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 26Expert: Only attempt these if you've successfully completed some tricky 27refactorings already and are an expert in the specific area 28 29Subsystem-wide refactorings 30=========================== 31 32Remove custom dumb_map_offset implementations 33--------------------------------------------- 34 35All GEM based drivers should be using drm_gem_create_mmap_offset() instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Level: Intermediate 43 44Convert existing KMS drivers to atomic modesetting 45-------------------------------------------------- 46 473.19 has the atomic modeset interfaces and helpers, so drivers can now be 48converted over. Modern compositors like Wayland or Surfaceflinger on Android 49really want an atomic modeset interface, so this is all about the bright 50future. 51 52There is a conversion guide for atomic [1]_ and all you need is a GPU for a 53non-converted driver. The "Atomic mode setting design overview" series [2]_ 54[3]_ at LWN.net can also be helpful. 55 56As part of this drivers also need to convert to universal plane (which means 57exposing primary & cursor as proper plane objects). But that's much easier to 58do by directly using the new atomic helper driver callbacks. 59 60 .. [1] https://blog.ffwll.ch/2014/11/atomic-modeset-support-for-kms-drivers.html 61 .. [2] https://lwn.net/Articles/653071/ 62 .. [3] https://lwn.net/Articles/653466/ 63 64Contact: Daniel Vetter, respective driver maintainers 65 66Level: Advanced 67 68Clean up the clipped coordination confusion around planes 69--------------------------------------------------------- 70 71We have a helper to get this right with drm_plane_helper_check_update(), but 72it's not consistently used. This should be fixed, preferably in the atomic 73helpers (and drivers then moved over to clipped coordinates). Probably the 74helper should also be moved from drm_plane_helper.c to the atomic helpers, to 75avoid confusion - the other helpers in that file are all deprecated legacy 76helpers. 77 78Contact: Ville Syrj��l��, Daniel Vetter, driver maintainers 79 80Level: Advanced 81 82Improve plane atomic_check helpers 83---------------------------------- 84 85Aside from the clipped coordinates right above there's a few suboptimal things 86with the current helpers: 87 88- drm_plane_helper_funcs->atomic_check gets called for enabled or disabled 89 planes. At best this seems to confuse drivers, worst it means they blow up 90 when the plane is disabled without the CRTC. The only special handling is 91 resetting values in the plane state structures, which instead should be moved 92 into the drm_plane_funcs->atomic_duplicate_state functions. 93 94- Once that's done, helpers could stop calling ->atomic_check for disabled 95 planes. 96 97- Then we could go through all the drivers and remove the more-or-less confused 98 checks for plane_state->fb and plane_state->crtc. 99 100Contact: Daniel Vetter 101 102Level: Advanced 103 104Convert early atomic drivers to async commit helpers 105---------------------------------------------------- 106 107For the first year the atomic modeset helpers didn't support asynchronous / 108nonblocking commits, and every driver had to hand-roll them. This is fixed 109now, but there's still a pile of existing drivers that easily could be 110converted over to the new infrastructure. 111 112One issue with the helpers is that they require that drivers handle completion 113events for atomic commits correctly. But fixing these bugs is good anyway. 114 115Somewhat related is the legacy_cursor_update hack, which should be replaced with 116the new atomic_async_check/commit functionality in the helpers in drivers that 117still look at that flag. 118 119Contact: Daniel Vetter, respective driver maintainers 120 121Level: Advanced 122 123Rename drm_atomic_state 124----------------------- 125 126The KMS framework uses two slightly different definitions for the ``state`` 127concept. For a given object (plane, CRTC, encoder, etc., so 128``drm_$OBJECT_state``), the state is the entire state of that object. However, 129at the device level, ``drm_atomic_state`` refers to a state update for a 130limited number of objects. 131 132The state isn't the entire device state, but only the full state of some 133objects in that device. This is confusing to newcomers, and 134``drm_atomic_state`` should be renamed to something clearer like 135``drm_atomic_commit``. 136 137In addition to renaming the structure itself, it would also imply renaming some 138related functions (``drm_atomic_state_alloc``, ``drm_atomic_state_get``, 139``drm_atomic_state_put``, ``drm_atomic_state_init``, 140``__drm_atomic_state_free``, etc.). 