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 13De-midlayer drivers 14------------------- 15 16With the recent ``drm_bus`` cleanup patches for 3.17 it is no longer required 17to 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`` 19and ``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 21the new two-stage ``drm_device`` setup/teardown. 22 23Once all existing drivers are converted we can also remove those bus support 24files for USB and platform devices. 25 26All you need is a GPU for a non-converted driver (currently almost all of 27them, but also all the virtual ones used by KVM, so everyone qualifies). 28 29Contact: Daniel Vetter, Thierry Reding, respective driver maintainers 30 31Switch from reference/unreference to get/put 32-------------------------------------------- 33 34For some reason DRM core uses ``reference``/``unreference`` suffixes for 35refcounting functions, but kernel uses ``get``/``put`` (e.g. 36``kref_get``/``put()``). It would be good to switch over for consistency, and 37it'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 44This way drivers/patches in the progress of getting merged won't break. 45 46Contact: Daniel Vetter 47 48Convert existing KMS drivers to atomic modesetting 49-------------------------------------------------- 50 513.19 has the atomic modeset interfaces and helpers, so drivers can now be 52converted over. Modern compositors like Wayland or Surfaceflinger on Android 53really want an atomic modeset interface, so this is all about the bright 54future. 55 56There is a conversion guide for atomic and all you need is a GPU for a 57non-converted driver (again virtual HW drivers for KVM are still all 58suitable). 59 60As part of this drivers also need to convert to universal plane (which means 61exposing primary & cursor as proper plane objects). But that's much easier to 62do by directly using the new atomic helper driver callbacks. 63 64Contact: Daniel Vetter, respective driver maintainers 65 66Clean up the clipped coordination confusion around planes 67--------------------------------------------------------- 68 69We have a helper to get this right with drm_plane_helper_check_update(), but 70it's not consistently used. This should be fixed, preferrably in the atomic 71helpers (and drivers then moved over to clipped coordinates). Probably the 72helper should also be moved from drm_plane_helper.c to the atomic helpers, to 73avoid confusion - the other helpers in that file are all deprecated legacy 74helpers. 75 76Contact: Ville Syrjälä, Daniel Vetter, driver maintainers 77 78Convert early atomic drivers to async commit helpers 79---------------------------------------------------- 80 81For the first year the atomic modeset helpers didn't support asynchronous / 82nonblocking commits, and every driver had to hand-roll them. This is fixed 83now, but there's still a pile of existing drivers that easily could be 84converted over to the new infrastructure. 85 86One issue with the helpers is that they require that drivers handle completion 87events for atomic commits correctly. But fixing these bugs is good anyway. 88 89Contact: Daniel Vetter, respective driver maintainers 90 91Better manual-upload support for atomic 92--------------------------------------- 93 94This would be especially useful for tinydrm: 95 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(). 99 100- 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. 103 104- 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. 112 113Contact: Noralf Trønnes, Daniel Vetter 114 115Fallout from atomic KMS 116----------------------- 117 118``drm_atomic_helper.c`` provides a batch of functions which implement legacy 119IOCTLs on top of the new atomic driver interface. Which is really nice for 120gradual conversion of drivers, but unfortunately the semantic mismatches are 121a bit too severe. So there's some follow-up work to adjust the function 122interfaces to fix these issues: 123 124* 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. 129 130 Except for some driver code this is done. 131 132* A bunch of the vtable hooks are now in the wrong place: DRM has a split 133 between core vfunc tables (named ``drm_foo_funcs``), which are used to 134 implement the userspace ABI. And then there's the optional hooks for the 135 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 136 internal use. Some of these hooks should be move from ``_funcs`` to 137 ``_helper_funcs`` since they are not part of the core ABI. There's a 138 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 139 140* There's a new helper ``drm_atomic_helper_best_encoder()`` which could be 141 used by all atomic drivers which don't select the encoder for a given 142 connector at runtime. That's almost all of them, and would allow us to get 143 rid of a lot of ``best_encoder`` boilerplate in drivers. 144 145 This was almost done, but new drivers added a few more cases again. 146 147Contact: Daniel Vetter 148 149Get rid of dev->struct_mutex from GEM drivers 150--------------------------------------------- 151 152``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 153everything. Nowadays in modern drivers the only bit where it's mandatory is 154serializing GEM buffer object destruction. Which unfortunately means drivers 155have to keep track of that lock and either call ``unreference`` or 156``unreference_locked`` depending upon context. 157 158Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 159and there's a ``gem_free_object_unlocked`` callback for any drivers which are 160entirely ``struct_mutex`` free. 161 162For drivers that need ``struct_mutex`` it should be replaced with a driver- 163private lock. The tricky part is the BO free functions, since those can't 164reliably take that lock any more. Instead state needs to be protected with 165suitable subordinate locks or some cleanup work pushed to a worker thread. For 166performance-critical drivers it might also be better to go with a more 167fine-grained per-buffer object and per-context lockings scheme. Currently the 168following drivers still use ``struct_mutex``: ``msm``, ``omapdrm`` and 169``udl``. 