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 Implement deferred fbdev setup in the helper
79 --------------------------------------------
81 Many (especially embedded drivers) want to delay fbdev setup until there's a
82 real screen plugged in. This is to avoid the dreaded fallback to the low-res
83 fbdev default. Many drivers have a hacked-up (and often broken) version of this,
84 better to do it once in the shared helpers. Thierry has a patch series, but that
85 one needs to be rebased and final polish applied.
87 Contact: Thierry Reding, Daniel Vetter, driver maintainers
89 Convert early atomic drivers to async commit helpers
90 ----------------------------------------------------
92 For the first year the atomic modeset helpers didn't support asynchronous /
93 nonblocking commits, and every driver had to hand-roll them. This is fixed
94 now, but there's still a pile of existing drivers that easily could be
95 converted over to the new infrastructure.
97 One issue with the helpers is that they require that drivers handle completion
98 events for atomic commits correctly. But fixing these bugs is good anyway.
100 Contact: Daniel Vetter, respective driver maintainers
102 Better manual-upload support for atomic
103 ---------------------------------------
105 This would be especially useful for tinydrm:
107 - Add a struct drm_rect dirty_clip to drm_crtc_state. When duplicating the
108 crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in
109 __drm_atomic_helper_crtc_duplicate_state().
111 - Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_
112 prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this
113 is a function useful to implement the fb->dirty function.
115 - Create a new drm_fb_dirty function which does essentially what e.g.
116 mipi_dbi_fb_dirty does. You can use e.g. drm_atomic_helper_update_plane as the
117 template. But instead of doing a simple full-screen plane update, this new
118 helper also sets crtc_state->dirty_clip to the right coordinates. And of
119 course it needs to check whether the fb is actually active (and maybe where),
120 so there's some book-keeping involved. There's also some good fun involved in
121 scaling things appropriately. For that case we might simply give up and
122 declare the entire area covered by the plane as dirty.
124 Contact: Noralf Trønnes, Daniel Vetter
126 Fallout from atomic KMS
127 -----------------------
129 ``drm_atomic_helper.c`` provides a batch of functions which implement legacy
130 IOCTLs on top of the new atomic driver interface. Which is really nice for
131 gradual conversion of drivers, but unfortunately the semantic mismatches are
132 a bit too severe. So there's some follow-up work to adjust the function
133 interfaces to fix these issues:
135 * atomic needs the lock acquire context. At the moment that's passed around
136 implicitly with some horrible hacks, and it's also allocate with
137 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
138 the acquire context explicitly on stack and then also pass it down into
139 drivers explicitly so that the legacy-on-atomic functions can use them.
141 * A bunch of the vtable hooks are now in the wrong place: DRM has a split
142 between core vfunc tables (named ``drm_foo_funcs``), which are used to
143 implement the userspace ABI. And then there's the optional hooks for the
144 helper libraries (name ``drm_foo_helper_funcs``), which are purely for
145 internal use. Some of these hooks should be move from ``_funcs`` to
146 ``_helper_funcs`` since they are not part of the core ABI. There's a
147 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.
149 * There's a new helper ``drm_atomic_helper_best_encoder()`` which could be
150 used by all atomic drivers which don't select the encoder for a given
151 connector at runtime. That's almost all of them, and would allow us to get
152 rid of a lot of ``best_encoder`` boilerplate in drivers.
154 Contact: Daniel Vetter
156 Get rid of dev->struct_mutex from GEM drivers
157 ---------------------------------------------
159 ``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
160 everything. Nowadays in modern drivers the only bit where it's mandatory is
161 serializing GEM buffer object destruction. Which unfortunately means drivers
162 have to keep track of that lock and either call ``unreference`` or
163 ``unreference_locked`` depending upon context.
165 Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
166 and there's a ``gem_free_object_unlocked`` callback for any drivers which are
167 entirely ``struct_mutex`` free.
