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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
10Subsystem-wide refactorings
11===========================
12
13Remove custom dumb_map_offset implementations
14---------------------------------------------
15
16All GEM based drivers should be using drm_gem_create_mmap_offset() instead.
17Audit each individual driver, make sure it'll work with the generic
18implementation (there's lots of outdated locking leftovers in various
19implementations), and then remove it.
20
21Contact: Daniel Vetter, respective driver maintainers
22
23Convert existing KMS drivers to atomic modesetting
24--------------------------------------------------
25
263.19 has the atomic modeset interfaces and helpers, so drivers can now be
27converted over. Modern compositors like Wayland or Surfaceflinger on Android
28really want an atomic modeset interface, so this is all about the bright
29future.
30
31There is a conversion guide for atomic and all you need is a GPU for a
32non-converted driver (again virtual HW drivers for KVM are still all
33suitable).
34
35As part of this drivers also need to convert to universal plane (which means
36exposing primary & cursor as proper plane objects). But that's much easier to
37do by directly using the new atomic helper driver callbacks.
38
39Contact: Daniel Vetter, respective driver maintainers
40
41Clean up the clipped coordination confusion around planes
42---------------------------------------------------------
43
44We have a helper to get this right with drm_plane_helper_check_update(), but
45it's not consistently used. This should be fixed, preferrably in the atomic
46helpers (and drivers then moved over to clipped coordinates). Probably the
47helper should also be moved from drm_plane_helper.c to the atomic helpers, to
48avoid confusion - the other helpers in that file are all deprecated legacy
49helpers.
50
51Contact: Ville Syrjälä, Daniel Vetter, driver maintainers
52
53Convert early atomic drivers to async commit helpers
54----------------------------------------------------
55
56For the first year the atomic modeset helpers didn't support asynchronous /
57nonblocking commits, and every driver had to hand-roll them. This is fixed
58now, but there's still a pile of existing drivers that easily could be
59converted over to the new infrastructure.
60
61One issue with the helpers is that they require that drivers handle completion
62events for atomic commits correctly. But fixing these bugs is good anyway.
63
64Contact: Daniel Vetter, respective driver maintainers
65
66Fallout from atomic KMS
67-----------------------
68
69``drm_atomic_helper.c`` provides a batch of functions which implement legacy
70IOCTLs on top of the new atomic driver interface. Which is really nice for
71gradual conversion of drivers, but unfortunately the semantic mismatches are
72a bit too severe. So there's some follow-up work to adjust the function
73interfaces to fix these issues:
74
75* atomic needs the lock acquire context. At the moment that's passed around
76 implicitly with some horrible hacks, and it's also allocate with
77 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
78 the acquire context explicitly on stack and then also pass it down into
79 drivers explicitly so that the legacy-on-atomic functions can use them.
80
81 Except for some driver code this is done. This task should be finished by
82 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
83
84* A bunch of the vtable hooks are now in the wrong place: DRM has a split
85 between core vfunc tables (named ``drm_foo_funcs``), which are used to
86 implement the userspace ABI. And then there's the optional hooks for the
87 helper libraries (name ``drm_foo_helper_funcs``), which are purely for
88 internal use. Some of these hooks should be move from ``_funcs`` to
89 ``_helper_funcs`` since they are not part of the core ABI. There's a
90 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
91
92Contact: Daniel Vetter
93
94Get rid of dev->struct_mutex from GEM drivers
95---------------------------------------------
96
97``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
98everything. Nowadays in modern drivers the only bit where it's mandatory is
99serializing GEM buffer object destruction. Which unfortunately means drivers
100have to keep track of that lock and either call ``unreference`` or
101``unreference_locked`` depending upon context.
102
103Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
104and there's a ``gem_free_object_unlocked`` callback for any drivers which are
105entirely ``struct_mutex`` free.
106
107For drivers that need ``struct_mutex`` it should be replaced with a driver-
108private lock. The tricky part is the BO free functions, since those can't
109reliably take that lock any more. Instead state needs to be protected with
110suitable subordinate locks or some cleanup work pushed to a worker thread. For
111performance-critical drivers it might also be better to go with a more
112fine-grained per-buffer object and per-context lockings scheme. Currently only the
113``msm`` driver still use ``struct_mutex``.
114
115Contact: Daniel Vetter, respective driver maintainers
116
117Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent
118----------------------------------------------------------------------------
119
120For drivers which could have multiple instances, it is necessary to
121differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
122don't do this, drivers used dev_info/warn/err to make this differentiation. We
123now have DRM_DEV_* variants of the drm print macros, so we can start to convert
124those drivers back to using drm-formwatted specific log messages.
125
126Before you start this conversion please contact the relevant maintainers to make
127sure your work will be merged - not everyone agrees that the DRM dmesg macros
128are better.