170 171Contact: Daniel Vetter, respective driver maintainers 172 173Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent 174---------------------------------------------------------------------------- 175 176For drivers which could have multiple instances, it is necessary to 177differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 178don't do this, drivers used dev_info/warn/err to make this differentiation. We 179now have DRM_DEV_* variants of the drm print macros, so we can start to convert 180those drivers back to using drm-formwatted specific log messages. 181 182Before you start this conversion please contact the relevant maintainers to make 183sure your work will be merged - not everyone agrees that the DRM dmesg macros 184are better. 185 186Contact: Sean Paul, Maintainer of the driver you plan to convert 187 188Convert drivers to use simple modeset suspend/resume 189---------------------------------------------------- 190 191Most drivers (except i915 and nouveau) that use 192drm_atomic_helper_suspend/resume() can probably be converted to use 193drm_mode_config_helper_suspend/resume(). 194 195Contact: Maintainer of the driver you plan to convert 196 197Convert drivers to use drm_fb_helper_fbdev_setup/teardown() 198----------------------------------------------------------- 199 200Most drivers can use drm_fb_helper_fbdev_setup() except maybe: 201 202- amdgpu which has special logic to decide whether to call 203 drm_helper_disable_unused_functions() 204 205- armada which isn't atomic and doesn't call 206 drm_helper_disable_unused_functions() 207 208- i915 which calls drm_fb_helper_initial_config() in a worker 209 210Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can 211probably use drm_fb_helper_fbdev_teardown(). 212 213Contact: Maintainer of the driver you plan to convert 214 215Core refactorings 216================= 217 218Clean up the DRM header mess 219---------------------------- 220 221Currently the DRM subsystem has only one global header, ``drmP.h``. This is 222used both for functions exported to helper libraries and drivers and functions 223only used internally in the ``drm.ko`` module. The goal would be to move all 224header declarations not needed outside of ``drm.ko`` into 225``drivers/gpu/drm/drm_*_internal.h`` header files. ``EXPORT_SYMBOL`` also 226needs to be dropped for these functions. 227 228This would nicely tie in with the below task to create kerneldoc after the API 229is cleaned up. Or with the "hide legacy cruft better" task. 230 231Note that this is well in progress, but ``drmP.h`` is still huge. The updated 232plan is to switch to per-file driver API headers, which will also structure 233the kerneldoc better. This should also allow more fine-grained ``#include`` 234directives. 235 236In the end no .c file should need to include ``drmP.h`` anymore. 237 238Contact: Daniel Vetter 239 240Add missing kerneldoc for exported functions 241-------------------------------------------- 242 243The DRM reference documentation is still lacking kerneldoc in a few areas. The 244task would be to clean up interfaces like moving functions around between 245files to better group them and improving the interfaces like dropping return 246values for functions that never fail. Then write kerneldoc for all exported 247functions and an overview section and integrate it all into the drm book. 248 249See https://dri.freedesktop.org/docs/drm/ for what's there already. 250 251Contact: Daniel Vetter 252 253Hide legacy cruft better 254------------------------ 255 256Way back DRM supported only drivers which shadow-attached to PCI devices with 257userspace or fbdev drivers setting up outputs. Modern DRM drivers take charge 258of the entire device, you can spot them with the DRIVER_MODESET flag. 259 260Unfortunately there's still large piles of legacy code around which needs to 261be hidden so that driver writers don't accidentally end up using it. And to 262prevent security issues in those legacy IOCTLs from being exploited on modern 263drivers. This has multiple possible subtasks: 264 265* Extract support code for legacy features into a ``drm-legacy.ko`` kernel 266 module and compile it only when one of the legacy drivers is enabled. 267 268This is mostly done, the only thing left is to split up ``drm_irq.c`` into 269legacy cruft and the parts needed by modern KMS drivers. 270 271Contact: Daniel Vetter 272 273Make panic handling work 274------------------------ 275 276This is a really varied tasks with lots of little bits and pieces: 277 278* The panic path can't be tested currently, leading to constant breaking. The 279 main issue here is that panics can be triggered from hardirq contexts and 280 hence all panic related callback can run in hardirq context. It would be 281 awesome if we could test at least the fbdev helper code and driver code by 282 e.g. trigger calls through drm debugfs files. hardirq context could be 283 achieved by using an IPI to the local processor. 284 285* There's a massive confusion of different panic handlers. DRM fbdev emulation 286 helpers have one, but on top of that the fbcon code itself also has one. We 287 need to make sure that they stop fighting over each another. 288 289* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 290 isn't a full solution for panic paths. We need to make sure that it only 291 returns true if there's a panic going on for real, and fix up all the 292 fallout. 293 294* The panic handler must never sleep, which also means it can't ever 295 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 296 even spinlocks (because NMI and hardirq can panic too). We need to either 297 make sure to not call such paths, or trylock everything. Really tricky. 298 299* For the above locking troubles reasons it's pretty much impossible to 300 attempt a synchronous modeset from panic handlers. The only thing we could 301 try to achive is an atomic ``set_base`` of the primary plane, and hope that 302 it shows up. Everything else probably needs to be delayed to some worker or 303 something else which happens later on. Otherwise it just kills the box 304 harder, prevent the panic from going out on e.g. netconsole. 