141 142Contact: Maxime Ripard <mripard@kernel.org> 143 144Level: Advanced 145 146Fallout from atomic KMS 147----------------------- 148 149``drm_atomic_helper.c`` provides a batch of functions which implement legacy 150IOCTLs on top of the new atomic driver interface. Which is really nice for 151gradual conversion of drivers, but unfortunately the semantic mismatches are 152a bit too severe. So there's some follow-up work to adjust the function 153interfaces to fix these issues: 154 155* atomic needs the lock acquire context. At the moment that's passed around 156 implicitly with some horrible hacks, and it's also allocate with 157 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 158 the acquire context explicitly on stack and then also pass it down into 159 drivers explicitly so that the legacy-on-atomic functions can use them. 160 161 Except for some driver code this is done. This task should be finished by 162 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 163 164* A bunch of the vtable hooks are now in the wrong place: DRM has a split 165 between core vfunc tables (named ``drm_foo_funcs``), which are used to 166 implement the userspace ABI. And then there's the optional hooks for the 167 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 168 internal use. Some of these hooks should be move from ``_funcs`` to 169 ``_helper_funcs`` since they are not part of the core ABI. There's a 170 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 171 172Contact: Daniel Vetter 173 174Level: Intermediate 175 176Get rid of dev->struct_mutex from GEM drivers 177--------------------------------------------- 178 179``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 180everything. Nowadays in modern drivers the only bit where it's mandatory is 181serializing GEM buffer object destruction. Which unfortunately means drivers 182have to keep track of that lock and either call ``unreference`` or 183``unreference_locked`` depending upon context. 184 185Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 186and there's a GEM object ``free`` callback for any drivers which are 187entirely ``struct_mutex`` free. 188 189For drivers that need ``struct_mutex`` it should be replaced with a driver- 190private lock. The tricky part is the BO free functions, since those can't 191reliably take that lock any more. Instead state needs to be protected with 192suitable subordinate locks or some cleanup work pushed to a worker thread. For 193performance-critical drivers it might also be better to go with a more 194fine-grained per-buffer object and per-context lockings scheme. Currently only 195the ``msm`` and `i915` drivers use ``struct_mutex``. 196 197Contact: Daniel Vetter, respective driver maintainers 198 199Level: Advanced 200 201Move Buffer Object Locking to dma_resv_lock() 202--------------------------------------------- 203 204Many drivers have their own per-object locking scheme, usually using 205mutex_lock(). This causes all kinds of trouble for buffer sharing, since 206depending which driver is the exporter and importer, the locking hierarchy is 207reversed. 208 209To solve this we need one standard per-object locking mechanism, which is 210dma_resv_lock(). This lock needs to be called as the outermost lock, with all 211other driver specific per-object locks removed. The problem is that rolling out 212the actual change to the locking contract is a flag day, due to struct dma_buf 213buffer sharing. 214 215Level: Expert 216 217Convert logging to drm_* functions with drm_device parameter 218------------------------------------------------------------ 219 220For drivers which could have multiple instances, it is necessary to 221differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 222don't do this, drivers used dev_info/warn/err to make this differentiation. We 223now have drm_* variants of the drm print functions, so we can start to convert 224those drivers back to using drm-formatted specific log messages. 225 226Before you start this conversion please contact the relevant maintainers to make 227sure your work will be merged - not everyone agrees that the DRM dmesg macros 228are better. 229 230Contact: Sean Paul, Maintainer of the driver you plan to convert 231 232Level: Starter 233 234Convert drivers to use simple modeset suspend/resume 235---------------------------------------------------- 236 237Most drivers (except i915 and nouveau) that use 238drm_atomic_helper_suspend/resume() can probably be converted to use 239drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 240of the atomic suspend/resume code in older atomic modeset drivers. 241 242Contact: Maintainer of the driver you plan to convert 243 244Level: Intermediate 245 246Convert drivers to use drm_fbdev_generic_setup() 247------------------------------------------------ 248 249Most drivers can use drm_fbdev_generic_setup(). Driver have to implement 250atomic modesetting and GEM vmap support. Historically, generic fbdev emulation 251expected the framebuffer in system memory or system-like memory. By employing 252struct iosys_map, drivers with frambuffers in I/O memory can be supported 253as well. 254 255Contact: Maintainer of the driver you plan to convert 256 257Level: Intermediate 258 259Reimplement functions in drm_fbdev_fb_ops without fbdev 260------------------------------------------------------- 261 262A number of callback functions in drm_fbdev_fb_ops could benefit from 263being rewritten without dependencies on the fbdev module. Some of the 264helpers could further benefit from using struct iosys_map instead of 265raw pointers. 