129
130Contact: Sean Paul, Maintainer of the driver you plan to convert
131
132Convert drivers to use simple modeset suspend/resume
133----------------------------------------------------
134
135Most drivers (except i915 and nouveau) that use
136drm_atomic_helper_suspend/resume() can probably be converted to use
137drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
138of the atomic suspend/resume code in older atomic modeset drivers.
139
140Contact: Maintainer of the driver you plan to convert
141
142Convert drivers to use drm_fb_helper_fbdev_setup/teardown()
143-----------------------------------------------------------
144
145Most drivers can use drm_fb_helper_fbdev_setup() except maybe:
146
147- amdgpu which has special logic to decide whether to call
148 drm_helper_disable_unused_functions()
149
150- armada which isn't atomic and doesn't call
151 drm_helper_disable_unused_functions()
152
153- i915 which calls drm_fb_helper_initial_config() in a worker
154
155Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can
156probably use drm_fb_helper_fbdev_teardown().
157
158Contact: Maintainer of the driver you plan to convert
159
160Clean up mmap forwarding
161------------------------
162
163A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
164And also a lot of them forward dma-buf mmap to the gem mmap implementations.
165There's drm_gem_prime_mmap() for this now, but still needs to be rolled out.
166
167Contact: Daniel Vetter
168
169Generic fbdev defio support
170---------------------------
171
172The defio support code in the fbdev core has some very specific requirements,
173which means drivers need to have a special framebuffer for fbdev. Which prevents
174us from using the generic fbdev emulation code everywhere. The main issue is
175that it uses some fields in struct page itself, which breaks shmem gem objects
176(and other things).
177
178Possible solution would be to write our own defio mmap code in the drm fbdev
179emulation. It would need to fully wrap the existing mmap ops, forwarding
180everything after it has done the write-protect/mkwrite trickery:
181
182- In the drm_fbdev_fb_mmap helper, if we need defio, change the
183 default page prots to write-protected with something like this::
184
185 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot);
186
187- Set the mkwrite and fsync callbacks with similar implementions to the core
188 fbdev defio stuff. These should all work on plain ptes, they don't actually
189 require a struct page. uff. These should all work on plain ptes, they don't
190 actually require a struct page.
191
192- Track the dirty pages in a separate structure (bitfield with one bit per page
193 should work) to avoid clobbering struct page.
194
195Might be good to also have some igt testcases for this.
196
197Contact: Daniel Vetter, Noralf Tronnes
198
199idr_init_base()
200---------------
201
202DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
203userspace IDs to internal objects, and in most places ID=0 means NULL and hence
204is never used. Switching to idr_init_base() for these would make the idr more
205efficient.
206
207Contact: Daniel Vetter
208
209struct drm_gem_object_funcs
210---------------------------
211
212GEM objects can now have a function table instead of having the callbacks on the
213DRM driver struct. This is now the preferred way and drivers can be moved over.
214
215We also need a 2nd version of the CMA define that doesn't require the
216vmapping to be present (different hook for prime importing). Plus this needs to
217be rolled out to all drivers using their own implementations, too.
218
219Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate
220---------------------------------------------------------
221
222For cases where drivers are attempting to grab the modeset locks with a local
223acquire context. Replace the boilerplate code surrounding
224drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and
225DRM_MODESET_LOCK_ALL_END() instead.
226
227This should also be done for all places where drm_modest_lock_all() is still
228used.
229
230As a reference, take a look at the conversions already completed in drm core.
231
232Contact: Sean Paul, respective driver maintainers
233
234Rename CMA helpers to DMA helpers
235---------------------------------
236
237CMA (standing for contiguous memory allocator) is really a bit an accident of
238what these were used for first, a much better name would be DMA helpers. In the
239text these should even be called coherent DMA memory helpers (so maybe CDM, but
240no one knows what that means) since underneath they just use dma_alloc_coherent.
241
242Contact: Laurent Pinchart, Daniel Vetter
243
244Convert direct mode.vrefresh accesses to use drm_mode_vrefresh()
245----------------------------------------------------------------
246
247drm_display_mode.vrefresh isn't guaranteed to be populated. As such, using it
248is risky and has been known to cause div-by-zero bugs. Fortunately, drm core
249has helper which will use mode.vrefresh if it's !0 and will calculate it from
250the timings when it's 0.
251
252Use simple search/replace, or (more fun) cocci to replace instances of direct
253vrefresh access with a call to the helper. Check out
254https://lists.freedesktop.org/archives/dri-devel/2019-January/205186.html for
255inspiration.
256
257Once all instances of vrefresh have been converted, remove vrefresh from
258drm_display_mode to avoid future use.
