7 This section contains a list of smaller janitorial tasks in the kernel DRM
8 graphics subsystem useful as newbie projects. Or for slow rainy days.
10 Subsystem-wide refactorings
11 ===========================
16 With the recent ``drm_bus`` cleanup patches for 3.17 it is no longer required
17 to have a ``drm_bus`` structure set up. Drivers can directly set up the
18 ``drm_device`` structure instead of relying on bus methods in ``drm_usb.c``
19 and ``drm_pci.c``. The goal is to get rid of the driver's ``->load`` /
20 ``->unload`` callbacks and open-code the load/unload sequence properly, using
21 the new two-stage ``drm_device`` setup/teardown.
23 Once all existing drivers are converted we can also remove those bus support
24 files for USB and platform devices.
26 All you need is a GPU for a non-converted driver (currently almost all of
27 them, but also all the virtual ones used by KVM, so everyone qualifies).
29 Contact: Daniel Vetter, Thierry Reding, respective driver maintainers
31 Switch from reference/unreference to get/put
32 --------------------------------------------
34 For some reason DRM core uses ``reference``/``unreference`` suffixes for
35 refcounting functions, but kernel uses ``get``/``put`` (e.g.
36 ``kref_get``/``put()``). It would be good to switch over for consistency, and
37 it's shorter. Needs to be done in 3 steps for each pair of functions:
39 * Create new ``get``/``put`` functions, define the old names as compatibility
41 * Switch over each file/driver using a cocci-generated spatch.
42 * Once all users of the old names are gone, remove them.
44 This way drivers/patches in the progress of getting merged won't break.
46 Contact: Daniel Vetter
48 Convert existing KMS drivers to atomic modesetting
49 --------------------------------------------------
51 3.19 has the atomic modeset interfaces and helpers, so drivers can now be
52 converted over. Modern compositors like Wayland or Surfaceflinger on Android
53 really want an atomic modeset interface, so this is all about the bright
56 There is a conversion guide for atomic and all you need is a GPU for a
57 non-converted driver (again virtual HW drivers for KVM are still all
60 As part of this drivers also need to convert to universal plane (which means
61 exposing primary & cursor as proper plane objects). But that's much easier to
62 do by directly using the new atomic helper driver callbacks.
64 Contact: Daniel Vetter, respective driver maintainers
66 Clean up the clipped coordination confusion around planes
67 ---------------------------------------------------------
69 We have a helper to get this right with drm_plane_helper_check_update(), but
70 it's not consistently used. This should be fixed, preferrably in the atomic
71 helpers (and drivers then moved over to clipped coordinates). Probably the
72 helper should also be moved from drm_plane_helper.c to the atomic helpers, to
73 avoid confusion - the other helpers in that file are all deprecated legacy
76 Contact: Ville Syrjälä, Daniel Vetter, driver maintainers
78 Convert early atomic drivers to async commit helpers
79 ----------------------------------------------------
81 For the first year the atomic modeset helpers didn't support asynchronous /
82 nonblocking commits, and every driver had to hand-roll them. This is fixed
83 now, but there's still a pile of existing drivers that easily could be
84 converted over to the new infrastructure.
86 One issue with the helpers is that they require that drivers handle completion
87 events for atomic commits correctly. But fixing these bugs is good anyway.
89 Contact: Daniel Vetter, respective driver maintainers
91 Better manual-upload support for atomic
92 ---------------------------------------
94 This would be especially useful for tinydrm:
96 - Add a struct drm_rect dirty_clip to drm_crtc_state. When duplicating the
97 crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in
98 __drm_atomic_helper_crtc_duplicate_state().
100 - Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_
101 prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this
102 is a function useful to implement the fb->dirty function.
104 - Create a new drm_fb_dirty function which does essentially what e.g.
105 mipi_dbi_fb_dirty does. You can use e.g. drm_atomic_helper_update_plane as the
106 template. But instead of doing a simple full-screen plane update, this new
107 helper also sets crtc_state->dirty_clip to the right coordinates. And of
108 course it needs to check whether the fb is actually active (and maybe where),
109 so there's some book-keeping involved. There's also some good fun involved in
110 scaling things appropriately. For that case we might simply give up and
111 declare the entire area covered by the plane as dirty.
