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instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Level: Intermediate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 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 drivers are converted, remove the load/unload callbacks. 351 352Contact: Daniel Vetter 353 354Level: Intermediate 355 356Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 357--------------------------------------------------------------- 358 359Once EDID is parsed, the monitor HDMI support information is available through 360drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 361retrieve the same information, which is less efficient. 362 363Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 364drm_display_info.is_hdmi if applicable. 365 366Contact: Laurent Pinchart, respective driver maintainers 367 368Level: Intermediate 369 370Consolidate custom driver modeset properties 371-------------------------------------------- 372 373Before atomic modeset took place, many drivers where creating their own 374properties. Among other things, atomic brought the requirement that custom, 375driver specific properties should not be used. 376 377For this task, we aim to introduce core helpers or reuse the existing ones 378if available: 379 380A quick, unconfirmed, examples list. 381 382Introduce core helpers: 383- audio (amdgpu, intel, gma500, radeon) 384- brightness, contrast, etc (armada, nouveau) - overlay only (?) 385- broadcast rgb (gma500, intel) 386- colorkey (armada, nouveau, rcar) - overlay only (?) 387- dither (amdgpu, nouveau, radeon) - varies across drivers 388- underscan family (amdgpu, radeon, nouveau) 389 390Already in core: 391- colorspace (sti) 392- tv format names, enhancements (gma500, intel) 393- tv overscan, margins, etc. (gma500, intel) 394- zorder (omapdrm) - same as zpos (?) 395 396 397Contact: Emil Velikov, respective driver maintainers 398 399Level: Intermediate 400 401Use struct iosys_map throughout codebase 402---------------------------------------- 403 404Pointers to shared device memory are stored in struct iosys_map. Each 405instance knows whether it refers to system or I/O memory. Most of the DRM-wide 406interface have been converted to use struct iosys_map, but implementations 407often still use raw pointers. 408 409The task is to use struct iosys_map where it makes sense. 410 411* Memory managers should use struct iosys_map for dma-buf-imported buffers. 412* TTM might benefit from using struct iosys_map internally. 413* Framebuffer copying and blitting helpers should operate on struct iosys_map. 414 415Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Daniel Vetter 416 417Level: Intermediate 418 419Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly 420-------------------------------------------------------------------------------------- 421 422The values in struct drm_mode_config.{max_width,max_height} describe the 423maximum supported framebuffer size. It's the virtual screen size, but many 424drivers treat it like limitations of the physical resolution. 425 426The maximum width depends on the hardware's maximum scanline pitch. The 427maximum height depends on the amount of addressable video memory. Review all 428drivers to initialize the fields to the correct values. 429 430Contact: Thomas Zimmermann <tzimmermann@suse.de> 431 432Level: Intermediate 433 434Request memory regions in all drivers 435------------------------------------- 436 437Go through all drivers and add code to request the memory regions that the 438driver uses. This requires adding calls to request_mem_region(), 439pci_request_region() or similar functions. Use helpers for managed cleanup 440where possible. 441 442Drivers are pretty bad at doing this and there used to be conflicts among 443DRM and fbdev drivers. Still, it's the correct thing to do. 444 445Contact: Thomas Zimmermann <tzimmermann@suse.de> 446 447Level: Starter 448 449Remove driver dependencies on FB_DEVICE 450--------------------------------------- 451 452A number of fbdev drivers provide attributes via sysfs and therefore depend 453on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make 454any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective 455code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not 456all drivers might be able to drop CONFIG_FB_DEVICE. 457 458Contact: Thomas Zimmermann <tzimmermann@suse.de> 459 460Level: Starter 461 462Clean up checks for already prepared/enabled in panels 463------------------------------------------------------ 464 465In a whole pile of panel drivers, we have code to make the 466prepare/unprepare/enable/disable callbacks behave as no-ops if they've already 467been called. To get some idea of the duplicated code, try:: 468 469 git grep 'if.*>prepared' -- drivers/gpu/drm/panel 470 git grep 'if.*>enabled' -- drivers/gpu/drm/panel 471 472In the patch ("drm/panel: Check for already prepared/enabled in drm_panel") 473we've moved this check to the core. Now we can most definitely remove the 474check from the individual panels and save a pile of code. 475 476In adition to removing the check from the individual panels, it is believed 477that even the core shouldn't need this check and that should be considered 478an error if other code ever relies on this check. The check in the core 479currently prints a warning whenever something is relying on this check with 480dev_warn(). After a little while, we likely want to promote this to a 481WARN(1) to help encourage folks not to rely on this behavior. 482 483Contact: Douglas Anderson <dianders@chromium.org> 484 485Level: Starter/Intermediate 486 487 488Core refactorings 489================= 490 491Make panic handling work 492------------------------ 493 494This is a really varied tasks with lots of little bits and pieces: 495 496* The panic path can't be tested currently, leading to constant breaking. The 497 main issue here is that panics can be triggered from hardirq contexts and 498 hence all panic related callback can run in hardirq context. It would be 499 awesome if we could test at least the fbdev helper code and driver code by 500 e.g. trigger calls through drm debugfs files. hardirq context could be 501 achieved by using an IPI to the local processor. 