259
260Contact: Sean Paul
261
262Remove drm_display_mode.hsync
263-----------------------------
264
265We have drm_mode_hsync() to calculate this from hsync_start/end, since drivers
266shouldn't/don't use this, remove this member to avoid any temptations to use it
267in the future. If there is any debug code using drm_display_mode.hsync, convert
268it to use drm_mode_hsync() instead.
269
270Contact: Sean Paul
271
272drm_fb_helper tasks
273-------------------
274
275- drm_fb_helper_restore_fbdev_mode_unlocked() should call restore_fbdev_mode()
276 not the _force variant so it can bail out if there is a master. But first
277 these igt tests need to be fixed: kms_fbcon_fbt@psr and
278 kms_fbcon_fbt@psr-suspend.
279
280- The max connector argument for drm_fb_helper_init() and
281 drm_fb_helper_fbdev_setup() isn't used anymore and can be removed.
282
283- The helper doesn't keep an array of connectors anymore so these can be
284 removed: drm_fb_helper_single_add_all_connectors(),
285 drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector().
286
287Core refactorings
288=================
289
290Clean up the DRM header mess
291----------------------------
292
293The DRM subsystem originally had only one huge global header, ``drmP.h``. This
294is now split up, but many source files still include it. The remaining part of
295the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the
296headers needed (and fixing up any missing pre-declarations in the headers).
297
298In the end no .c file should need to include ``drmP.h`` anymore.
299
300Contact: Daniel Vetter
301
302Make panic handling work
303------------------------
304
305This is a really varied tasks with lots of little bits and pieces:
306
307* The panic path can't be tested currently, leading to constant breaking. The
308 main issue here is that panics can be triggered from hardirq contexts and
309 hence all panic related callback can run in hardirq context. It would be
310 awesome if we could test at least the fbdev helper code and driver code by
311 e.g. trigger calls through drm debugfs files. hardirq context could be
312 achieved by using an IPI to the local processor.
313
314* There's a massive confusion of different panic handlers. DRM fbdev emulation
315 helpers have one, but on top of that the fbcon code itself also has one. We
316 need to make sure that they stop fighting over each another.
317
318* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
319 isn't a full solution for panic paths. We need to make sure that it only
320 returns true if there's a panic going on for real, and fix up all the
321 fallout.
322
323* The panic handler must never sleep, which also means it can't ever
324 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
325 even spinlocks (because NMI and hardirq can panic too). We need to either
326 make sure to not call such paths, or trylock everything. Really tricky.
327
328* For the above locking troubles reasons it's pretty much impossible to
329 attempt a synchronous modeset from panic handlers. The only thing we could
330 try to achive is an atomic ``set_base`` of the primary plane, and hope that
331 it shows up. Everything else probably needs to be delayed to some worker or
332 something else which happens later on. Otherwise it just kills the box
333 harder, prevent the panic from going out on e.g. netconsole.
334
335* There's also proposal for a simplied DRM console instead of the full-blown
336 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
337 obviously work for both console, in case we ever get kmslog merged.
338
339Contact: Daniel Vetter
340
341Clean up the debugfs support
342----------------------------
343
344There's a bunch of issues with it:
345
346- The drm_info_list ->show() function doesn't even bother to cast to the drm
347 structure for you. This is lazy.
348
349- We probably want to have some support for debugfs files on crtc/connectors and
350 maybe other kms objects directly in core. There's even drm_print support in
351 the funcs for these objects to dump kms state, so it's all there. And then the
352 ->show() functions should obviously give you a pointer to the right object.
353
354- The drm_info_list stuff is centered on drm_minor instead of drm_device. For
355 anything we want to print drm_device (or maybe drm_file) is the right thing.
356
357- The drm_driver->debugfs_init hooks we have is just an artifact of the old
358 midlayered load sequence. DRM debugfs should work more like sysfs, where you
359 can create properties/files for an object anytime you want, and the core
360 takes care of publishing/unpuplishing all the files at register/unregister
361 time. Drivers shouldn't need to worry about these technicalities, and fixing
362 this (together with the drm_minor->drm_device move) would allow us to remove
363 debugfs_init.
364
365- Drop the return code and error checking from all debugfs functions. Greg KH is
366 working on this already.
367
368Contact: Daniel Vetter
369
370KMS cleanups
371------------
372
373Some of these date from the very introduction of KMS in 2008 ...
374
375- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
376 function tables in drivers, but before we can remove them we need to make sure
377 that all the users in helpers and drivers do correctly check for a NULL
378 vtable.
379
380- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
381 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
382 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
383 historical reasons) misnamed drm_primary_helper_destroy() function.
384
385Better Testing
386==============
387
388Enable trinity for DRM
389----------------------
390
391And fix up the fallout. Should be really interesting ...
