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instead. 33Audit each individual driver, make sure it'll work with the generic 34implementation (there's lots of outdated locking leftovers in various 35implementations), and then remove it. 36 37Contact: Daniel Vetter, respective driver maintainers 38 39Level: Intermediate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 108Somewhat related is the legacy_cursor_update hack, which should be replaced with 109the new atomic_async_check/commit functionality in the helpers in drivers that 110still look at that flag. 111 112Contact: Daniel Vetter, respective driver maintainers 113 114Level: Advanced 115 116Fallout from atomic KMS 117----------------------- 118 119``drm_atomic_helper.c`` provides a batch of functions which implement legacy 120IOCTLs on top of the new atomic driver interface. Which is really nice for 121gradual conversion of drivers, but unfortunately the semantic mismatches are 122a bit too severe. So there's some follow-up work to adjust the function 123interfaces to fix these issues: 124 125* atomic needs the lock acquire context. At the moment that's passed around 126 implicitly with some horrible hacks, and it's also allocate with 127 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 128 the acquire context explicitly on stack and then also pass it down into 129 drivers explicitly so that the legacy-on-atomic functions can use them. 130 131 Except for some driver code this is done. This task should be finished by 132 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 133 134* A bunch of the vtable hooks are now in the wrong place: DRM has a split 135 between core vfunc tables (named ``drm_foo_funcs``), which are used to 136 implement the userspace ABI. And then there's the optional hooks for the 137 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 138 internal use. Some of these hooks should be move from ``_funcs`` to 139 ``_helper_funcs`` since they are not part of the core ABI. There's a 140 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 141 142Contact: Daniel Vetter 143 144Level: Intermediate 145 146Get rid of dev->struct_mutex from GEM drivers 147--------------------------------------------- 148 149``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 150everything. Nowadays in modern drivers the only bit where it's mandatory is 151serializing GEM buffer object destruction. Which unfortunately means drivers 152have to keep track of that lock and either call ``unreference`` or 153``unreference_locked`` depending upon context. 154 155Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 156and there's a GEM object ``free`` callback for any drivers which are 157entirely ``struct_mutex`` free. 158 159For drivers that need ``struct_mutex`` it should be replaced with a driver- 160private lock. The tricky part is the BO free functions, since those can't 161reliably take that lock any more. Instead state needs to be protected with 162suitable subordinate locks or some cleanup work pushed to a worker thread. For 163performance-critical drivers it might also be better to go with a more 164fine-grained per-buffer object and per-context lockings scheme. Currently only 165the ``msm`` and `i915` drivers use ``struct_mutex``. 166 167Contact: Daniel Vetter, respective driver maintainers 168 169Level: Advanced 170 171Convert logging to drm_* functions with drm_device paramater 172------------------------------------------------------------ 173 174For drivers which could have multiple instances, it is necessary to 175differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 176don't do this, drivers used dev_info/warn/err to make this differentiation. We 177now have drm_* variants of the drm print functions, so we can start to convert 178those drivers back to using drm-formatted specific log messages. 179 180Before you start this conversion please contact the relevant maintainers to make 181sure your work will be merged - not everyone agrees that the DRM dmesg macros 182are better. 183 184Contact: Sean Paul, Maintainer of the driver you plan to convert 185 186Level: Starter 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(). Also there's still open-coded version 194of the atomic suspend/resume code in older atomic modeset drivers. 195 196Contact: Maintainer of the driver you plan to convert 197 198Level: Intermediate 199 200Convert drivers to use drm_fbdev_generic_setup() 201------------------------------------------------ 202 203Most drivers can use drm_fbdev_generic_setup(). Driver have to implement 204atomic modesetting and GEM vmap support. Current generic fbdev emulation 205expects the framebuffer in system memory (or system-like memory). 206 207Contact: Maintainer of the driver you plan to convert 208 209Level: Intermediate 210 211drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 212----------------------------------------------------------------- 213 214A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 215Various hold-ups: 216 217- Need to switch over to the generic dirty tracking code using 218 drm_atomic_helper_dirtyfb first (e.g. qxl). 219 220- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 221 setup code can't be deleted. 222 223- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For 224 atomic drivers we could check for valid formats by calling 225 drm_plane_check_pixel_format() against all planes, and pass if any plane 226 supports the format. For non-atomic that's not possible since like the format 227 list for the primary plane is fake and we'd therefor reject valid formats. 