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instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Level: Intermediate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 Syrjälä, 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 123Fallout from atomic KMS 124----------------------- 125 126``drm_atomic_helper.c`` provides a batch of functions which implement legacy 127IOCTLs on top of the new atomic driver interface. Which is really nice for 128gradual conversion of drivers, but unfortunately the semantic mismatches are 129a bit too severe. So there's some follow-up work to adjust the function 130interfaces to fix these issues: 131 132* atomic needs the lock acquire context. At the moment that's passed around 133 implicitly with some horrible hacks, and it's also allocate with 134 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 135 the acquire context explicitly on stack and then also pass it down into 136 drivers explicitly so that the legacy-on-atomic functions can use them. 137 138 Except for some driver code this is done. This task should be finished by 139 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 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 149Contact: Daniel Vetter 150 151Level: Intermediate 152 153Get rid of dev->struct_mutex from GEM drivers 154--------------------------------------------- 155 156``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 157everything. Nowadays in modern drivers the only bit where it's mandatory is 158serializing GEM buffer object destruction. Which unfortunately means drivers 159have to keep track of that lock and either call ``unreference`` or 160``unreference_locked`` depending upon context. 161 162Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 163and there's a GEM object ``free`` callback for any drivers which are 164entirely ``struct_mutex`` free. 165 166For drivers that need ``struct_mutex`` it should be replaced with a driver- 167private lock. The tricky part is the BO free functions, since those can't 168reliably take that lock any more. Instead state needs to be protected with 169suitable subordinate locks or some cleanup work pushed to a worker thread. For 170performance-critical drivers it might also be better to go with a more 171fine-grained per-buffer object and per-context lockings scheme. Currently only 172the ``msm`` and `i915` drivers use ``struct_mutex``. 173 174Contact: Daniel Vetter, respective driver maintainers 175 176Level: Advanced 177 178Move Buffer Object Locking to dma_resv_lock() 179--------------------------------------------- 180 181Many drivers have their own per-object locking scheme, usually using 182mutex_lock(). This causes all kinds of trouble for buffer sharing, since 183depending which driver is the exporter and importer, the locking hierarchy is 184reversed. 185 186To solve this we need one standard per-object locking mechanism, which is 187dma_resv_lock(). This lock needs to be called as the outermost lock, with all 188other driver specific per-object locks removed. The problem is that rolling out 189the actual change to the locking contract is a flag day, due to struct dma_buf 190buffer sharing. 191 192Level: Expert 193 194Convert logging to drm_* functions with drm_device parameter 195------------------------------------------------------------ 196 197For drivers which could have multiple instances, it is necessary to 198differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 199don't do this, drivers used dev_info/warn/err to make this differentiation. We 200now have drm_* variants of the drm print functions, so we can start to convert 201those drivers back to using drm-formatted specific log messages. 202 203Before you start this conversion please contact the relevant maintainers to make 204sure your work will be merged - not everyone agrees that the DRM dmesg macros 205are better. 206 207Contact: Sean Paul, Maintainer of the driver you plan to convert 208 209Level: Starter 210 211Convert drivers to use simple modeset suspend/resume 212---------------------------------------------------- 213 214Most drivers (except i915 and nouveau) that use 215drm_atomic_helper_suspend/resume() can probably be converted to use 216drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 217of the atomic suspend/resume code in older atomic modeset drivers. 218 219Contact: Maintainer of the driver you plan to convert 220 221Level: Intermediate 222 223Convert drivers to use drm_fbdev_generic_setup() 224------------------------------------------------ 225 226Most drivers can use drm_fbdev_generic_setup(). Driver have to implement 227atomic modesetting and GEM vmap support. Historically, generic fbdev emulation 228expected the framebuffer in system memory or system-like memory. By employing 229struct iosys_map, drivers with frambuffers in I/O memory can be supported 230as well. 231 232Contact: Maintainer of the driver you plan to convert 233 234Level: Intermediate 235 236Reimplement functions in drm_fbdev_fb_ops without fbdev 237------------------------------------------------------- 238 239A number of callback functions in drm_fbdev_fb_ops could benefit from 240being rewritten without dependencies on the fbdev module. Some of the 241helpers could further benefit from using struct iosys_map instead of 242raw pointers. 243 244Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 245 246Level: Advanced 247 248Benchmark and optimize blitting and format-conversion function 249-------------------------------------------------------------- 250 251Drawing to display memory quickly is crucial for many applications' 252performance. 