merged - not everyone agrees that the DRM dmesg macros
184are better.
185
186Contact: Sean Paul, Maintainer of the driver you plan to convert
187
188Convert drivers to use simple modeset suspend/resume
189----------------------------------------------------
190
191Most drivers (except i915 and nouveau) that use
192drm_atomic_helper_suspend/resume() can probably be converted to use
193drm_mode_config_helper_suspend/resume().
194
195Contact: Maintainer of the driver you plan to convert
196
197Convert drivers to use drm_fb_helper_fbdev_setup/teardown()
198-----------------------------------------------------------
199
200Most drivers can use drm_fb_helper_fbdev_setup() except maybe:
201
202- amdgpu which has special logic to decide whether to call
203 drm_helper_disable_unused_functions()
204
205- armada which isn't atomic and doesn't call
206 drm_helper_disable_unused_functions()
207
208- i915 which calls drm_fb_helper_initial_config() in a worker
209
210Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can
211probably use drm_fb_helper_fbdev_teardown().
212
213Contact: Maintainer of the driver you plan to convert
214
215idr_init_base()
216---------------
217
218DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
219userspace IDs to internal objects, and in most places ID=0 means NULL and hence
220is never used. Switching to idr_init_base() for these would make the idr more
221efficient.
222
223Contact: Daniel Vetter
224
225Core refactorings
226=================
227
228Clean up the DRM header mess
229----------------------------
230
231Currently the DRM subsystem has only one global header, ``drmP.h``. This is
232used both for functions exported to helper libraries and drivers and functions
233only used internally in the ``drm.ko`` module. The goal would be to move all
234header declarations not needed outside of ``drm.ko`` into
235``drivers/gpu/drm/drm_*_internal.h`` header files. ``EXPORT_SYMBOL`` also
236needs to be dropped for these functions.
237
238This would nicely tie in with the below task to create kerneldoc after the API
239is cleaned up. Or with the "hide legacy cruft better" task.
240
241Note that this is well in progress, but ``drmP.h`` is still huge. The updated
242plan is to switch to per-file driver API headers, which will also structure
243the kerneldoc better. This should also allow more fine-grained ``#include``
244directives.
245
246In the end no .c file should need to include ``drmP.h`` anymore.
247
248Contact: Daniel Vetter
249
250Add missing kerneldoc for exported functions
251--------------------------------------------
252
253The DRM reference documentation is still lacking kerneldoc in a few areas. The
254task would be to clean up interfaces like moving functions around between
255files to better group them and improving the interfaces like dropping return
256values for functions that never fail. Then write kerneldoc for all exported
257functions and an overview section and integrate it all into the drm book.
258
259See https://dri.freedesktop.org/docs/drm/ for what's there already.
260
261Contact: Daniel Vetter
262
263Hide legacy cruft better
264------------------------
265
266Way back DRM supported only drivers which shadow-attached to PCI devices with
267userspace or fbdev drivers setting up outputs. Modern DRM drivers take charge
268of the entire device, you can spot them with the DRIVER_MODESET flag.
269
270Unfortunately there's still large piles of legacy code around which needs to
271be hidden so that driver writers don't accidentally end up using it. And to
272prevent security issues in those legacy IOCTLs from being exploited on modern
273drivers. This has multiple possible subtasks:
274
275* Extract support code for legacy features into a ``drm-legacy.ko`` kernel
276 module and compile it only when one of the legacy drivers is enabled.
277
278This is mostly done, the only thing left is to split up ``drm_irq.c`` into
279legacy cruft and the parts needed by modern KMS drivers.
280
281Contact: Daniel Vetter
282
283Make panic handling work
284------------------------
285
286This is a really varied tasks with lots of little bits and pieces:
287
288* The panic path can't be tested currently, leading to constant breaking. The
289 main issue here is that panics can be triggered from hardirq contexts and
290 hence all panic related callback can run in hardirq context. It would be
291 awesome if we could test at least the fbdev helper code and driver code by
292 e.g. trigger calls through drm debugfs files. hardirq context could be
293 achieved by using an IPI to the local processor.
294
295* There's a massive confusion of different panic handlers. DRM fbdev emulation
296 helpers have one, but on top of that the fbcon code itself also has one. We
297 need to make sure that they stop fighting over each another.
298
299* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
300 isn't a full solution for panic paths. We need to make sure that it only
301 returns true if there's a panic going on for real, and fix up all the
302 fallout.
303
304* The panic handler must never sleep, which also means it can't ever
305 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
306 even spinlocks (because NMI and hardirq can panic too). We need to either
307 make sure to not call such paths, or trylock everything. Really tricky.
308
309* For the above locking troubles reasons it's pretty much impossible to
310 attempt a synchronous modeset from panic handlers. The only thing we could
311 try to achive is an atomic ``set_base`` of the primary plane, and hope that
312 it shows up. Everything else probably needs to be delayed to some worker or
313 something else which happens later on. Otherwise it just kills the box
314 harder, prevent the panic from going out on e.g. netconsole.
315
316* There's also proposal for a simplied DRM console instead of the full-blown
317 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
318 obviously work for both console, in case we ever get kmslog merged.