228 229- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 230 version of the varios drm_gem_fb_create functions. Maybe called 231 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 232 233Contact: Daniel Vetter 234 235Level: Intermediate 236 237Clean up mmap forwarding 238------------------------ 239 240A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 241And also a lot of them forward dma-buf mmap to the gem mmap implementations. 242There's drm_gem_prime_mmap() for this now, but still needs to be rolled out. 243 244Contact: Daniel Vetter 245 246Level: Intermediate 247 248Generic fbdev defio support 249--------------------------- 250 251The defio support code in the fbdev core has some very specific requirements, 252which means drivers need to have a special framebuffer for fbdev. The main 253issue is that it uses some fields in struct page itself, which breaks shmem 254gem objects (and other things). To support defio, affected drivers require 255the use of a shadow buffer, which may add CPU and memory overhead. 256 257Possible solution would be to write our own defio mmap code in the drm fbdev 258emulation. It would need to fully wrap the existing mmap ops, forwarding 259everything after it has done the write-protect/mkwrite trickery: 260 261- In the drm_fbdev_fb_mmap helper, if we need defio, change the 262 default page prots to write-protected with something like this:: 263 264 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 265 266- Set the mkwrite and fsync callbacks with similar implementions to the core 267 fbdev defio stuff. These should all work on plain ptes, they don't actually 268 require a struct page. uff. These should all work on plain ptes, they don't 269 actually require a struct page. 270 271- Track the dirty pages in a separate structure (bitfield with one bit per page 272 should work) to avoid clobbering struct page. 273 274Might be good to also have some igt testcases for this. 275 276Contact: Daniel Vetter, Noralf Tronnes 277 278Level: Advanced 279 280idr_init_base() 281--------------- 282 283DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 284userspace IDs to internal objects, and in most places ID=0 means NULL and hence 285is never used. Switching to idr_init_base() for these would make the idr more 286efficient. 287 288Contact: Daniel Vetter 289 290Level: Starter 291 292struct drm_gem_object_funcs 293--------------------------- 294 295GEM objects can now have a function table instead of having the callbacks on the 296DRM driver struct. This is now the preferred way. Callbacks in drivers have been 297converted, except for struct drm_driver.gem_prime_mmap. 298 299Level: Intermediate 300 301Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 302--------------------------------------------------------- 303 304For cases where drivers are attempting to grab the modeset locks with a local 305acquire context. Replace the boilerplate code surrounding 306drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 307DRM_MODESET_LOCK_ALL_END() instead. 308 309This should also be done for all places where drm_modeset_lock_all() is still 310used. 311 312As a reference, take a look at the conversions already completed in drm core. 313 314Contact: Sean Paul, respective driver maintainers 315 316Level: Starter 317 318Rename CMA helpers to DMA helpers 319--------------------------------- 320 321CMA (standing for contiguous memory allocator) is really a bit an accident of 322what these were used for first, a much better name would be DMA helpers. In the 323text these should even be called coherent DMA memory helpers (so maybe CDM, but 324no one knows what that means) since underneath they just use dma_alloc_coherent. 325 326Contact: Laurent Pinchart, Daniel Vetter 327 328Level: Intermediate (mostly because it is a huge tasks without good partial 329milestones, not technically itself that challenging) 330 331connector register/unregister fixes 332----------------------------------- 333 334- For most connectors it's a no-op to call drm_connector_register/unregister 335 directly from driver code, drm_dev_register/unregister take care of this 336 already. We can remove all of them. 337 338- For dp drivers it's a bit more a mess, since we need the connector to be 339 registered when calling drm_dp_aux_register. Fix this by instead calling 340 drm_dp_aux_init, and moving the actual registering into a late_register 341 callback as recommended in the kerneldoc. 342 343Level: Intermediate 344 345Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 346--------------------------------------------------------------- 347 348The load/unload callbacks in struct &drm_driver are very much midlayers, plus 349for historical reasons they get the ordering wrong (and we can't fix that) 350between setting up the &drm_driver structure and calling drm_dev_register(). 351 352- Rework drivers to no longer use the load/unload callbacks, directly coding the 353 load/unload sequence into the driver's probe function. 354 355- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 356 callbacks for all modern drivers. 357 358Contact: Daniel Vetter 359 360Level: Intermediate 361 362Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 363--------------------------------------------------------------- 364 365Once EDID is parsed, the monitor HDMI support information is available through 366drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 367retrieve the same information, which is less efficient. 