392
393Make KMS tests in i-g-t generic
394-------------------------------
395
396The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
397including tons of testcases for corner-cases in the modesetting API. It would
398be awesome if those tests (at least the ones not relying on Intel-specific GEM
399features) could be made to run on any KMS driver.
400
401Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
402converting things over. For modeset tests we also first need a bit of
403infrastructure to use dumb buffers for untiled buffers, to be able to run all
404the non-i915 specific modeset tests.
405
406Extend virtual test driver (VKMS)
407---------------------------------
408
409See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
410internship task, since it only requires a virtual machine and can be sized to
411fit the available time.
412
413Contact: Daniel Vetter
414
415Backlight Refactoring
416---------------------
417
418Backlight drivers have a triple enable/disable state, which is a bit overkill.
419Plan to fix this:
420
4211. Roll out backlight_enable() and backlight_disable() helpers everywhere. This
422 has started already.
4232. In all, only look at one of the three status bits set by the above helpers.
4243. Remove the other two status bits.
425
426Contact: Daniel Vetter
427
428Driver Specific
429===============
430
431AMD DC Display Driver
432---------------------
433
434AMD DC is the display driver for AMD devices starting with Vega. There has been
435a bunch of progress cleaning it up but there's still plenty of work to be done.
436
437See drivers/gpu/drm/amd/display/TODO for tasks.
438
439Contact: Harry Wentland, Alex Deucher
440
441i915
442----
443
444- Our early/late pm callbacks could be removed in favour of using
445 device_link_add to model the dependency between i915 and snd_had. See
446 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html
447
448Bootsplash
449==========
450
451There is support in place now for writing internal DRM clients making it
452possible to pick up the bootsplash work that was rejected because it was written
453for fbdev.
454
455- [v6,8/8] drm/client: Hack: Add bootsplash example
456 https://patchwork.freedesktop.org/patch/306579/
457
458- [RFC PATCH v2 00/13] Kernel based bootsplash
459 https://lkml.org/lkml/2017/12/13/764
460
461Contact: Sam Ravnborg
462
463Outside DRM
464===========
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: Daniel 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 and all you need is a GPU for a
53non-converted driver (again virtual HW drivers for KVM are still all
54suitable).
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
60Contact: Daniel Vetter, respective driver maintainers
61
62Level: Advanced
63
64Clean up the clipped coordination confusion around planes
65---------------------------------------------------------
66
67We have a helper to get this right with drm_plane_helper_check_update(), but
68it's not consistently used. This should be fixed, preferrably in the atomic
69helpers (and drivers then moved over to clipped coordinates). Probably the
70helper should also be moved from drm_plane_helper.c to the atomic helpers, to
71avoid confusion - the other helpers in that file are all deprecated legacy
72helpers.
73
74Contact: Ville Syrjälä, Daniel Vetter, driver maintainers
75
76Level: Advanced
77
78Improve plane atomic_check helpers
79----------------------------------
80
81Aside from the clipped coordinates right above there's a few suboptimal things
82with the current helpers:
83
84- drm_plane_helper_funcs->atomic_check gets called for enabled or disabled
85 planes. At best this seems to confuse drivers, worst it means they blow up
86 when the plane is disabled without the CRTC. The only special handling is
87 resetting values in the plane state structures, which instead should be moved
88 into the drm_plane_funcs->atomic_duplicate_state functions.
89
90- Once that's done, helpers could stop calling ->atomic_check for disabled
91 planes.
92
93- Then we could go through all the drivers and remove the more-or-less confused
94 checks for plane_state->fb and plane_state->crtc.
95
96Contact: Daniel Vetter
97
98Level: Advanced
99
100Convert early atomic drivers to async commit helpers
101----------------------------------------------------
102
103For the first year the atomic modeset helpers didn't support asynchronous /
104nonblocking commits, and every driver had to hand-roll them. This is fixed
105now, but there's still a pile of existing drivers that easily could be
106converted over to the new infrastructure.
107
108One issue with the helpers is that they require that drivers handle completion
109events for atomic commits correctly. But fixing these bugs is good anyway.
110
111Somewhat related is the legacy_cursor_update hack, which should be replaced with
112the new atomic_async_check/commit functionality in the helpers in drivers that
113still look at that flag.
114
115Contact: Daniel Vetter, respective driver maintainers
116
117Level: Advanced
118
119Fallout from atomic KMS
120-----------------------
121
122``drm_atomic_helper.c`` provides a batch of functions which implement legacy
123IOCTLs on top of the new atomic driver interface. Which is really nice for
124gradual conversion of drivers, but unfortunately the semantic mismatches are
125a bit too severe. So there's some follow-up work to adjust the function
126interfaces to fix these issues:
127
128* atomic needs the lock acquire context. At the moment that's passed around
129 implicitly with some horrible hacks, and it's also allocate with
130 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
131 the acquire context explicitly on stack and then also pass it down into
132 drivers explicitly so that the legacy-on-atomic functions can use them.
