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0e70dad0 TR |
1 | .. _todo: |
2 | ||
3 | ========= | |
4 | TODO list | |
5 | ========= | |
6 | ||
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. | |
9 | ||
10 | Subsystem-wide refactorings | |
11 | =========================== | |
12 | ||
13 | De-midlayer drivers | |
14 | ------------------- | |
15 | ||
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`` | |
085c6c09 | 19 | and ``drm_pci.c``. The goal is to get rid of the driver's ``->load`` / |
0e70dad0 TR |
20 | ``->unload`` callbacks and open-code the load/unload sequence properly, using |
21 | the new two-stage ``drm_device`` setup/teardown. | |
22 | ||
23 | Once all existing drivers are converted we can also remove those bus support | |
24 | files for USB and platform devices. | |
25 | ||
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). | |
28 | ||
29 | Contact: Daniel Vetter, Thierry Reding, respective driver maintainers | |
30 | ||
31 | Switch from reference/unreference to get/put | |
32 | -------------------------------------------- | |
33 | ||
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: | |
38 | ||
39 | * Create new ``get``/``put`` functions, define the old names as compatibility | |
40 | wrappers | |
41 | * Switch over each file/driver using a cocci-generated spatch. | |
42 | * Once all users of the old names are gone, remove them. | |
43 | ||
44 | This way drivers/patches in the progress of getting merged won't break. | |
45 | ||
46 | Contact: Daniel Vetter | |
47 | ||
48 | Convert existing KMS drivers to atomic modesetting | |
49 | -------------------------------------------------- | |
50 | ||
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 | |
54 | future. | |
55 | ||
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 | |
58 | suitable). | |
59 | ||
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. | |
63 | ||
64 | Contact: Daniel Vetter, respective driver maintainers | |
1a80cc1c DV |
65 | |
66 | Clean up the clipped coordination confusion around planes | |
67 | --------------------------------------------------------- | |
68 | ||
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 | |
74 | helpers. | |
75 | ||
76 | Contact: Ville Syrjälä, Daniel Vetter, driver maintainers | |
4e8be453 DV |
77 | |
78 | Implement deferred fbdev setup in the helper | |
79 | -------------------------------------------- | |
80 | ||
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. | |
86 | ||
87 | Contact: Thierry Reding, Daniel Vetter, driver maintainers | |
0e70dad0 TR |
88 | |
89 | Convert early atomic drivers to async commit helpers | |
90 | ---------------------------------------------------- | |
91 | ||
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. | |
96 | ||
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. | |
99 | ||
100 | Contact: Daniel Vetter, respective driver maintainers | |
101 | ||
f217f554 DV |
102 | Better manual-upload support for atomic |
103 | --------------------------------------- | |
104 | ||
105 | This would be especially useful for tinydrm: | |
106 | ||
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(). | |
110 | ||
0cac6ac1 TR |
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 | |
f217f554 DV |
113 | is a function useful to implement the fb->dirty function. |
114 | ||
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. | |
123 | ||
124 | Contact: Noralf Trønnes, Daniel Vetter | |
125 | ||
0e70dad0 TR |
126 | Fallout from atomic KMS |
127 | ----------------------- | |
128 | ||
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: | |
134 | ||
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. | |
140 | ||
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``. | |
148 | ||
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. | |
153 | ||
154 | Contact: Daniel Vetter | |
155 | ||
156 | Get rid of dev->struct_mutex from GEM drivers | |
157 | --------------------------------------------- | |
158 | ||
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. | |
164 | ||
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. | |
168 | ||
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 | |
176 | ``udl``. | |
177 | ||
085c6c09 | 178 | Contact: Daniel Vetter, respective driver maintainers |
0e70dad0 TR |
179 | |
180 | Core refactorings | |
181 | ================= | |
182 | ||
183 | Use new IDR deletion interface to clean up drm_gem_handle_delete() | |
184 | ------------------------------------------------------------------ | |
185 | ||
186 | See the "This is gross" comment -- apparently the IDR system now can return an | |
187 | error code instead of oopsing. | |
188 | ||
189 | Clean up the DRM header mess | |
190 | ---------------------------- | |
191 | ||
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. | |
198 | ||
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. | |
201 | ||
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`` | |
205 | directives. | |
206 | ||
085c6c09 DV |
207 | In the end no .c file should need to include ``drmP.h`` anymore. |
208 | ||
0e70dad0 TR |
209 | Contact: Daniel Vetter |
210 | ||
211 | Add missing kerneldoc for exported functions | |
212 | -------------------------------------------- | |
213 | ||
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 | |
ff41c419 | 218 | functions and an overview section and integrate it all into the drm book. |
0e70dad0 TR |
219 | |
220 | See https://dri.freedesktop.org/docs/drm/ for what's there already. | |
221 | ||
222 | Contact: Daniel Vetter | |
223 | ||
224 | Hide legacy cruft better | |
225 | ------------------------ | |
226 | ||
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. | |
230 | ||
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: | |
235 | ||
0e70dad0 TR |
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. | |
0e70dad0 TR |
238 | |
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. | |
241 | ||
242 | Contact: Daniel Vetter | |
243 | ||
244 | Make panic handling work | |
245 | ------------------------ | |
246 | ||
247 | This is a really varied tasks with lots of little bits and pieces: | |
248 | ||
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. | |
255 | ||
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. | |
259 | ||
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 | |
263 | fallout. | |
264 | ||
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. | |
269 | ||
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. | |
276 | ||
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. | |
280 | ||
281 | Contact: Daniel Vetter | |
282 | ||
0cad7f71 DV |
283 | Clean up the debugfs support |
284 | ---------------------------- | |
285 | ||
286 | There's a bunch of issues with it: | |
287 | ||
288 | - The drm_info_list ->show() function doesn't even bother to cast to the drm | |
289 | structure for you. This is lazy. | |
290 | ||
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. | |
295 | ||
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. | |
298 | ||
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 | |
305 | debugfs_init. | |
306 | ||
307 | Contact: Daniel Vetter | |
308 | ||
0e70dad0 TR |
309 | Better Testing |
310 | ============== | |
311 | ||
312 | Enable trinity for DRM | |
313 | ---------------------- | |
314 | ||
315 | And fix up the fallout. Should be really interesting ... | |
316 | ||
317 | Make KMS tests in i-g-t generic | |
318 | ------------------------------- | |
319 | ||
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. | |
324 | ||
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. | |
329 | ||
330 | Contact: Daniel Vetter | |
331 | ||
332 | Create a virtual KMS driver for testing (vkms) | |
333 | ---------------------------------------------- | |
334 | ||
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 | |
338 | the modeset side. | |
339 | ||
340 | Once the basics are there there's tons of possibilities to extend it. | |
341 | ||
342 | Contact: Daniel Vetter | |
343 | ||
344 | Driver Specific | |
345 | =============== | |
346 | ||
f217f554 DV |
347 | tinydrm |
348 | ------- | |
349 | ||
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: | |
352 | ||
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. | |
357 | ||
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. | |
360 | ||
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. | |
365 | ||
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 | |
369 | drivers. | |
370 | ||
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(). | |
375 | ||
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). | |
379 | ||
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 | |
382 | too :-) | |
383 | ||
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. | |
388 | ||
389 | - also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. | |
390 | ||
391 | Contact: Noralf Trønnes, Daniel Vetter | |
392 | ||
0e70dad0 TR |
393 | Outside DRM |
394 | =========== |