169 For drivers that need ``struct_mutex`` it should be replaced with a driver-
170 private lock. The tricky part is the BO free functions, since those can't
171 reliably take that lock any more. Instead state needs to be protected with
172 suitable subordinate locks or some cleanup work pushed to a worker thread. For
173 performance-critical drivers it might also be better to go with a more
174 fine-grained per-buffer object and per-context lockings scheme. Currently the
175 following drivers still use ``struct_mutex``: ``msm``, ``omapdrm`` and
178 Contact: Daniel Vetter, respective driver maintainers
183 Use new IDR deletion interface to clean up drm_gem_handle_delete()
184 ------------------------------------------------------------------
186 See the "This is gross" comment -- apparently the IDR system now can return an
187 error code instead of oopsing.
189 Clean up the DRM header mess
190 ----------------------------
192 Currently the DRM subsystem has only one global header, ``drmP.h``. This is
193 used both for functions exported to helper libraries and drivers and functions
194 only used internally in the ``drm.ko`` module. The goal would be to move all
195 header declarations not needed outside of ``drm.ko`` into
196 ``drivers/gpu/drm/drm_*_internal.h`` header files. ``EXPORT_SYMBOL`` also
197 needs to be dropped for these functions.
199 This would nicely tie in with the below task to create kerneldoc after the API
200 is cleaned up. Or with the "hide legacy cruft better" task.
202 Note that this is well in progress, but ``drmP.h`` is still huge. The updated
203 plan is to switch to per-file driver API headers, which will also structure
204 the kerneldoc better. This should also allow more fine-grained ``#include``
207 In the end no .c file should need to include ``drmP.h`` anymore.
209 Contact: Daniel Vetter
211 Add missing kerneldoc for exported functions
212 --------------------------------------------
214 The DRM reference documentation is still lacking kerneldoc in a few areas. The
215 task would be to clean up interfaces like moving functions around between
216 files to better group them and improving the interfaces like dropping return
217 values for functions that never fail. Then write kerneldoc for all exported
218 functions and an overview section and integrate it all into the drm book.
220 See https://dri.freedesktop.org/docs/drm/ for what's there already.
222 Contact: Daniel Vetter
224 Hide legacy cruft better
225 ------------------------
227 Way back DRM supported only drivers which shadow-attached to PCI devices with
228 userspace or fbdev drivers setting up outputs. Modern DRM drivers take charge
229 of the entire device, you can spot them with the DRIVER_MODESET flag.
231 Unfortunately there's still large piles of legacy code around which needs to
232 be hidden so that driver writers don't accidentally end up using it. And to
233 prevent security issues in those legacy IOCTLs from being exploited on modern
234 drivers. This has multiple possible subtasks:
236 * Extract support code for legacy features into a ``drm-legacy.ko`` kernel
237 module and compile it only when one of the legacy drivers is enabled.
239 This is mostly done, the only thing left is to split up ``drm_irq.c`` into
240 legacy cruft and the parts needed by modern KMS drivers.
242 Contact: Daniel Vetter
244 Make panic handling work
245 ------------------------
247 This is a really varied tasks with lots of little bits and pieces:
249 * The panic path can't be tested currently, leading to constant breaking. The
250 main issue here is that panics can be triggered from hardirq contexts and
251 hence all panic related callback can run in hardirq context. It would be
252 awesome if we could test at least the fbdev helper code and driver code by
253 e.g. trigger calls through drm debugfs files. hardirq context could be
254 achieved by using an IPI to the local processor.
256 * There's a massive confusion of different panic handlers. DRM fbdev emulation
257 helpers have one, but on top of that the fbcon code itself also has one. We
258 need to make sure that they stop fighting over each another.
260 * ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
261 isn't a full solution for panic paths. We need to make sure that it only
262 returns true if there's a panic going on for real, and fix up all the
265 * The panic handler must never sleep, which also means it can't ever
266 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
267 even spinlocks (because NMI and hardirq can panic too). We need to either
268 make sure to not call such paths, or trylock everything. Really tricky.
270 * For the above locking troubles reasons it's pretty much impossible to
271 attempt a synchronous modeset from panic handlers. The only thing we could
272 try to achive is an atomic ``set_base`` of the primary plane, and hope that
273 it shows up. Everything else probably needs to be delayed to some worker or
274 something else which happens later on. Otherwise it just kills the box
275 harder, prevent the panic from going out on e.g. netconsole.
