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18implementation (there's lots of outdated locking leftovers in various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34implementation (there's lots of outdated locking leftovers in various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