133
134 Except for some driver code this is done. This task should be finished by
135 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
136
137* A bunch of the vtable hooks are now in the wrong place: DRM has a split
138 between core vfunc tables (named ``drm_foo_funcs``), which are used to
139 implement the userspace ABI. And then there's the optional hooks for the
140 helper libraries (name ``drm_foo_helper_funcs``), which are purely for
141 internal use. Some of these hooks should be move from ``_funcs`` to
142 ``_helper_funcs`` since they are not part of the core ABI. There's a
143 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
144
145Contact: Daniel Vetter
146
147Level: Intermediate
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 object ``free`` 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 only
168the ``msm`` and `i915` drivers use ``struct_mutex``.
169
170Contact: Daniel Vetter, respective driver maintainers
171
172Level: Advanced
173
174Move Buffer Object Locking to dma_resv_lock()
175---------------------------------------------
176
177Many drivers have their own per-object locking scheme, usually using
178mutex_lock(). This causes all kinds of trouble for buffer sharing, since
179depending which driver is the exporter and importer, the locking hierarchy is
180reversed.
181
182To solve this we need one standard per-object locking mechanism, which is
183dma_resv_lock(). This lock needs to be called as the outermost lock, with all
184other driver specific per-object locks removed. The problem is tha rolling out
185the actual change to the locking contract is a flag day, due to struct dma_buf
186buffer sharing.
187
188Level: Expert
189
190Convert logging to drm_* functions with drm_device paramater
191------------------------------------------------------------
192
193For drivers which could have multiple instances, it is necessary to
194differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
195don't do this, drivers used dev_info/warn/err to make this differentiation. We
196now have drm_* variants of the drm print functions, so we can start to convert
197those drivers back to using drm-formatted specific log messages.
198
199Before you start this conversion please contact the relevant maintainers to make
200sure your work will be merged - not everyone agrees that the DRM dmesg macros
201are better.
202
203Contact: Sean Paul, Maintainer of the driver you plan to convert
204
205Level: Starter
206
207Convert drivers to use simple modeset suspend/resume
208----------------------------------------------------
209
210Most drivers (except i915 and nouveau) that use
211drm_atomic_helper_suspend/resume() can probably be converted to use
212drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
213of the atomic suspend/resume code in older atomic modeset drivers.
214
215Contact: Maintainer of the driver you plan to convert
216
217Level: Intermediate
218
219Convert drivers to use drm_fbdev_generic_setup()
220------------------------------------------------
221
222Most drivers can use drm_fbdev_generic_setup(). Driver have to implement
223atomic modesetting and GEM vmap support. Historically, generic fbdev emulation
224expected the framebuffer in system memory or system-like memory. By employing
225struct dma_buf_map, drivers with frambuffers in I/O memory can be supported
226as well.
227
228Contact: Maintainer of the driver you plan to convert
229
230Level: Intermediate
231
232Reimplement functions in drm_fbdev_fb_ops without fbdev
233-------------------------------------------------------
234
235A number of callback functions in drm_fbdev_fb_ops could benefit from
236being rewritten without dependencies on the fbdev module. Some of the
237helpers could further benefit from using struct dma_buf_map instead of
238raw pointers.
239
240Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter
241
242Level: Advanced
243
244
245drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup
246-----------------------------------------------------------------
247
248A lot more drivers could be switched over to the drm_gem_framebuffer helpers.
249Various hold-ups:
250
251- Need to switch over to the generic dirty tracking code using
252 drm_atomic_helper_dirtyfb first (e.g. qxl).
253
254- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb
255 setup code can't be deleted.
256
257- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For
258 atomic drivers we could check for valid formats by calling
259 drm_plane_check_pixel_format() against all planes, and pass if any plane
260 supports the format. For non-atomic that's not possible since like the format
261 list for the primary plane is fake and we'd therefor reject valid formats.
262
263- Many drivers subclass drm_framebuffer, we'd need a embedding compatible
264 version of the varios drm_gem_fb_create functions. Maybe called
265 drm_gem_fb_create/_with_dirty/_with_funcs as needed.
266
267Contact: Daniel Vetter
268
269Level: Intermediate
270
271Clean up mmap forwarding
272------------------------
273
274A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
275And also a lot of them forward dma-buf mmap to the gem mmap implementations.
276There's drm_gem_prime_mmap() for this now, but still needs to be rolled out.