502 503* There's a massive confusion of different panic handlers. DRM fbdev emulation 504 helpers had their own (long removed), but on top of that the fbcon code itself 505 also has one. We need to make sure that they stop fighting over each other. 506 This is worked around by checking ``oops_in_progress`` at various entry points 507 into the DRM fbdev emulation helpers. A much cleaner approach here would be to 508 switch fbcon to the `threaded printk support 509 <https://lwn.net/Articles/800946/>`_. 510 511* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 512 isn't a full solution for panic paths. We need to make sure that it only 513 returns true if there's a panic going on for real, and fix up all the 514 fallout. 515 516* The panic handler must never sleep, which also means it can't ever 517 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 518 even spinlocks (because NMI and hardirq can panic too). We need to either 519 make sure to not call such paths, or trylock everything. Really tricky. 520 521* A clean solution would be an entirely separate panic output support in KMS, 522 bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling 523 <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_. 524 525* Encoding the actual oops and preceding dmesg in a QR might help with the 526 dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages 527 transfer using QR codes 528 <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_ 529 for some example code that could be reused. 530 531Contact: Daniel Vetter 532 533Level: Advanced 534 535Clean up the debugfs support 536---------------------------- 537 538There's a bunch of issues with it: 539 540- Convert drivers to support the drm_debugfs_add_files() function instead of 541 the drm_debugfs_create_files() function. 542 543- Improve late-register debugfs by rolling out the same debugfs pre-register 544 infrastructure for connector and crtc too. That way, the drivers won't need to 545 split their setup code into init and register anymore. 546 547- We probably want to have some support for debugfs files on crtc/connectors and 548 maybe other kms objects directly in core. There's even drm_print support in 549 the funcs for these objects to dump kms state, so it's all there. And then the 550 ->show() functions should obviously give you a pointer to the right object. 551 552- The drm_driver->debugfs_init hooks we have is just an artifact of the old 553 midlayered load sequence. DRM debugfs should work more like sysfs, where you 554 can create properties/files for an object anytime you want, and the core 555 takes care of publishing/unpuplishing all the files at register/unregister 556 time. Drivers shouldn't need to worry about these technicalities, and fixing 557 this (together with the drm_minor->drm_device move) would allow us to remove 558 debugfs_init. 559 560Contact: Daniel Vetter 561 562Level: Intermediate 563 564Object lifetime fixes 565--------------------- 566 567There's two related issues here 568 569- Cleanup up the various ->destroy callbacks, which often are all the same 570 simple code. 571 572- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, 573 which results in use-after free issues on driver unload. This can be serious 574 trouble even for drivers for hardware integrated on the SoC due to 575 EPROBE_DEFERRED backoff. 576 577Both these problems can be solved by switching over to drmm_kzalloc(), and the 578various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), 579drmm_universal_plane_alloc(), ... and so on. 580 581Contact: Daniel Vetter 582 583Level: Intermediate 584 585Remove automatic page mapping from dma-buf importing 586---------------------------------------------------- 587 588When importing dma-bufs, the dma-buf and PRIME frameworks automatically map 589imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and 590drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() 591even if they never do actual device DMA, but only CPU access through 592dma_buf_vmap(). This is a problem for USB devices, which do not support DMA 593operations. 594 595To fix the issue, automatic page mappings should be removed from the 596buffer-sharing code. Fixing this is a bit more involved, since the import/export 597cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over 598this problem for USB devices by fishing out the USB host controller device, as 599long as that supports DMA. Otherwise importing can still needlessly fail. 600 601Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 602 603Level: Advanced 604 605 606Better Testing 607============== 608 609Add unit tests using the Kernel Unit Testing (KUnit) framework 610-------------------------------------------------------------- 611 612The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ 613provides a common framework for unit tests within the Linux kernel. Having a 614test suite would allow to identify regressions earlier. 615 616A good candidate for the first unit tests are the format-conversion helpers in 617``drm_format_helper.c``. 618 619Contact: Javier Martinez Canillas <javierm@redhat.com> 620 621Level: Intermediate 622 623Enable trinity for DRM 624---------------------- 625 626And fix up the fallout. Should be really interesting ... 627 628Level: Advanced 629 630Make KMS tests in i-g-t generic 631------------------------------- 632 633The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 634including tons of testcases for corner-cases in the modesetting API. It would 635be awesome if those tests (at least the ones not relying on Intel-specific GEM 636features) could be made to run on any KMS driver. 637 638Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 639converting things over. For modeset tests we also first need a bit of 640infrastructure to use dumb buffers for untiled buffers, to be able to run all 641the non-i915 specific modeset tests. 642 643Level: Advanced 644 645Extend virtual test driver (VKMS) 646--------------------------------- 647 648See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 649internship task, since it only requires a virtual machine and can be sized to 650fit the available time. 651 652Level: See details 653 654Backlight Refactoring 655--------------------- 656 657Backlight drivers have a triple enable/disable state, which is a bit overkill. 