277 * There's also proposal for a simplied DRM console instead of the full-blown
278 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
279 obviously work for both console, in case we ever get kmslog merged.
281 Contact: Daniel Vetter
283 Clean up the debugfs support
284 ----------------------------
286 There's a bunch of issues with it:
288 - The drm_info_list ->show() function doesn't even bother to cast to the drm
289 structure for you. This is lazy.
291 - We probably want to have some support for debugfs files on crtc/connectors and
292 maybe other kms objects directly in core. There's even drm_print support in
293 the funcs for these objects to dump kms state, so it's all there. And then the
294 ->show() functions should obviously give you a pointer to the right object.
296 - The drm_info_list stuff is centered on drm_minor instead of drm_device. For
297 anything we want to print drm_device (or maybe drm_file) is the right thing.
299 - The drm_driver->debugfs_init hooks we have is just an artifact of the old
300 midlayered load sequence. DRM debugfs should work more like sysfs, where you
301 can create properties/files for an object anytime you want, and the core
302 takes care of publishing/unpuplishing all the files at register/unregister
303 time. Drivers shouldn't need to worry about these technicalities, and fixing
304 this (together with the drm_minor->drm_device move) would allow us to remove
307 Contact: Daniel Vetter
312 Enable trinity for DRM
313 ----------------------
315 And fix up the fallout. Should be really interesting ...
317 Make KMS tests in i-g-t generic
318 -------------------------------
320 The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
321 including tons of testcases for corner-cases in the modesetting API. It would
322 be awesome if those tests (at least the ones not relying on Intel-specific GEM
323 features) could be made to run on any KMS driver.
325 Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
326 converting things over. For modeset tests we also first need a bit of
327 infrastructure to use dumb buffers for untiled buffers, to be able to run all
328 the non-i915 specific modeset tests.
330 Contact: Daniel Vetter
332 Create a virtual KMS driver for testing (vkms)
333 ----------------------------------------------
335 With all the latest helpers it should be fairly simple to create a virtual KMS
336 driver useful for testing, or for running X or similar on headless machines
337 (to be able to still use the GPU). This would be similar to vgem, but aimed at
340 Once the basics are there there's tons of possibilities to extend it.
342 Contact: Daniel Vetter
350 Tinydrm is the helper driver for really simple fb drivers. The goal is to make
351 those drivers as simple as possible, so lots of room for refactoring:
353 - backlight helpers, probably best to put them into a new drm_backlight.c.
354 This is because drivers/video is de-facto unmaintained. We could also
355 move drivers/video/backlight to drivers/gpu/backlight and take it all
356 over within drm-misc, but that's more work.
358 - spi helpers, probably best put into spi core/helper code. Thierry said
359 the spi maintainer is fast&reactive, so shouldn't be a big issue.
361 - extract the mipi-dbi helper (well, the non-tinydrm specific parts at
362 least) into a separate helper, like we have for mipi-dsi already. Or follow
363 one of the ideas for having a shared dsi/dbi helper, abstracting away the
364 transport details more.
366 - tinydrm_lastclose could be drm_fb_helper_lastclose. Only thing we need
367 for that is to store the drm_fb_helper pointer somewhere in
368 drm_device->mode_config. And then we could roll that out to all the
371 - tinydrm_gem_cma_prime_import_sg_table should probably go into the cma
372 helpers, as a _vmapped variant (since not every driver needs the vmap).
373 And tinydrm_gem_cma_free_object could the be merged into
374 drm_gem_cma_free_object().
376 - tinydrm_fb_create we could move into drm_simple_pipe, only need to add
377 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a
378 bunch of things (since it gives you a one-stop vfunc for simple drivers).
380 - Quick aside: The unregister devm stuff is kinda getting the lifetimes of
381 a drm_device wrong. Doesn't matter, since everyone else gets it wrong
384 - With the fbdev pointer in dev->mode_config we could also make
385 suspend/resume helpers entirely generic, at least if we add a
386 dev->mode_config.suspend_state. We could even provide a generic pm_ops
387 structure with those.
389 - also rework the drm_framebuffer_funcs->dirty hook wire-up, see above.
391 Contact: Noralf Trønnes, Daniel Vetter
projects / linux-2.6-microblaze.git / blob