253 254On at least x86-64, sys_imageblit() is significantly slower than 255cfb_imageblit(), even though both use the same blitting algorithm and 256the latter is written for I/O memory. It turns out that cfb_imageblit() 257uses movl instructions, while sys_imageblit apparently does not. This 258seems to be a problem with gcc's optimizer. DRM's format-conversion 259helpers might be subject to similar issues. 260 261Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion 262helpers. In cases that can be further optimized, maybe implement a different 263algorithm. For micro-optimizations, use movl/movq instructions explicitly. 264That might possibly require architecture-specific helpers (e.g., storel() 265storeq()). 266 267Contact: Thomas Zimmermann <tzimmermann@suse.de> 268 269Level: Intermediate 270 271drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 272----------------------------------------------------------------- 273 274A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 275Various hold-ups: 276 277- Need to switch over to the generic dirty tracking code using 278 drm_atomic_helper_dirtyfb first (e.g. qxl). 279 280- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 281 setup code can't be deleted. 282 283- Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for 284 valid formats for atomic drivers. 285 286- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 287 version of the varios drm_gem_fb_create functions. Maybe called 288 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 289 290Contact: Daniel Vetter 291 292Level: Intermediate 293 294Generic fbdev defio support 295--------------------------- 296 297The defio support code in the fbdev core has some very specific requirements, 298which means drivers need to have a special framebuffer for fbdev. The main 299issue is that it uses some fields in struct page itself, which breaks shmem 300gem objects (and other things). To support defio, affected drivers require 301the use of a shadow buffer, which may add CPU and memory overhead. 302 303Possible solution would be to write our own defio mmap code in the drm fbdev 304emulation. It would need to fully wrap the existing mmap ops, forwarding 305everything after it has done the write-protect/mkwrite trickery: 306 307- In the drm_fbdev_fb_mmap helper, if we need defio, change the 308 default page prots to write-protected with something like this:: 309 310 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 311 312- Set the mkwrite and fsync callbacks with similar implementions to the core 313 fbdev defio stuff. These should all work on plain ptes, they don't actually 314 require a struct page. uff. These should all work on plain ptes, they don't 315 actually require a struct page. 316 317- Track the dirty pages in a separate structure (bitfield with one bit per page 318 should work) to avoid clobbering struct page. 319 320Might be good to also have some igt testcases for this. 321 322Contact: Daniel Vetter, Noralf Tronnes 323 324Level: Advanced 325 326connector register/unregister fixes 327----------------------------------- 328 329- For most connectors it's a no-op to call drm_connector_register/unregister 330 directly from driver code, drm_dev_register/unregister take care of this 331 already. We can remove all of them. 332 333- For dp drivers it's a bit more a mess, since we need the connector to be 334 registered when calling drm_dp_aux_register. Fix this by instead calling 335 drm_dp_aux_init, and moving the actual registering into a late_register 336 callback as recommended in the kerneldoc. 337 338Level: Intermediate 339 340Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 341--------------------------------------------------------------- 342 343The load/unload callbacks in struct &drm_driver are very much midlayers, plus 344for historical reasons they get the ordering wrong (and we can't fix that) 345between setting up the &drm_driver structure and calling drm_dev_register(). 346 347- Rework drivers to no longer use the load/unload callbacks, directly coding the 348 load/unload sequence into the driver's probe function. 349 350- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 351 callbacks for all modern drivers. 352 353Contact: Daniel Vetter 354 355Level: Intermediate 356 357Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 358--------------------------------------------------------------- 359 360Once EDID is parsed, the monitor HDMI support information is available through 361drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 362retrieve the same information, which is less efficient. 363 364Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 365drm_display_info.is_hdmi if applicable. 366 367Contact: Laurent Pinchart, respective driver maintainers 368 369Level: Intermediate 370 371Consolidate custom driver modeset properties 372-------------------------------------------- 373 374Before atomic modeset took place, many drivers where creating their own 375properties. Among other things, atomic brought the requirement that custom, 376driver specific properties should not be used. 377 378For this task, we aim to introduce core helpers or reuse the existing ones 379if available: 380 381A quick, unconfirmed, examples list. 382 383Introduce core helpers: 384- audio (amdgpu, intel, gma500, radeon) 385- brightness, contrast, etc (armada, nouveau) - overlay only (?) 386- broadcast rgb (gma500, intel) 387- colorkey (armada, nouveau, rcar) - overlay only (?) 388- dither (amdgpu, nouveau, radeon) - varies across drivers 389- underscan family (amdgpu, radeon, nouveau) 390 391Already in core: 392- colorspace (sti) 393- tv format names, enhancements (gma500, intel) 394- tv overscan, margins, etc. (gma500, intel) 395- zorder (omapdrm) - same as zpos (?) 