368 369Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 370drm_display_info.is_hdmi if applicable. 371 372Contact: Laurent Pinchart, respective driver maintainers 373 374Level: Intermediate 375 376Consolidate custom driver modeset properties 377-------------------------------------------- 378 379Before atomic modeset took place, many drivers where creating their own 380properties. Among other things, atomic brought the requirement that custom, 381driver specific properties should not be used. 382 383For this task, we aim to introduce core helpers or reuse the existing ones 384if available: 385 386A quick, unconfirmed, examples list. 387 388Introduce core helpers: 389- audio (amdgpu, intel, gma500, radeon) 390- brightness, contrast, etc (armada, nouveau) - overlay only (?) 391- broadcast rgb (gma500, intel) 392- colorkey (armada, nouveau, rcar) - overlay only (?) 393- dither (amdgpu, nouveau, radeon) - varies across drivers 394- underscan family (amdgpu, radeon, nouveau) 395 396Already in core: 397- colorspace (sti) 398- tv format names, enhancements (gma500, intel) 399- tv overscan, margins, etc. (gma500, intel) 400- zorder (omapdrm) - same as zpos (?) 401 402 403Contact: Emil Velikov, respective driver maintainers 404 405Level: Intermediate 406 407Plumb drm_atomic_state all over 408------------------------------- 409 410Currently various atomic functions take just a single or a handful of 411object states (eg. plane state). While that single object state can 412suffice for some simple cases, we often have to dig out additional 413object states for dealing with various dependencies between the individual 414objects or the hardware they represent. The process of digging out the 415additional states is rather non-intuitive and error prone. 416 417To fix that most functions should rather take the overall 418drm_atomic_state as one of their parameters. The other parameters 419would generally be the object(s) we mainly want to interact with. 420 421For example, instead of 422 423.. code-block:: c 424 425 int (*atomic_check)(struct drm_plane *plane, struct drm_plane_state *state); 426 427we would have something like 428 429.. code-block:: c 430 431 int (*atomic_check)(struct drm_plane *plane, struct drm_atomic_state *state); 432 433The implementation can then trivially gain access to any required object 434state(s) via drm_atomic_get_plane_state(), drm_atomic_get_new_plane_state(), 435drm_atomic_get_old_plane_state(), and their equivalents for 436other object types. 437 438Additionally many drivers currently access the object->state pointer 439directly in their commit functions. That is not going to work if we 440eg. want to allow deeper commit pipelines as those pointers could 441then point to the states corresponding to a future commit instead of 442the current commit we're trying to process. Also non-blocking commits 443execute locklessly so there are serious concerns with dereferencing 444the object->state pointers without holding the locks that protect them. 445Use of drm_atomic_get_new_plane_state(), drm_atomic_get_old_plane_state(), 446etc. avoids these problems as well since they relate to a specific 447commit via the passed in drm_atomic_state. 448 449Contact: Ville Syrjälä, Daniel Vetter 450 451Level: Intermediate 452 453 454Core refactorings 455================= 456 457Make panic handling work 458------------------------ 459 460This is a really varied tasks with lots of little bits and pieces: 461 462* The panic path can't be tested currently, leading to constant breaking. The 463 main issue here is that panics can be triggered from hardirq contexts and 464 hence all panic related callback can run in hardirq context. It would be 465 awesome if we could test at least the fbdev helper code and driver code by 466 e.g. trigger calls through drm debugfs files. hardirq context could be 467 achieved by using an IPI to the local processor. 468 469* There's a massive confusion of different panic handlers. DRM fbdev emulation 470 helpers have one, but on top of that the fbcon code itself also has one. We 471 need to make sure that they stop fighting over each another. 472 473* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 474 isn't a full solution for panic paths. We need to make sure that it only 475 returns true if there's a panic going on for real, and fix up all the 476 fallout. 477 478* The panic handler must never sleep, which also means it can't ever 479 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 480 even spinlocks (because NMI and hardirq can panic too). We need to either 481 make sure to not call such paths, or trylock everything. Really tricky. 482 483* For the above locking troubles reasons it's pretty much impossible to 484 attempt a synchronous modeset from panic handlers. The only thing we could 485 try to achive is an atomic ``set_base`` of the primary plane, and hope that 486 it shows up. Everything else probably needs to be delayed to some worker or 487 something else which happens later on. Otherwise it just kills the box 488 harder, prevent the panic from going out on e.g. netconsole. 489 490* There's also proposal for a simplied DRM console instead of the full-blown 491 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 492 obviously work for both console, in case we ever get kmslog merged. 