266 267Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 268 269Level: Advanced 270 271Benchmark and optimize blitting and format-conversion function 272-------------------------------------------------------------- 273 274Drawing to display memory quickly is crucial for many applications' 275performance. 276 277On at least x86-64, sys_imageblit() is significantly slower than 278cfb_imageblit(), even though both use the same blitting algorithm and 279the latter is written for I/O memory. It turns out that cfb_imageblit() 280uses movl instructions, while sys_imageblit apparently does not. This 281seems to be a problem with gcc's optimizer. DRM's format-conversion 282helpers might be subject to similar issues. 283 284Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion 285helpers. In cases that can be further optimized, maybe implement a different 286algorithm. For micro-optimizations, use movl/movq instructions explicitly. 287That might possibly require architecture-specific helpers (e.g., storel() 288storeq()). 289 290Contact: Thomas Zimmermann <tzimmermann@suse.de> 291 292Level: Intermediate 293 294drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 295----------------------------------------------------------------- 296 297A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 298Various hold-ups: 299 300- Need to switch over to the generic dirty tracking code using 301 drm_atomic_helper_dirtyfb first (e.g. qxl). 302 303- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 304 setup code can't be deleted. 305 306- Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for 307 valid formats for atomic drivers. 308 309- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 310 version of the varios drm_gem_fb_create functions. Maybe called 311 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 312 313Contact: Daniel Vetter 314 315Level: Intermediate 316 317Generic fbdev defio support 318--------------------------- 319 320The defio support code in the fbdev core has some very specific requirements, 321which means drivers need to have a special framebuffer for fbdev. The main 322issue is that it uses some fields in struct page itself, which breaks shmem 323gem objects (and other things). To support defio, affected drivers require 324the use of a shadow buffer, which may add CPU and memory overhead. 325 326Possible solution would be to write our own defio mmap code in the drm fbdev 327emulation. It would need to fully wrap the existing mmap ops, forwarding 328everything after it has done the write-protect/mkwrite trickery: 329 330- In the drm_fbdev_fb_mmap helper, if we need defio, change the 331 default page prots to write-protected with something like this:: 332 333 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 334 335- Set the mkwrite and fsync callbacks with similar implementions to the core 336 fbdev defio stuff. These should all work on plain ptes, they don't actually 337 require a struct page. uff. These should all work on plain ptes, they don't 338 actually require a struct page. 339 340- Track the dirty pages in a separate structure (bitfield with one bit per page 341 should work) to avoid clobbering struct page. 342 343Might be good to also have some igt testcases for this. 344 345Contact: Daniel Vetter, Noralf Tronnes 346 347Level: Advanced 348 349connector register/unregister fixes 350----------------------------------- 351 352- For most connectors it's a no-op to call drm_connector_register/unregister 353 directly from driver code, drm_dev_register/unregister take care of this 354 already. We can remove all of them. 355 356- For dp drivers it's a bit more a mess, since we need the connector to be 357 registered when calling drm_dp_aux_register. Fix this by instead calling 358 drm_dp_aux_init, and moving the actual registering into a late_register 359 callback as recommended in the kerneldoc. 360 361Level: Intermediate 362 363Remove load/unload callbacks 364---------------------------- 365 366The load/unload callbacks in struct &drm_driver are very much midlayers, plus 367for historical reasons they get the ordering wrong (and we can't fix that) 368between setting up the &drm_driver structure and calling drm_dev_register(). 369 370- Rework drivers to no longer use the load/unload callbacks, directly coding the 371 load/unload sequence into the driver's probe function. 372 373- Once all drivers are converted, remove the load/unload callbacks. 374 375Contact: Daniel Vetter 376 377Level: Intermediate 378 379Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 380--------------------------------------------------------------- 381 382Once EDID is parsed, the monitor HDMI support information is available through 383drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 384retrieve the same information, which is less efficient. 