277
278Contact: Daniel Vetter
279
280Level: Intermediate
281
282Generic fbdev defio support
283---------------------------
284
285The defio support code in the fbdev core has some very specific requirements,
286which means drivers need to have a special framebuffer for fbdev. The main
287issue is that it uses some fields in struct page itself, which breaks shmem
288gem objects (and other things). To support defio, affected drivers require
289the use of a shadow buffer, which may add CPU and memory overhead.
290
291Possible solution would be to write our own defio mmap code in the drm fbdev
292emulation. It would need to fully wrap the existing mmap ops, forwarding
293everything after it has done the write-protect/mkwrite trickery:
294
295- In the drm_fbdev_fb_mmap helper, if we need defio, change the
296 default page prots to write-protected with something like this::
297
298 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot);
299
300- Set the mkwrite and fsync callbacks with similar implementions to the core
301 fbdev defio stuff. These should all work on plain ptes, they don't actually
302 require a struct page. uff. These should all work on plain ptes, they don't
303 actually require a struct page.
304
305- Track the dirty pages in a separate structure (bitfield with one bit per page
306 should work) to avoid clobbering struct page.
307
308Might be good to also have some igt testcases for this.
309
310Contact: Daniel Vetter, Noralf Tronnes
311
312Level: Advanced
313
314Garbage collect fbdev scrolling acceleration
315--------------------------------------------
316
317Scroll acceleration is disabled in fbcon by hard-wiring p->scrollmode =
318SCROLL_REDRAW. There's a ton of code this will allow us to remove:
319
320- lots of code in fbcon.c
321
322- a bunch of the hooks in fbcon_ops, maybe the remaining hooks could be called
323 directly instead of the function table (with a switch on p->rotate)
324
325- fb_copyarea is unused after this, and can be deleted from all drivers
326
327Note that not all acceleration code can be deleted, since clearing and cursor
328support is still accelerated, which might be good candidates for further
329deletion projects.
330
331Contact: Daniel Vetter
332
333Level: Intermediate
334
335idr_init_base()
336---------------
337
338DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
339userspace IDs to internal objects, and in most places ID=0 means NULL and hence
340is never used. Switching to idr_init_base() for these would make the idr more
341efficient.
342
343Contact: Daniel Vetter
344
345Level: Starter
346
347struct drm_gem_object_funcs
348---------------------------
349
350GEM objects can now have a function table instead of having the callbacks on the
351DRM driver struct. This is now the preferred way. Callbacks in drivers have been
352converted, except for struct drm_driver.gem_prime_mmap.
353
354Level: Intermediate
355
356Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate
357---------------------------------------------------------
358
359For cases where drivers are attempting to grab the modeset locks with a local
360acquire context. Replace the boilerplate code surrounding
361drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and
362DRM_MODESET_LOCK_ALL_END() instead.
363
364This should also be done for all places where drm_modeset_lock_all() is still
365used.
366
367As a reference, take a look at the conversions already completed in drm core.
368
369Contact: Sean Paul, respective driver maintainers
370
371Level: Starter
372
373Rename CMA helpers to DMA helpers
374---------------------------------
375
376CMA (standing for contiguous memory allocator) is really a bit an accident of
377what these were used for first, a much better name would be DMA helpers. In the
378text these should even be called coherent DMA memory helpers (so maybe CDM, but
379no one knows what that means) since underneath they just use dma_alloc_coherent.
380
381Contact: Laurent Pinchart, Daniel Vetter
382
383Level: Intermediate (mostly because it is a huge tasks without good partial
384milestones, not technically itself that challenging)
385
386connector register/unregister fixes
387-----------------------------------
388
389- For most connectors it's a no-op to call drm_connector_register/unregister
390 directly from driver code, drm_dev_register/unregister take care of this
391 already. We can remove all of them.
392
393- For dp drivers it's a bit more a mess, since we need the connector to be
394 registered when calling drm_dp_aux_register. Fix this by instead calling
395 drm_dp_aux_init, and moving the actual registering into a late_register
396 callback as recommended in the kerneldoc.
397
398Level: Intermediate
399
400Remove load/unload callbacks from all non-DRIVER_LEGACY drivers
401---------------------------------------------------------------
402
403The load/unload callbacks in struct &drm_driver are very much midlayers, plus
404for historical reasons they get the ordering wrong (and we can't fix that)
405between setting up the &drm_driver structure and calling drm_dev_register().
406
407- Rework drivers to no longer use the load/unload callbacks, directly coding the
408 load/unload sequence into the driver's probe function.
409
410- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload
411 callbacks for all modern drivers.
412
413Contact: Daniel Vetter
414
415Level: Intermediate
416
417Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi
418---------------------------------------------------------------
419
420Once EDID is parsed, the monitor HDMI support information is available through
421drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to
422retrieve the same information, which is less efficient.