305 306* There's also proposal for a simplied DRM console instead of the full-blown 307 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 308 obviously work for both console, in case we ever get kmslog merged. 309 310Contact: Daniel Vetter 311 312Clean up the debugfs support 313---------------------------- 314 315There's a bunch of issues with it: 316 317- The drm_info_list ->show() function doesn't even bother to cast to the drm 318 structure for you. This is lazy. 319 320- We probably want to have some support for debugfs files on crtc/connectors and 321 maybe other kms objects directly in core. There's even drm_print support in 322 the funcs for these objects to dump kms state, so it's all there. And then the 323 ->show() functions should obviously give you a pointer to the right object. 324 325- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 326 anything we want to print drm_device (or maybe drm_file) is the right thing. 327 328- The drm_driver->debugfs_init hooks we have is just an artifact of the old 329 midlayered load sequence. DRM debugfs should work more like sysfs, where you 330 can create properties/files for an object anytime you want, and the core 331 takes care of publishing/unpuplishing all the files at register/unregister 332 time. Drivers shouldn't need to worry about these technicalities, and fixing 333 this (together with the drm_minor->drm_device move) would allow us to remove 334 debugfs_init. 335 336Contact: Daniel Vetter 337 338KMS cleanups 339------------ 340 341Some of these date from the very introduction of KMS in 2008 ... 342 343- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should 344 be renamed to drm_mode_config.object_idr. 345 346- drm_display_mode doesn't need to be derived from drm_mode_object. That's 347 leftovers from older (never merged into upstream) KMS designs where modes 348 where set using their ID, including support to add/remove modes. 349 350Better Testing 351============== 352 353Enable trinity for DRM 354---------------------- 355 356And fix up the fallout. Should be really interesting ... 357 358Make KMS tests in i-g-t generic 359------------------------------- 360 361The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 362including tons of testcases for corner-cases in the modesetting API. It would 363be awesome if those tests (at least the ones not relying on Intel-specific GEM 364features) could be made to run on any KMS driver. 365 366Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 367converting things over. For modeset tests we also first need a bit of 368infrastructure to use dumb buffers for untiled buffers, to be able to run all 369the non-i915 specific modeset tests. 370 371Contact: Daniel Vetter 372 373Create a virtual KMS driver for testing (vkms) 374---------------------------------------------- 375 376With all the latest helpers it should be fairly simple to create a virtual KMS 377driver useful for testing, or for running X or similar on headless machines 378(to be able to still use the GPU). This would be similar to vgem, but aimed at 379the modeset side. 380 381Once the basics are there there's tons of possibilities to extend it. 382 383Contact: Daniel Vetter 384 385Driver Specific 386=============== 387 388tinydrm 389------- 390 391Tinydrm is the helper driver for really simple fb drivers. The goal is to make 392those drivers as simple as possible, so lots of room for refactoring: 393 394- backlight helpers, probably best to put them into a new drm_backlight.c. 395 This is because drivers/video is de-facto unmaintained. We could also 396 move drivers/video/backlight to drivers/gpu/backlight and take it all 397 over within drm-misc, but that's more work. Backlight helpers require a fair 398 bit of reworking and refactoring. A simple example is the enabling of a backlight. 399 Tinydrm has helpers for this. It would be good if other drivers can also use the 400 helper. However, there are various cases we need to consider i.e different 401 drivers seem to have different ways of enabling/disabling a backlight. 402 We also need to consider the backlight drivers (like gpio_backlight). The situation 403 is further complicated by the fact that the backlight is tied to fbdev 404 via fb_notifier_callback() which has complicated logic. For further details, refer 405 to the following discussion thread: 406 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 407 408- spi helpers, probably best put into spi core/helper code. Thierry said 409 the spi maintainer is fast&reactive, so shouldn't be a big issue. 410 411- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 412 least) into a separate helper, like we have for mipi-dsi already. Or follow 413 one of the ideas for having a shared dsi/dbi helper, abstracting away the 414 transport details more. 415 416- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma 417 helpers, as a _vmapped variant (since not every driver needs the vmap). 418 And tinydrm_gem_cma_free_object could the be merged into 419 drm_gem_cma_free_object(). 420 421- tinydrm_fb_create we could move into drm_simple_pipe, only need to add 422 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a 423 bunch of things (since it gives you a one-stop vfunc for simple drivers). 424 425- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 426 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 427 too :-) 428 429- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. 430 431Contact: Noralf Trønnes, Daniel Vetter 432 433AMD DC Display Driver 434--------------------- 435 436AMD DC is the display driver for AMD devices starting with Vega. There has been 437a bunch of progress cleaning it up but there's still plenty of work to be done. 438 439See drivers/gpu/drm/amd/display/TODO for tasks. 440 441Contact: Harry Wentland, Alex Deucher 442 443Outside DRM 444=========== 445