385 386Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 387drm_display_info.is_hdmi if applicable. 388 389Contact: Laurent Pinchart, respective driver maintainers 390 391Level: Intermediate 392 393Consolidate custom driver modeset properties 394-------------------------------------------- 395 396Before atomic modeset took place, many drivers where creating their own 397properties. Among other things, atomic brought the requirement that custom, 398driver specific properties should not be used. 399 400For this task, we aim to introduce core helpers or reuse the existing ones 401if available: 402 403A quick, unconfirmed, examples list. 404 405Introduce core helpers: 406- audio (amdgpu, intel, gma500, radeon) 407- brightness, contrast, etc (armada, nouveau) - overlay only (?) 408- broadcast rgb (gma500, intel) 409- colorkey (armada, nouveau, rcar) - overlay only (?) 410- dither (amdgpu, nouveau, radeon) - varies across drivers 411- underscan family (amdgpu, radeon, nouveau) 412 413Already in core: 414- colorspace (sti) 415- tv format names, enhancements (gma500, intel) 416- tv overscan, margins, etc. (gma500, intel) 417- zorder (omapdrm) - same as zpos (?) 418 419 420Contact: Emil Velikov, respective driver maintainers 421 422Level: Intermediate 423 424Use struct iosys_map throughout codebase 425---------------------------------------- 426 427Pointers to shared device memory are stored in struct iosys_map. Each 428instance knows whether it refers to system or I/O memory. Most of the DRM-wide 429interface have been converted to use struct iosys_map, but implementations 430often still use raw pointers. 431 432The task is to use struct iosys_map where it makes sense. 433 434* Memory managers should use struct iosys_map for dma-buf-imported buffers. 435* TTM might benefit from using struct iosys_map internally. 436* Framebuffer copying and blitting helpers should operate on struct iosys_map. 437 438Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian K��nig, Daniel Vetter 439 440Level: Intermediate 441 442Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly 443-------------------------------------------------------------------------------------- 444 445The values in struct drm_mode_config.{max_width,max_height} describe the 446maximum supported framebuffer size. It's the virtual screen size, but many 447drivers treat it like limitations of the physical resolution. 448 449The maximum width depends on the hardware's maximum scanline pitch. The 450maximum height depends on the amount of addressable video memory. Review all 451drivers to initialize the fields to the correct values. 452 453Contact: Thomas Zimmermann <tzimmermann@suse.de> 454 455Level: Intermediate 456 457Request memory regions in all drivers 458------------------------------------- 459 460Go through all drivers and add code to request the memory regions that the 461driver uses. This requires adding calls to request_mem_region(), 462pci_request_region() or similar functions. Use helpers for managed cleanup 463where possible. 464 465Drivers are pretty bad at doing this and there used to be conflicts among 466DRM and fbdev drivers. Still, it's the correct thing to do. 467 468Contact: Thomas Zimmermann <tzimmermann@suse.de> 469 470Level: Starter 471 472Remove driver dependencies on FB_DEVICE 473--------------------------------------- 474 475A number of fbdev drivers provide attributes via sysfs and therefore depend 476on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make 477any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective 478code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not 479all drivers might be able to drop CONFIG_FB_DEVICE. 480 481Contact: Thomas Zimmermann <tzimmermann@suse.de> 482 483Level: Starter 484 485Clean up checks for already prepared/enabled in panels 486------------------------------------------------------ 487 488In a whole pile of panel drivers, we have code to make the 489prepare/unprepare/enable/disable callbacks behave as no-ops if they've already 490been called. To get some idea of the duplicated code, try:: 491 492 git grep 'if.*>prepared' -- drivers/gpu/drm/panel 493 git grep 'if.*>enabled' -- drivers/gpu/drm/panel 494 495In the patch ("drm/panel: Check for already prepared/enabled in drm_panel") 496we've moved this check to the core. Now we can most definitely remove the 497check from the individual panels and save a pile of code. 498 499In adition to removing the check from the individual panels, it is believed 500that even the core shouldn't need this check and that should be considered 501an error if other code ever relies on this check. The check in the core 502currently prints a warning whenever something is relying on this check with 503dev_warn(). After a little while, we likely want to promote this to a 504WARN(1) to help encourage folks not to rely on this behavior. 