113 Contact: Noralf Trønnes, Daniel Vetter
115 Fallout from atomic KMS
116 -----------------------
118 ``drm_atomic_helper.c`` provides a batch of functions which implement legacy
119 IOCTLs on top of the new atomic driver interface. Which is really nice for
120 gradual conversion of drivers, but unfortunately the semantic mismatches are
121 a bit too severe. So there's some follow-up work to adjust the function
122 interfaces to fix these issues:
124 * atomic needs the lock acquire context. At the moment that's passed around
125 implicitly with some horrible hacks, and it's also allocate with
126 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
127 the acquire context explicitly on stack and then also pass it down into
128 drivers explicitly so that the legacy-on-atomic functions can use them.
130 Except for some driver code this is done. This task should be finished by
131 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
133 * A bunch of the vtable hooks are now in the wrong place: DRM has a split
134 between core vfunc tables (named ``drm_foo_funcs``), which are used to
135 implement the userspace ABI. And then there's the optional hooks for the
136 helper libraries (name ``drm_foo_helper_funcs``), which are purely for
137 internal use. Some of these hooks should be move from ``_funcs`` to
138 ``_helper_funcs`` since they are not part of the core ABI. There's a
139 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
141 Contact: Daniel Vetter
143 Get rid of dev->struct_mutex from GEM drivers
144 ---------------------------------------------
146 ``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
147 everything. Nowadays in modern drivers the only bit where it's mandatory is
148 serializing GEM buffer object destruction. Which unfortunately means drivers
149 have to keep track of that lock and either call ``unreference`` or
150 ``unreference_locked`` depending upon context.
152 Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
153 and there's a ``gem_free_object_unlocked`` callback for any drivers which are
154 entirely ``struct_mutex`` free.
156 For drivers that need ``struct_mutex`` it should be replaced with a driver-
157 private lock. The tricky part is the BO free functions, since those can't
158 reliably take that lock any more. Instead state needs to be protected with
159 suitable subordinate locks or some cleanup work pushed to a worker thread. For
160 performance-critical drivers it might also be better to go with a more
161 fine-grained per-buffer object and per-context lockings scheme. Currently only the
162 ``msm`` driver still use ``struct_mutex``.
164 Contact: Daniel Vetter, respective driver maintainers
166 Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent
167 ----------------------------------------------------------------------------
169 For drivers which could have multiple instances, it is necessary to
170 differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
171 don't do this, drivers used dev_info/warn/err to make this differentiation. We
172 now have DRM_DEV_* variants of the drm print macros, so we can start to convert
173 those drivers back to using drm-formwatted specific log messages.
175 Before you start this conversion please contact the relevant maintainers to make
176 sure your work will be merged - not everyone agrees that the DRM dmesg macros
179 Contact: Sean Paul, Maintainer of the driver you plan to convert
181 Convert drivers to use simple modeset suspend/resume
182 ----------------------------------------------------
184 Most drivers (except i915 and nouveau) that use
185 drm_atomic_helper_suspend/resume() can probably be converted to use
186 drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
187 of the atomic suspend/resume code in older atomic modeset drivers.
189 Contact: Maintainer of the driver you plan to convert
191 Convert drivers to use drm_fb_helper_fbdev_setup/teardown()
192 -----------------------------------------------------------
194 Most drivers can use drm_fb_helper_fbdev_setup() except maybe:
196 - amdgpu which has special logic to decide whether to call
197 drm_helper_disable_unused_functions()
199 - armada which isn't atomic and doesn't call
200 drm_helper_disable_unused_functions()
202 - i915 which calls drm_fb_helper_initial_config() in a worker
204 Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can
205 probably use drm_fb_helper_fbdev_teardown().