319
320Contact: Daniel Vetter
321
322Clean up the debugfs support
323----------------------------
324
325There's a bunch of issues with it:
326
327- The drm_info_list ->show() function doesn't even bother to cast to the drm
328 structure for you. This is lazy.
329
330- We probably want to have some support for debugfs files on crtc/connectors and
331 maybe other kms objects directly in core. There's even drm_print support in
332 the funcs for these objects to dump kms state, so it's all there. And then the
333 ->show() functions should obviously give you a pointer to the right object.
334
335- The drm_info_list stuff is centered on drm_minor instead of drm_device. For
336 anything we want to print drm_device (or maybe drm_file) is the right thing.
337
338- The drm_driver->debugfs_init hooks we have is just an artifact of the old
339 midlayered load sequence. DRM debugfs should work more like sysfs, where you
340 can create properties/files for an object anytime you want, and the core
341 takes care of publishing/unpuplishing all the files at register/unregister
342 time. Drivers shouldn't need to worry about these technicalities, and fixing
343 this (together with the drm_minor->drm_device move) would allow us to remove
344 debugfs_init.
345
346Contact: Daniel Vetter
347
348KMS cleanups
349------------
350
351Some of these date from the very introduction of KMS in 2008 ...
352
353- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should
354 be renamed to drm_mode_config.object_idr.
355
356- drm_display_mode doesn't need to be derived from drm_mode_object. That's
357 leftovers from older (never merged into upstream) KMS designs where modes
358 where set using their ID, including support to add/remove modes.
359
360Better Testing
361==============
362
363Enable trinity for DRM
364----------------------
365
366And fix up the fallout. Should be really interesting ...
367
368Make KMS tests in i-g-t generic
369-------------------------------
370
371The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
372including tons of testcases for corner-cases in the modesetting API. It would
373be awesome if those tests (at least the ones not relying on Intel-specific GEM
374features) could be made to run on any KMS driver.
375
376Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
377converting things over. For modeset tests we also first need a bit of
378infrastructure to use dumb buffers for untiled buffers, to be able to run all
379the non-i915 specific modeset tests.
380
381Contact: Daniel Vetter
382
383Create a virtual KMS driver for testing (vkms)
384----------------------------------------------
385
386With all the latest helpers it should be fairly simple to create a virtual KMS
387driver useful for testing, or for running X or similar on headless machines
388(to be able to still use the GPU). This would be similar to vgem, but aimed at
389the modeset side.
390
391Once the basics are there there's tons of possibilities to extend it.
392
393Contact: Daniel Vetter
394
395Driver Specific
396===============
397
398tinydrm
399-------
400
401Tinydrm is the helper driver for really simple fb drivers. The goal is to make
402those drivers as simple as possible, so lots of room for refactoring:
403
404- backlight helpers, probably best to put them into a new drm_backlight.c.
405 This is because drivers/video is de-facto unmaintained. We could also
406 move drivers/video/backlight to drivers/gpu/backlight and take it all
407 over within drm-misc, but that's more work. Backlight helpers require a fair
408 bit of reworking and refactoring. A simple example is the enabling of a backlight.
409 Tinydrm has helpers for this. It would be good if other drivers can also use the
410 helper. However, there are various cases we need to consider i.e different
411 drivers seem to have different ways of enabling/disabling a backlight.
412 We also need to consider the backlight drivers (like gpio_backlight). The situation
413 is further complicated by the fact that the backlight is tied to fbdev
414 via fb_notifier_callback() which has complicated logic. For further details, refer
415 to the following discussion thread:
416 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA
417
418- spi helpers, probably best put into spi core/helper code. Thierry said
419 the spi maintainer is fast&reactive, so shouldn't be a big issue.
420
421- extract the mipi-dbi helper (well, the non-tinydrm specific parts at
422 least) into a separate helper, like we have for mipi-dsi already. Or follow
423 one of the ideas for having a shared dsi/dbi helper, abstracting away the
424 transport details more.
425
426- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma
427 helpers, as a _vmapped variant (since not every driver needs the vmap).
428 And tinydrm_gem_cma_free_object could the be merged into
429 drm_gem_cma_free_object().
430
431- tinydrm_fb_create we could move into drm_simple_pipe, only need to add
432 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a
433 bunch of things (since it gives you a one-stop vfunc for simple drivers).
434
435- Quick aside: The unregister devm stuff is kinda getting the lifetimes of
436 a drm_device wrong. Doesn't matter, since everyone else gets it wrong
437 too :-)
438
439- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above.
440
441Contact: Noralf Trønnes, Daniel Vetter
442
443AMD DC Display Driver
444---------------------
445
446AMD DC is the display driver for AMD devices starting with Vega. There has been
447a bunch of progress cleaning it up but there's still plenty of work to be done.
448
449See drivers/gpu/drm/amd/display/TODO for tasks.
450
451Contact: Harry Wentland, Alex Deucher
452
453i915
454----
455
456- Our early/late pm callbacks could be removed in favour of using
457 device_link_add to model the dependency between i915 and snd_had. See
458 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html
459
460Outside DRM
461===========