505 506Contact: Douglas Anderson <dianders@chromium.org> 507 508Level: Starter/Intermediate 509 510 511Core refactorings 512================= 513 514Make panic handling work 515------------------------ 516 517This is a really varied tasks with lots of little bits and pieces: 518 519* The panic path can't be tested currently, leading to constant breaking. The 520 main issue here is that panics can be triggered from hardirq contexts and 521 hence all panic related callback can run in hardirq context. It would be 522 awesome if we could test at least the fbdev helper code and driver code by 523 e.g. trigger calls through drm debugfs files. hardirq context could be 524 achieved by using an IPI to the local processor. 525 526* There's a massive confusion of different panic handlers. DRM fbdev emulation 527 helpers had their own (long removed), but on top of that the fbcon code itself 528 also has one. We need to make sure that they stop fighting over each other. 529 This is worked around by checking ``oops_in_progress`` at various entry points 530 into the DRM fbdev emulation helpers. A much cleaner approach here would be to 531 switch fbcon to the `threaded printk support 532 <https://lwn.net/Articles/800946/>`_. 533 534* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 535 isn't a full solution for panic paths. We need to make sure that it only 536 returns true if there's a panic going on for real, and fix up all the 537 fallout. 538 539* The panic handler must never sleep, which also means it can't ever 540 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 541 even spinlocks (because NMI and hardirq can panic too). We need to either 542 make sure to not call such paths, or trylock everything. Really tricky. 543 544* A clean solution would be an entirely separate panic output support in KMS, 545 bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling 546 <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_. 547 548* Encoding the actual oops and preceding dmesg in a QR might help with the 549 dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages 550 transfer using QR codes 551 <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_ 552 for some example code that could be reused. 553 554Contact: Daniel Vetter 555 556Level: Advanced 557 558Clean up the debugfs support 559---------------------------- 560 561There's a bunch of issues with it: 562 563- Convert drivers to support the drm_debugfs_add_files() function instead of 564 the drm_debugfs_create_files() function. 565 566- Improve late-register debugfs by rolling out the same debugfs pre-register 567 infrastructure for connector and crtc too. That way, the drivers won't need to 568 split their setup code into init and register anymore. 569 570- We probably want to have some support for debugfs files on crtc/connectors and 571 maybe other kms objects directly in core. There's even drm_print support in 572 the funcs for these objects to dump kms state, so it's all there. And then the 573 ->show() functions should obviously give you a pointer to the right object. 574 575- The drm_driver->debugfs_init hooks we have is just an artifact of the old 576 midlayered load sequence. DRM debugfs should work more like sysfs, where you 577 can create properties/files for an object anytime you want, and the core 578 takes care of publishing/unpuplishing all the files at register/unregister 579 time. Drivers shouldn't need to worry about these technicalities, and fixing 580 this (together with the drm_minor->drm_device move) would allow us to remove 581 debugfs_init. 582 583Contact: Daniel Vetter 584 585Level: Intermediate 586 587Object lifetime fixes 588--------------------- 589 590There's two related issues here 591 592- Cleanup up the various ->destroy callbacks, which often are all the same 593 simple code. 594 595- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, 596 which results in use-after free issues on driver unload. This can be serious 597 trouble even for drivers for hardware integrated on the SoC due to 598 EPROBE_DEFERRED backoff. 599 600Both these problems can be solved by switching over to drmm_kzalloc(), and the 601various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), 602drmm_universal_plane_alloc(), ... and so on. 603 604Contact: Daniel Vetter 605 606Level: Intermediate 607 608Remove automatic page mapping from dma-buf importing 609---------------------------------------------------- 610 611When importing dma-bufs, the dma-buf and PRIME frameworks automatically map 612imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and 613drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() 614even if they never do actual device DMA, but only CPU access through 615dma_buf_vmap(). This is a problem for USB devices, which do not support DMA 616operations. 