493 494Contact: Daniel Vetter 495 496Level: Advanced 497 498Clean up the debugfs support 499---------------------------- 500 501There's a bunch of issues with it: 502 503- The drm_info_list ->show() function doesn't even bother to cast to the drm 504 structure for you. This is lazy. 505 506- We probably want to have some support for debugfs files on crtc/connectors and 507 maybe other kms objects directly in core. There's even drm_print support in 508 the funcs for these objects to dump kms state, so it's all there. And then the 509 ->show() functions should obviously give you a pointer to the right object. 510 511- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 512 anything we want to print drm_device (or maybe drm_file) is the right thing. 513 514- The drm_driver->debugfs_init hooks we have is just an artifact of the old 515 midlayered load sequence. DRM debugfs should work more like sysfs, where you 516 can create properties/files for an object anytime you want, and the core 517 takes care of publishing/unpuplishing all the files at register/unregister 518 time. Drivers shouldn't need to worry about these technicalities, and fixing 519 this (together with the drm_minor->drm_device move) would allow us to remove 520 debugfs_init. 521 522Contact: Daniel Vetter 523 524Level: Intermediate 525 526KMS cleanups 527------------ 528 529Some of these date from the very introduction of KMS in 2008 ... 530 531- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 532 function tables in drivers, but before we can remove them we need to make sure 533 that all the users in helpers and drivers do correctly check for a NULL 534 vtable. 535 536- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 537 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 538 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 539 historical reasons) misnamed drm_primary_helper_destroy() function. 540 541Level: Intermediate 542 543Better Testing 544============== 545 546Enable trinity for DRM 547---------------------- 548 549And fix up the fallout. Should be really interesting ... 550 551Level: Advanced 552 553Make KMS tests in i-g-t generic 554------------------------------- 555 556The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 557including tons of testcases for corner-cases in the modesetting API. It would 558be awesome if those tests (at least the ones not relying on Intel-specific GEM 559features) could be made to run on any KMS driver. 560 561Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 562converting things over. For modeset tests we also first need a bit of 563infrastructure to use dumb buffers for untiled buffers, to be able to run all 564the non-i915 specific modeset tests. 565 566Level: Advanced 567 568Extend virtual test driver (VKMS) 569--------------------------------- 570 571See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 572internship task, since it only requires a virtual machine and can be sized to 573fit the available time. 574 575Contact: Daniel Vetter 576 577Level: See details 578 579Backlight Refactoring 580--------------------- 581 582Backlight drivers have a triple enable/disable state, which is a bit overkill. 583Plan to fix this: 584 5851. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 586 has started already. 5872. In all, only look at one of the three status bits set by the above helpers. 5883. Remove the other two status bits. 589 590Contact: Daniel Vetter 591 592Level: Intermediate 593 594Driver Specific 595=============== 596 597AMD DC Display Driver 598--------------------- 599 600AMD DC is the display driver for AMD devices starting with Vega. There has been 601a bunch of progress cleaning it up but there's still plenty of work to be done. 602 603See drivers/gpu/drm/amd/display/TODO for tasks. 604 605Contact: Harry Wentland, Alex Deucher 606 607Bootsplash 608========== 609 610There is support in place now for writing internal DRM clients making it 611possible to pick up the bootsplash work that was rejected because it was written 612for fbdev. 613 614- [v6,8/8] drm/client: Hack: Add bootsplash example 615 https://patchwork.freedesktop.org/patch/306579/ 616 617- [RFC PATCH v2 00/13] Kernel based bootsplash 618 https://lkml.org/lkml/2017/12/13/764 619 620Contact: Sam Ravnborg 621 622Level: Advanced 623 624Outside DRM 625=========== 626 627Convert fbdev drivers to DRM 628---------------------------- 629 630There are plenty of fbdev drivers for older hardware. Some hwardware has 631become obsolete, but some still provides good(-enough) framebuffers. The 632drivers that are still useful should be converted to DRM and afterwards 633removed from fbdev. 634 635Very simple fbdev drivers can best be converted by starting with a new 636DRM driver. Simple KMS helpers and SHMEM should be able to handle any 637existing hardware. The new driver's call-back functions are filled from 638existing fbdev code. 639 640More complex fbdev drivers can be refactored step-by-step into a DRM 641driver with the help of the DRM fbconv helpers. [1] These helpers provide 642the transition layer between the DRM core infrastructure and the fbdev 643driver interface. Create a new DRM driver on top of the fbconv helpers, 644copy over the fbdev driver, and hook it up to the DRM code. Examples for 645several fbdev drivers are available at [1] and a tutorial of this process 646available at [2]. The result is a primitive DRM driver that can run X11 647and Weston. 648 649 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 650 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 651 652Contact: Thomas Zimmermann <tzimmermann@suse.de> 653 654Level: Advanced 655