207 Contact: Maintainer of the driver you plan to convert
209 Clean up mmap forwarding
210 ------------------------
212 A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
213 And also a lot of them forward dma-buf mmap to the gem mmap implementations.
214 Would be great to refactor this all into a set of small common helpers.
216 Contact: Daniel Vetter
218 Put a reservation_object into drm_gem_object
219 --------------------------------------------
221 This would remove the need for the ->gem_prime_res_obj callback. It would also
222 allow us to implement generic helpers for waiting for a bo, allowing for quite a
223 bit of refactoring in the various wait ioctl implementations.
225 Contact: Daniel Vetter
230 DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
231 userspace IDs to internal objects, and in most places ID=0 means NULL and hence
232 is never used. Switching to idr_init_base() for these would make the idr more
235 Contact: Daniel Vetter
240 Clean up the DRM header mess
241 ----------------------------
243 The DRM subsystem originally had only one huge global header, ``drmP.h``. This
244 is now split up, but many source files still include it. The remaining part of
245 the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the
246 headers needed (and fixing up any missing pre-declarations in the headers).
248 In the end no .c file should need to include ``drmP.h`` anymore.
250 Contact: Daniel Vetter
252 Add missing kerneldoc for exported functions
253 --------------------------------------------
255 The DRM reference documentation is still lacking kerneldoc in a few areas. The
256 task would be to clean up interfaces like moving functions around between
257 files to better group them and improving the interfaces like dropping return
258 values for functions that never fail. Then write kerneldoc for all exported
259 functions and an overview section and integrate it all into the drm book.
261 See https://dri.freedesktop.org/docs/drm/ for what's there already.
263 Contact: Daniel Vetter
265 Make panic handling work
266 ------------------------
268 This is a really varied tasks with lots of little bits and pieces:
270 * The panic path can't be tested currently, leading to constant breaking. The
271 main issue here is that panics can be triggered from hardirq contexts and
272 hence all panic related callback can run in hardirq context. It would be
273 awesome if we could test at least the fbdev helper code and driver code by
274 e.g. trigger calls through drm debugfs files. hardirq context could be
275 achieved by using an IPI to the local processor.
277 * There's a massive confusion of different panic handlers. DRM fbdev emulation
278 helpers have one, but on top of that the fbcon code itself also has one. We
279 need to make sure that they stop fighting over each another.
281 * ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
282 isn't a full solution for panic paths. We need to make sure that it only
283 returns true if there's a panic going on for real, and fix up all the
286 * The panic handler must never sleep, which also means it can't ever
287 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
288 even spinlocks (because NMI and hardirq can panic too). We need to either
289 make sure to not call such paths, or trylock everything. Really tricky.
291 * For the above locking troubles reasons it's pretty much impossible to
292 attempt a synchronous modeset from panic handlers. The only thing we could
293 try to achive is an atomic ``set_base`` of the primary plane, and hope that
294 it shows up. Everything else probably needs to be delayed to some worker or
295 something else which happens later on. Otherwise it just kills the box
296 harder, prevent the panic from going out on e.g. netconsole.
298 * There's also proposal for a simplied DRM console instead of the full-blown
299 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
300 obviously work for both console, in case we ever get kmslog merged.
302 Contact: Daniel Vetter
304 Clean up the debugfs support
305 ----------------------------
307 There's a bunch of issues with it:
309 - The drm_info_list ->show() function doesn't even bother to cast to the drm
310 structure for you. This is lazy.
312 - We probably want to have some support for debugfs files on crtc/connectors and
313 maybe other kms objects directly in core. There's even drm_print support in
314 the funcs for these objects to dump kms state, so it's all there. And then the
315 ->show() functions should obviously give you a pointer to the right object.
317 - The drm_info_list stuff is centered on drm_minor instead of drm_device. For
318 anything we want to print drm_device (or maybe drm_file) is the right thing.