396 397 398Contact: Emil Velikov, respective driver maintainers 399 400Level: Intermediate 401 402Use struct iosys_map throughout codebase 403---------------------------------------- 404 405Pointers to shared device memory are stored in struct iosys_map. Each 406instance knows whether it refers to system or I/O memory. Most of the DRM-wide 407interface have been converted to use struct iosys_map, but implementations 408often still use raw pointers. 409 410The task is to use struct iosys_map where it makes sense. 411 412* Memory managers should use struct iosys_map for dma-buf-imported buffers. 413* TTM might benefit from using struct iosys_map internally. 414* Framebuffer copying and blitting helpers should operate on struct iosys_map. 415 416Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Daniel Vetter 417 418Level: Intermediate 419 420Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly 421-------------------------------------------------------------------------------------- 422 423The values in struct drm_mode_config.{max_width,max_height} describe the 424maximum supported framebuffer size. It's the virtual screen size, but many 425drivers treat it like limitations of the physical resolution. 426 427The maximum width depends on the hardware's maximum scanline pitch. The 428maximum height depends on the amount of addressable video memory. Review all 429drivers to initialize the fields to the correct values. 430 431Contact: Thomas Zimmermann <tzimmermann@suse.de> 432 433Level: Intermediate 434 435Request memory regions in all drivers 436------------------------------------- 437 438Go through all drivers and add code to request the memory regions that the 439driver uses. This requires adding calls to request_mem_region(), 440pci_request_region() or similar functions. Use helpers for managed cleanup 441where possible. 442 443Drivers are pretty bad at doing this and there used to be conflicts among 444DRM and fbdev drivers. Still, it's the correct thing to do. 445 446Contact: Thomas Zimmermann <tzimmermann@suse.de> 447 448Level: Starter 449 450Remove driver dependencies on FB_DEVICE 451--------------------------------------- 452 453A number of fbdev drivers provide attributes via sysfs and therefore depend 454on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make 455any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective 456code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not 457all drivers might be able to drop CONFIG_FB_DEVICE. 458 459Contact: Thomas Zimmermann <tzimmermann@suse.de> 460 461Level: Starter 462 463Clean up checks for already prepared/enabled in panels 464------------------------------------------------------ 465 466In a whole pile of panel drivers, we have code to make the 467prepare/unprepare/enable/disable callbacks behave as no-ops if they've already 468been called. To get some idea of the duplicated code, try:: 469 470 git grep 'if.*>prepared' -- drivers/gpu/drm/panel 471 git grep 'if.*>enabled' -- drivers/gpu/drm/panel 472 473In the patch ("drm/panel: Check for already prepared/enabled in drm_panel") 474we've moved this check to the core. Now we can most definitely remove the 475check from the individual panels and save a pile of code. 476 477In adition to removing the check from the individual panels, it is believed 478that even the core shouldn't need this check and that should be considered 479an error if other code ever relies on this check. The check in the core 480currently prints a warning whenever something is relying on this check with 481dev_warn(). After a little while, we likely want to promote this to a 482WARN(1) to help encourage folks not to rely on this behavior. 483 484Contact: Douglas Anderson <dianders@chromium.org> 485 486Level: Starter/Intermediate 487 488 489Core refactorings 490================= 491 492Make panic handling work 493------------------------ 494 495This is a really varied tasks with lots of little bits and pieces: 496 497* The panic path can't be tested currently, leading to constant breaking. The 498 main issue here is that panics can be triggered from hardirq contexts and 499 hence all panic related callback can run in hardirq context. It would be 500 awesome if we could test at least the fbdev helper code and driver code by 501 e.g. trigger calls through drm debugfs files. hardirq context could be 502 achieved by using an IPI to the local processor. 503 504* There's a massive confusion of different panic handlers. DRM fbdev emulation 505 helpers had their own (long removed), but on top of that the fbcon code itself 506 also has one. We need to make sure that they stop fighting over each other. 507 This is worked around by checking ``oops_in_progress`` at various entry points 508 into the DRM fbdev emulation helpers. A much cleaner approach here would be to 509 switch fbcon to the `threaded printk support 510 <https://lwn.net/Articles/800946/>`_. 511 512* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 513 isn't a full solution for panic paths. We need to make sure that it only 514 returns true if there's a panic going on for real, and fix up all the 515 fallout. 516 517* The panic handler must never sleep, which also means it can't ever 518 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 519 even spinlocks (because NMI and hardirq can panic too). We need to either 520 make sure to not call such paths, or trylock everything. Really tricky. 