617 618To fix the issue, automatic page mappings should be removed from the 619buffer-sharing code. Fixing this is a bit more involved, since the import/export 620cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over 621this problem for USB devices by fishing out the USB host controller device, as 622long as that supports DMA. Otherwise importing can still needlessly fail. 623 624Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 625 626Level: Advanced 627 628 629Better Testing 630============== 631 632Add unit tests using the Kernel Unit Testing (KUnit) framework 633-------------------------------------------------------------- 634 635The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ 636provides a common framework for unit tests within the Linux kernel. Having a 637test suite would allow to identify regressions earlier. 638 639A good candidate for the first unit tests are the format-conversion helpers in 640``drm_format_helper.c``. 641 642Contact: Javier Martinez Canillas <javierm@redhat.com> 643 644Level: Intermediate 645 646Clean up and document former selftests suites 647--------------------------------------------- 648 649Some KUnit test suites (drm_buddy, drm_cmdline_parser, drm_damage_helper, 650drm_format, drm_framebuffer, drm_dp_mst_helper, drm_mm, drm_plane_helper and 651drm_rect) are former selftests suites that have been converted over when KUnit 652was first introduced. 653 654These suites were fairly undocumented, and with different goals than what unit 655tests can be. Trying to identify what each test in these suites actually test 656for, whether that makes sense for a unit test, and either remove it if it 657doesn't or document it if it does would be of great help. 658 659Contact: Maxime Ripard <mripard@kernel.org> 660 661Level: Intermediate 662 663Enable trinity for DRM 664---------------------- 665 666And fix up the fallout. Should be really interesting ... 667 668Level: Advanced 669 670Make KMS tests in i-g-t generic 671------------------------------- 672 673The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 674including tons of testcases for corner-cases in the modesetting API. It would 675be awesome if those tests (at least the ones not relying on Intel-specific GEM 676features) could be made to run on any KMS driver. 677 678Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 679converting things over. For modeset tests we also first need a bit of 680infrastructure to use dumb buffers for untiled buffers, to be able to run all 681the non-i915 specific modeset tests. 682 683Level: Advanced 684 685Extend virtual test driver (VKMS) 686--------------------------------- 687 688See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 689internship task, since it only requires a virtual machine and can be sized to 690fit the available time. 691 692Level: See details 693 694Backlight Refactoring 695--------------------- 696 697Backlight drivers have a triple enable/disable state, which is a bit overkill. 698Plan to fix this: 699 7001. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 701 has started already. 7022. In all, only look at one of the three status bits set by the above helpers. 7033. Remove the other two status bits. 704 705Contact: Daniel Vetter 706 707Level: Intermediate 708 709Driver Specific 710=============== 711 712AMD DC Display Driver 713--------------------- 714 715AMD DC is the display driver for AMD devices starting with Vega. There has been 716a bunch of progress cleaning it up but there's still plenty of work to be done. 717 718See drivers/gpu/drm/amd/display/TODO for tasks. 719 720Contact: Harry Wentland, Alex Deucher 721 722Bootsplash 723========== 724 725There is support in place now for writing internal DRM clients making it 726possible to pick up the bootsplash work that was rejected because it was written 727for fbdev. 728 729- [v6,8/8] drm/client: Hack: Add bootsplash example 730 https://patchwork.freedesktop.org/patch/306579/ 731 732- [RFC PATCH v2 00/13] Kernel based bootsplash 733 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de 734 735Contact: Sam Ravnborg 736 737Level: Advanced 738 739Brightness handling on devices with multiple internal panels 740============================================================ 741 742On x86/ACPI devices there can be multiple backlight firmware interfaces: 743(ACPI) video, vendor specific and others. As well as direct/native (PWM) 744register programming by the KMS driver. 745 746To deal with this backlight drivers used on x86/ACPI call 747acpi_video_get_backlight_type() which has heuristics (+quirks) to select 748which backlight interface to use; and backlight drivers which do not match 749the returned type will not register themselves, so that only one backlight 750device gets registered (in a single GPU setup, see below). 751 752At the moment this more or less assumes that there will only 753be 1 (internal) panel on a system. 