423
424Audit each individual driver calling drm_detect_hdmi_monitor() and switch to
425drm_display_info.is_hdmi if applicable.
426
427Contact: Laurent Pinchart, respective driver maintainers
428
429Level: Intermediate
430
431Consolidate custom driver modeset properties
432--------------------------------------------
433
434Before atomic modeset took place, many drivers where creating their own
435properties. Among other things, atomic brought the requirement that custom,
436driver specific properties should not be used.
437
438For this task, we aim to introduce core helpers or reuse the existing ones
439if available:
440
441A quick, unconfirmed, examples list.
442
443Introduce core helpers:
444- audio (amdgpu, intel, gma500, radeon)
445- brightness, contrast, etc (armada, nouveau) - overlay only (?)
446- broadcast rgb (gma500, intel)
447- colorkey (armada, nouveau, rcar) - overlay only (?)
448- dither (amdgpu, nouveau, radeon) - varies across drivers
449- underscan family (amdgpu, radeon, nouveau)
450
451Already in core:
452- colorspace (sti)
453- tv format names, enhancements (gma500, intel)
454- tv overscan, margins, etc. (gma500, intel)
455- zorder (omapdrm) - same as zpos (?)
456
457
458Contact: Emil Velikov, respective driver maintainers
459
460Level: Intermediate
461
462Use struct dma_buf_map throughout codebase
463------------------------------------------
464
465Pointers to shared device memory are stored in struct dma_buf_map. Each
466instance knows whether it refers to system or I/O memory. Most of the DRM-wide
467interface have been converted to use struct dma_buf_map, but implementations
468often still use raw pointers.
469
470The task is to use struct dma_buf_map where it makes sense.
471
472* Memory managers should use struct dma_buf_map for dma-buf-imported buffers.
473* TTM might benefit from using struct dma_buf_map internally.
474* Framebuffer copying and blitting helpers should operate on struct dma_buf_map.
475
476Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Daniel Vetter
477
478Level: Intermediate
479
480
481Core refactorings
482=================
483
484Make panic handling work
485------------------------
486
487This is a really varied tasks with lots of little bits and pieces:
488
489* The panic path can't be tested currently, leading to constant breaking. The
490 main issue here is that panics can be triggered from hardirq contexts and
491 hence all panic related callback can run in hardirq context. It would be
492 awesome if we could test at least the fbdev helper code and driver code by
493 e.g. trigger calls through drm debugfs files. hardirq context could be
494 achieved by using an IPI to the local processor.
495
496* There's a massive confusion of different panic handlers. DRM fbdev emulation
497 helpers have one, but on top of that the fbcon code itself also has one. We
498 need to make sure that they stop fighting over each another.
499
500* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
501 isn't a full solution for panic paths. We need to make sure that it only
502 returns true if there's a panic going on for real, and fix up all the
503 fallout.
504
505* The panic handler must never sleep, which also means it can't ever
506 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
507 even spinlocks (because NMI and hardirq can panic too). We need to either
508 make sure to not call such paths, or trylock everything. Really tricky.
509
510* For the above locking troubles reasons it's pretty much impossible to
511 attempt a synchronous modeset from panic handlers. The only thing we could
512 try to achive is an atomic ``set_base`` of the primary plane, and hope that
513 it shows up. Everything else probably needs to be delayed to some worker or
514 something else which happens later on. Otherwise it just kills the box
515 harder, prevent the panic from going out on e.g. netconsole.
516
517* There's also proposal for a simplied DRM console instead of the full-blown
518 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
519 obviously work for both console, in case we ever get kmslog merged.
520
521Contact: Daniel Vetter
522
523Level: Advanced
524
525Clean up the debugfs support
526----------------------------
527
528There's a bunch of issues with it:
529
530- The drm_info_list ->show() function doesn't even bother to cast to the drm
531 structure for you. This is lazy.
532
533- We probably want to have some support for debugfs files on crtc/connectors and
534 maybe other kms objects directly in core. There's even drm_print support in
535 the funcs for these objects to dump kms state, so it's all there. And then the
536 ->show() functions should obviously give you a pointer to the right object.
537
538- The drm_info_list stuff is centered on drm_minor instead of drm_device. For
539 anything we want to print drm_device (or maybe drm_file) is the right thing.
540
541- The drm_driver->debugfs_init hooks we have is just an artifact of the old
542 midlayered load sequence. DRM debugfs should work more like sysfs, where you
543 can create properties/files for an object anytime you want, and the core
544 takes care of publishing/unpuplishing all the files at register/unregister
545 time. Drivers shouldn't need to worry about these technicalities, and fixing
546 this (together with the drm_minor->drm_device move) would allow us to remove
547 debugfs_init.