521 522* A clean solution would be an entirely separate panic output support in KMS, 523 bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling 524 <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_. 525 526* Encoding the actual oops and preceding dmesg in a QR might help with the 527 dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages 528 transfer using QR codes 529 <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_ 530 for some example code that could be reused. 531 532Contact: Daniel Vetter 533 534Level: Advanced 535 536Clean up the debugfs support 537---------------------------- 538 539There's a bunch of issues with it: 540 541- Convert drivers to support the drm_debugfs_add_files() function instead of 542 the drm_debugfs_create_files() function. 543 544- Improve late-register debugfs by rolling out the same debugfs pre-register 545 infrastructure for connector and crtc too. That way, the drivers won't need to 546 split their setup code into init and register anymore. 547 548- We probably want to have some support for debugfs files on crtc/connectors and 549 maybe other kms objects directly in core. There's even drm_print support in 550 the funcs for these objects to dump kms state, so it's all there. And then the 551 ->show() functions should obviously give you a pointer to the right object. 552 553- The drm_driver->debugfs_init hooks we have is just an artifact of the old 554 midlayered load sequence. DRM debugfs should work more like sysfs, where you 555 can create properties/files for an object anytime you want, and the core 556 takes care of publishing/unpuplishing all the files at register/unregister 557 time. Drivers shouldn't need to worry about these technicalities, and fixing 558 this (together with the drm_minor->drm_device move) would allow us to remove 559 debugfs_init. 560 561Contact: Daniel Vetter 562 563Level: Intermediate 564 565Object lifetime fixes 566--------------------- 567 568There's two related issues here 569 570- Cleanup up the various ->destroy callbacks, which often are all the same 571 simple code. 572 573- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, 574 which results in use-after free issues on driver unload. This can be serious 575 trouble even for drivers for hardware integrated on the SoC due to 576 EPROBE_DEFERRED backoff. 577 578Both these problems can be solved by switching over to drmm_kzalloc(), and the 579various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), 580drmm_universal_plane_alloc(), ... and so on. 581 582Contact: Daniel Vetter 583 584Level: Intermediate 585 586Remove automatic page mapping from dma-buf importing 587---------------------------------------------------- 588 589When importing dma-bufs, the dma-buf and PRIME frameworks automatically map 590imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and 591drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() 592even if they never do actual device DMA, but only CPU access through 593dma_buf_vmap(). This is a problem for USB devices, which do not support DMA 594operations. 595 596To fix the issue, automatic page mappings should be removed from the 597buffer-sharing code. Fixing this is a bit more involved, since the import/export 598cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over 599this problem for USB devices by fishing out the USB host controller device, as 600long as that supports DMA. Otherwise importing can still needlessly fail. 601 602Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 603 604Level: Advanced 605 606 607Better Testing 608============== 609 610Add unit tests using the Kernel Unit Testing (KUnit) framework 611-------------------------------------------------------------- 612 613The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ 614provides a common framework for unit tests within the Linux kernel. Having a 615test suite would allow to identify regressions earlier. 616 617A good candidate for the first unit tests are the format-conversion helpers in 618``drm_format_helper.c``. 619 620Contact: Javier Martinez Canillas <javierm@redhat.com> 621 622Level: Intermediate 623 624Enable trinity for DRM 625---------------------- 626 627And fix up the fallout. Should be really interesting ... 628 629Level: Advanced 630 631Make KMS tests in i-g-t generic 632------------------------------- 633 634The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 635including tons of testcases for corner-cases in the modesetting API. It would 636be awesome if those tests (at least the ones not relying on Intel-specific GEM 637features) could be made to run on any KMS driver. 638 639Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 640converting things over. For modeset tests we also first need a bit of 641infrastructure to use dumb buffers for untiled buffers, to be able to run all 642the non-i915 specific modeset tests. 643 644Level: Advanced 645 646Extend virtual test driver (VKMS) 647--------------------------------- 648 649See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 650internship task, since it only requires a virtual machine and can be sized to 651fit the available time. 652 653Level: See details 654 655Backlight Refactoring 656--------------------- 657 658Backlight drivers have a triple enable/disable state, which is a bit overkill. 659Plan to fix this: 660 6611. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 662 has started already. 6632. In all, only look at one of the three status bits set by the above helpers. 6643. Remove the other two status bits. 665 666Contact: Daniel Vetter 667 668Level: Intermediate 669 670Driver Specific 671=============== 672 673AMD DC Display Driver 674--------------------- 675 676AMD DC is the display driver for AMD devices starting with Vega. There has been 677a bunch of progress cleaning it up but there's still plenty of work to be done. 678 679See drivers/gpu/drm/amd/display/TODO for tasks. 