754 755On systems with 2 panels this may be a problem, depending on 756what interface acpi_video_get_backlight_type() selects: 757 7581. native: in this case the KMS driver is expected to know which backlight 759 device belongs to which output so everything should just work. 7602. video: this does support controlling multiple backlights, but some work 761 will need to be done to get the output <-> backlight device mapping 762 763The above assumes both panels will require the same backlight interface type. 764Things will break on systems with multiple panels where the 2 panels need 765a different type of control. E.g. one panel needs ACPI video backlight control, 766where as the other is using native backlight control. Currently in this case 767only one of the 2 required backlight devices will get registered, based on 768the acpi_video_get_backlight_type() return value. 769 770If this (theoretical) case ever shows up, then supporting this will need some 771work. A possible solution here would be to pass a device and connector-name 772to acpi_video_get_backlight_type() so that it can deal with this. 773 774Note in a way we already have a case where userspace sees 2 panels, 775in dual GPU laptop setups with a mux. On those systems we may see 776either 2 native backlight devices; or 2 native backlight devices. 777 778Userspace already has code to deal with this by detecting if the related 779panel is active (iow which way the mux between the GPU and the panels 780points) and then uses that backlight device. Userspace here very much 781assumes a single panel though. It picks only 1 of the 2 backlight devices 782and then only uses that one. 783 784Note that all userspace code (that I know off) is currently hardcoded 785to assume a single panel. 786 787Before the recent changes to not register multiple (e.g. video + native) 788/sys/class/backlight devices for a single panel (on a single GPU laptop), 789userspace would see multiple backlight devices all controlling the same 790backlight. 791 792To deal with this userspace had to always picks one preferred device under 793/sys/class/backlight and will ignore the others. So to support brightness 794control on multiple panels userspace will need to be updated too. 795 796There are plans to allow brightness control through the KMS API by adding 797a "display brightness" property to drm_connector objects for panels. This 798solves a number of issues with the /sys/class/backlight API, including not 799being able to map a sysfs backlight device to a specific connector. Any 800userspace changes to add support for brightness control on devices with 801multiple panels really should build on top of this new KMS property. 802 803Contact: Hans de Goede 804 805Level: Advanced 806 807Buffer age or other damage accumulation algorithm for buffer damage 808=================================================================== 809 810Drivers that do per-buffer uploads, need a buffer damage handling (rather than 811frame damage like drivers that do per-plane or per-CRTC uploads), but there is 812no support to get the buffer age or any other damage accumulation algorithm. 813 814For this reason, the damage helpers just fallback to a full plane update if the 815framebuffer attached to a plane has changed since the last page-flip. Drivers 816set &drm_plane_state.ignore_damage_clips to true as indication to 817drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next() 818helpers that the damage clips should be ignored. 819 820This should be improved to get damage tracking properly working on drivers that 821do per-buffer uploads. 822 823More information about damage tracking and references to learning materials can 824be found in :ref:`damage_tracking_properties`. 825 826Contact: Javier Martinez Canillas <javierm@redhat.com> 827 828Level: Advanced 829 830Outside DRM 831=========== 832 833Convert fbdev drivers to DRM 834---------------------------- 835 836There are plenty of fbdev drivers for older hardware. Some hardware has 837become obsolete, but some still provides good(-enough) framebuffers. The 838drivers that are still useful should be converted to DRM and afterwards 839removed from fbdev. 840 841Very simple fbdev drivers can best be converted by starting with a new 842DRM driver. Simple KMS helpers and SHMEM should be able to handle any 843existing hardware. The new driver's call-back functions are filled from 844existing fbdev code. 845 846More complex fbdev drivers can be refactored step-by-step into a DRM 847driver with the help of the DRM fbconv helpers [4]_. These helpers provide 848the transition layer between the DRM core infrastructure and the fbdev 849driver interface. Create a new DRM driver on top of the fbconv helpers, 850copy over the fbdev driver, and hook it up to the DRM code. Examples for 851several fbdev drivers are available in Thomas Zimmermann's fbconv tree 852[4]_, as well as a tutorial of this process [5]_. The result is a primitive 853DRM driver that can run X11 and Weston. 854 855 .. [4] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 856 .. [5] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 857 858Contact: Thomas Zimmermann <tzimmermann@suse.de> 859 860Level: Advanced 861