548
549Previous RFC that hasn't landed yet: https://lore.kernel.org/dri-devel/20200513114130.28641-2-wambui.karugax@gmail.com/
550
551Contact: Daniel Vetter
552
553Level: Intermediate
554
555Object lifetime fixes
556---------------------
557
558There's two related issues here
559
560- Cleanup up the various ->destroy callbacks, which often are all the same
561 simple code.
562
563- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc,
564 which results in use-after free issues on driver unload. This can be serious
565 trouble even for drivers for hardware integrated on the SoC due to
566 EPROBE_DEFERRED backoff.
567
568Both these problems can be solved by switching over to drmm_kzalloc(), and the
569various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(),
570drmm_universal_plane_alloc(), ... and so on.
571
572Contact: Daniel Vetter
573
574Level: Intermediate
575
576Remove automatic page mapping from dma-buf importing
577----------------------------------------------------
578
579When importing dma-bufs, the dma-buf and PRIME frameworks automatically map
580imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and
581drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach()
582even if they never do actual device DMA, but only CPU access through
583dma_buf_vmap(). This is a problem for USB devices, which do not support DMA
584operations.
585
586To fix the issue, automatic page mappings should be removed from the
587buffer-sharing code. Fixing this is a bit more involved, since the import/export
588cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over
589this problem for USB devices by fishing out the USB host controller device, as
590long as that supports DMA. Otherwise importing can still needlessly fail.
591
592Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter
593
594Level: Advanced
595
596
597Better Testing
598==============
599
600Enable trinity for DRM
601----------------------
602
603And fix up the fallout. Should be really interesting ...
604
605Level: Advanced
606
607Make KMS tests in i-g-t generic
608-------------------------------
609
610The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
611including tons of testcases for corner-cases in the modesetting API. It would
612be awesome if those tests (at least the ones not relying on Intel-specific GEM
613features) could be made to run on any KMS driver.
614
615Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
616converting things over. For modeset tests we also first need a bit of
617infrastructure to use dumb buffers for untiled buffers, to be able to run all
618the non-i915 specific modeset tests.
619
620Level: Advanced
621
622Extend virtual test driver (VKMS)
623---------------------------------
624
625See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
626internship task, since it only requires a virtual machine and can be sized to
627fit the available time.
628
629Level: See details
630
631Backlight Refactoring
632---------------------
633
634Backlight drivers have a triple enable/disable state, which is a bit overkill.
635Plan to fix this:
636
6371. Roll out backlight_enable() and backlight_disable() helpers everywhere. This
638 has started already.
6392. In all, only look at one of the three status bits set by the above helpers.
6403. Remove the other two status bits.
641
642Contact: Daniel Vetter
643
644Level: Intermediate
645
646Driver Specific
647===============
648
649AMD DC Display Driver
650---------------------
651
652AMD DC is the display driver for AMD devices starting with Vega. There has been
653a bunch of progress cleaning it up but there's still plenty of work to be done.
654
655See drivers/gpu/drm/amd/display/TODO for tasks.
656
657Contact: Harry Wentland, Alex Deucher
658
659Bootsplash
660==========
661
662There is support in place now for writing internal DRM clients making it
663possible to pick up the bootsplash work that was rejected because it was written
664for fbdev.
665
666- [v6,8/8] drm/client: Hack: Add bootsplash example
667 https://patchwork.freedesktop.org/patch/306579/
668
669- [RFC PATCH v2 00/13] Kernel based bootsplash
670 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de
671
672Contact: Sam Ravnborg
673
674Level: Advanced
675
676Outside DRM
677===========
678
679Convert fbdev drivers to DRM
680----------------------------
681
682There are plenty of fbdev drivers for older hardware. Some hardware has
683become obsolete, but some still provides good(-enough) framebuffers. The
684drivers that are still useful should be converted to DRM and afterwards
685removed from fbdev.
686
687Very simple fbdev drivers can best be converted by starting with a new
688DRM driver. Simple KMS helpers and SHMEM should be able to handle any
689existing hardware. The new driver's call-back functions are filled from
690existing fbdev code.
691
692More complex fbdev drivers can be refactored step-by-step into a DRM
693driver with the help of the DRM fbconv helpers. [1] These helpers provide
694the transition layer between the DRM core infrastructure and the fbdev
695driver interface. Create a new DRM driver on top of the fbconv helpers,
696copy over the fbdev driver, and hook it up to the DRM code. Examples for
697several fbdev drivers are available at [1] and a tutorial of this process
698available at [2]. The result is a primitive DRM driver that can run X11
699and Weston.
700
701 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv
702 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c
703
704Contact: Thomas Zimmermann <tzimmermann@suse.de>
705
706Level: Advanced