680 681Contact: Harry Wentland, Alex Deucher 682 683Bootsplash 684========== 685 686There is support in place now for writing internal DRM clients making it 687possible to pick up the bootsplash work that was rejected because it was written 688for fbdev. 689 690- [v6,8/8] drm/client: Hack: Add bootsplash example 691 https://patchwork.freedesktop.org/patch/306579/ 692 693- [RFC PATCH v2 00/13] Kernel based bootsplash 694 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de 695 696Contact: Sam Ravnborg 697 698Level: Advanced 699 700Brightness handling on devices with multiple internal panels 701============================================================ 702 703On x86/ACPI devices there can be multiple backlight firmware interfaces: 704(ACPI) video, vendor specific and others. As well as direct/native (PWM) 705register programming by the KMS driver. 706 707To deal with this backlight drivers used on x86/ACPI call 708acpi_video_get_backlight_type() which has heuristics (+quirks) to select 709which backlight interface to use; and backlight drivers which do not match 710the returned type will not register themselves, so that only one backlight 711device gets registered (in a single GPU setup, see below). 712 713At the moment this more or less assumes that there will only 714be 1 (internal) panel on a system. 715 716On systems with 2 panels this may be a problem, depending on 717what interface acpi_video_get_backlight_type() selects: 718 7191. native: in this case the KMS driver is expected to know which backlight 720 device belongs to which output so everything should just work. 7212. video: this does support controlling multiple backlights, but some work 722 will need to be done to get the output <-> backlight device mapping 723 724The above assumes both panels will require the same backlight interface type. 725Things will break on systems with multiple panels where the 2 panels need 726a different type of control. E.g. one panel needs ACPI video backlight control, 727where as the other is using native backlight control. Currently in this case 728only one of the 2 required backlight devices will get registered, based on 729the acpi_video_get_backlight_type() return value. 730 731If this (theoretical) case ever shows up, then supporting this will need some 732work. A possible solution here would be to pass a device and connector-name 733to acpi_video_get_backlight_type() so that it can deal with this. 734 735Note in a way we already have a case where userspace sees 2 panels, 736in dual GPU laptop setups with a mux. On those systems we may see 737either 2 native backlight devices; or 2 native backlight devices. 738 739Userspace already has code to deal with this by detecting if the related 740panel is active (iow which way the mux between the GPU and the panels 741points) and then uses that backlight device. Userspace here very much 742assumes a single panel though. It picks only 1 of the 2 backlight devices 743and then only uses that one. 744 745Note that all userspace code (that I know off) is currently hardcoded 746to assume a single panel. 747 748Before the recent changes to not register multiple (e.g. video + native) 749/sys/class/backlight devices for a single panel (on a single GPU laptop), 750userspace would see multiple backlight devices all controlling the same 751backlight. 752 753To deal with this userspace had to always picks one preferred device under 754/sys/class/backlight and will ignore the others. So to support brightness 755control on multiple panels userspace will need to be updated too. 756 757There are plans to allow brightness control through the KMS API by adding 758a "display brightness" property to drm_connector objects for panels. This 759solves a number of issues with the /sys/class/backlight API, including not 760being able to map a sysfs backlight device to a specific connector. Any 761userspace changes to add support for brightness control on devices with 762multiple panels really should build on top of this new KMS property. 763 764Contact: Hans de Goede 765 766Level: Advanced 767 768Outside DRM 769=========== 770 771Convert fbdev drivers to DRM 772---------------------------- 773 774There are plenty of fbdev drivers for older hardware. Some hardware has 775become obsolete, but some still provides good(-enough) framebuffers. The 776drivers that are still useful should be converted to DRM and afterwards 777removed from fbdev. 778 779Very simple fbdev drivers can best be converted by starting with a new 780DRM driver. Simple KMS helpers and SHMEM should be able to handle any 781existing hardware. The new driver's call-back functions are filled from 782existing fbdev code. 783 784More complex fbdev drivers can be refactored step-by-step into a DRM 785driver with the help of the DRM fbconv helpers [4]_. These helpers provide 786the transition layer between the DRM core infrastructure and the fbdev 787driver interface. Create a new DRM driver on top of the fbconv helpers, 788copy over the fbdev driver, and hook it up to the DRM code. Examples for 789several fbdev drivers are available in Thomas Zimmermann's fbconv tree 790[4]_, as well as a tutorial of this process [5]_. The result is a primitive 791DRM driver that can run X11 and Weston. 792 793 .. [4] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 794 .. [5] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 795 796Contact: Thomas Zimmermann <tzimmermann@suse.de> 797 798Level: Advanced 799