320 - The drm_driver->debugfs_init hooks we have is just an artifact of the old
321 midlayered load sequence. DRM debugfs should work more like sysfs, where you
322 can create properties/files for an object anytime you want, and the core
323 takes care of publishing/unpuplishing all the files at register/unregister
324 time. Drivers shouldn't need to worry about these technicalities, and fixing
325 this (together with the drm_minor->drm_device move) would allow us to remove
328 Contact: Daniel Vetter
333 Some of these date from the very introduction of KMS in 2008 ...
335 - drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should
336 be renamed to drm_mode_config.object_idr.
338 - drm_display_mode doesn't need to be derived from drm_mode_object. That's
339 leftovers from older (never merged into upstream) KMS designs where modes
340 where set using their ID, including support to add/remove modes.
342 - Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
343 function tables in drivers, but before we can remove them we need to make sure
344 that all the users in helpers and drivers do correctly check for a NULL
347 - Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
348 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
349 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
350 historical reasons) misnamed drm_primary_helper_destroy() function.
355 Enable trinity for DRM
356 ----------------------
358 And fix up the fallout. Should be really interesting ...
360 Make KMS tests in i-g-t generic
361 -------------------------------
363 The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
364 including tons of testcases for corner-cases in the modesetting API. It would
365 be awesome if those tests (at least the ones not relying on Intel-specific GEM
366 features) could be made to run on any KMS driver.
368 Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
369 converting things over. For modeset tests we also first need a bit of
370 infrastructure to use dumb buffers for untiled buffers, to be able to run all
371 the non-i915 specific modeset tests.
373 Extend virtual test driver (VKMS)
374 ---------------------------------
376 See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
377 internship task, since it only requires a virtual machine and can be sized to
378 fit the available time.
380 Contact: Daniel Vetter
388 Tinydrm is the helper driver for really simple fb drivers. The goal is to make
389 those drivers as simple as possible, so lots of room for refactoring:
391 - backlight helpers, probably best to put them into a new drm_backlight.c.
392 This is because drivers/video is de-facto unmaintained. We could also
393 move drivers/video/backlight to drivers/gpu/backlight and take it all
394 over within drm-misc, but that's more work. Backlight helpers require a fair
395 bit of reworking and refactoring. A simple example is the enabling of a backlight.
396 Tinydrm has helpers for this. It would be good if other drivers can also use the
397 helper. However, there are various cases we need to consider i.e different
398 drivers seem to have different ways of enabling/disabling a backlight.
399 We also need to consider the backlight drivers (like gpio_backlight). The situation
400 is further complicated by the fact that the backlight is tied to fbdev
401 via fb_notifier_callback() which has complicated logic. For further details, refer
402 to the following discussion thread:
403 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA
405 - spi helpers, probably best put into spi core/helper code. Thierry said
406 the spi maintainer is fast&reactive, so shouldn't be a big issue.
408 - extract the mipi-dbi helper (well, the non-tinydrm specific parts at
409 least) into a separate helper, like we have for mipi-dsi already. Or follow
410 one of the ideas for having a shared dsi/dbi helper, abstracting away the
411 transport details more.
413 - tinydrm_gem_cma_prime_import_sg_table should probably go into the cma
414 helpers, as a _vmapped variant (since not every driver needs the vmap).
415 And tinydrm_gem_cma_free_object could the be merged into
416 drm_gem_cma_free_object().
418 - tinydrm_fb_create we could move into drm_simple_pipe, only need to add
419 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a
420 bunch of things (since it gives you a one-stop vfunc for simple drivers).
422 - Quick aside: The unregister devm stuff is kinda getting the lifetimes of
423 a drm_device wrong. Doesn't matter, since everyone else gets it wrong
426 - also rework the drm_framebuffer_funcs->dirty hook wire-up, see above.
428 Contact: Noralf Trønnes, Daniel Vetter
430 AMD DC Display Driver
431 ---------------------
433 AMD DC is the display driver for AMD devices starting with Vega. There has been
434 a bunch of progress cleaning it up but there's still plenty of work to be done.
436 See drivers/gpu/drm/amd/display/TODO for tasks.
438 Contact: Harry Wentland, Alex Deucher
443 - Our early/late pm callbacks could be removed in favour of using
444 device_link_add to model the dependency between i915 and snd_had. See
445 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html