658Plan to fix this: 659 6601. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 661 has started already. 6622. In all, only look at one of the three status bits set by the above helpers. 6633. Remove the other two status bits. 664 665Contact: Daniel Vetter 666 667Level: Intermediate 668 669Driver Specific 670=============== 671 672AMD DC Display Driver 673--------------------- 674 675AMD DC is the display driver for AMD devices starting with Vega. There has been 676a bunch of progress cleaning it up but there's still plenty of work to be done. 677 678See drivers/gpu/drm/amd/display/TODO for tasks. 679 680Contact: Harry Wentland, Alex Deucher 681 682Bootsplash 683========== 684 685There is support in place now for writing internal DRM clients making it 686possible to pick up the bootsplash work that was rejected because it was written 687for fbdev. 688 689- [v6,8/8] drm/client: Hack: Add bootsplash example 690 https://patchwork.freedesktop.org/patch/306579/ 691 692- [RFC PATCH v2 00/13] Kernel based bootsplash 693 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de 694 695Contact: Sam Ravnborg 696 697Level: Advanced 698 699Brightness handling on devices with multiple internal panels 700============================================================ 701 702On x86/ACPI devices there can be multiple backlight firmware interfaces: 703(ACPI) video, vendor specific and others. As well as direct/native (PWM) 704register programming by the KMS driver. 705 706To deal with this backlight drivers used on x86/ACPI call 707acpi_video_get_backlight_type() which has heuristics (+quirks) to select 708which backlight interface to use; and backlight drivers which do not match 709the returned type will not register themselves, so that only one backlight 710device gets registered (in a single GPU setup, see below). 711 712At the moment this more or less assumes that there will only 713be 1 (internal) panel on a system. 714 715On systems with 2 panels this may be a problem, depending on 716what interface acpi_video_get_backlight_type() selects: 717 7181. native: in this case the KMS driver is expected to know which backlight 719 device belongs to which output so everything should just work. 7202. video: this does support controlling multiple backlights, but some work 721 will need to be done to get the output <-> backlight device mapping 722 723The above assumes both panels will require the same backlight interface type. 724Things will break on systems with multiple panels where the 2 panels need 725a different type of control. E.g. one panel needs ACPI video backlight control, 726where as the other is using native backlight control. Currently in this case 727only one of the 2 required backlight devices will get registered, based on 728the acpi_video_get_backlight_type() return value. 729 730If this (theoretical) case ever shows up, then supporting this will need some 731work. A possible solution here would be to pass a device and connector-name 732to acpi_video_get_backlight_type() so that it can deal with this. 733 734Note in a way we already have a case where userspace sees 2 panels, 735in dual GPU laptop setups with a mux. On those systems we may see 736either 2 native backlight devices; or 2 native backlight devices. 737 738Userspace already has code to deal with this by detecting if the related 739panel is active (iow which way the mux between the GPU and the panels 740points) and then uses that backlight device. Userspace here very much 741assumes a single panel though. It picks only 1 of the 2 backlight devices 742and then only uses that one. 743 744Note that all userspace code (that I know off) is currently hardcoded 745to assume a single panel. 746 747Before the recent changes to not register multiple (e.g. video + native) 748/sys/class/backlight devices for a single panel (on a single GPU laptop), 749userspace would see multiple backlight devices all controlling the same 750backlight. 751 752To deal with this userspace had to always picks one preferred device under 753/sys/class/backlight and will ignore the others. So to support brightness 754control on multiple panels userspace will need to be updated too. 755 756There are plans to allow brightness control through the KMS API by adding 757a "display brightness" property to drm_connector objects for panels. This 758solves a number of issues with the /sys/class/backlight API, including not 759being able to map a sysfs backlight device to a specific connector. Any 760userspace changes to add support for brightness control on devices with 761multiple panels really should build on top of this new KMS property. 762 763Contact: Hans de Goede 764 765Level: Advanced 766 767Outside DRM 768=========== 769 770Convert fbdev drivers to DRM 771---------------------------- 772 773There are plenty of fbdev drivers for older hardware. Some hardware has 774become obsolete, but some still provides good(-enough) framebuffers. The 775drivers that are still useful should be converted to DRM and afterwards 776removed from fbdev. 777 778Very simple fbdev drivers can best be converted by starting with a new 779DRM driver. Simple KMS helpers and SHMEM should be able to handle any 780existing hardware. The new driver's call-back functions are filled from 781existing fbdev code. 782 783More complex fbdev drivers can be refactored step-by-step into a DRM 784driver with the help of the DRM fbconv helpers [4]_. These helpers provide 785the transition layer between the DRM core infrastructure and the fbdev 786driver interface. Create a new DRM driver on top of the fbconv helpers, 787copy over the fbdev driver, and hook it up to the DRM code. Examples for 788several fbdev drivers are available in Thomas Zimmermann's fbconv tree 789[4]_, as well as a tutorial of this process [5]_. The result is a primitive 790DRM driver that can run X11 and Weston. 791 792 .. [4] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 793 .. [5] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 794 795Contact: Thomas Zimmermann <tzimmermann@suse.de> 796 797Level: Advanced 798