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instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Simona Vetter, respective driver maintainers 41 42Level: Intermediate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: Simona 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, Simona 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: Simona 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: Simona 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: Simona 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: Simona 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 246Reimplement functions in drm_fbdev_fb_ops without fbdev 247------------------------------------------------------- 248 249A number of callback functions in drm_fbdev_fb_ops could benefit from 250being rewritten without dependencies on the fbdev module. Some of the 251helpers could further benefit from using struct iosys_map instead of 252raw pointers. 253 254Contact: Thomas Zimmermann <tzimmermann@suse.de>, Simona Vetter 255 256Level: Advanced 257 258Benchmark and optimize blitting and format-conversion function 259-------------------------------------------------------------- 260 261Drawing to display memory quickly is crucial for many applications' 262performance. 263 264On at least x86-64, sys_imageblit() is significantly slower than 265cfb_imageblit(), even though both use the same blitting algorithm and 266the latter is written for I/O memory. It turns out that cfb_imageblit() 267uses movl instructions, while sys_imageblit apparently does not. This 268seems to be a problem with gcc's optimizer. DRM's format-conversion 269helpers might be subject to similar issues. 270 271Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion 272helpers. In cases that can be further optimized, maybe implement a different 273algorithm. For micro-optimizations, use movl/movq instructions explicitly. 274That might possibly require architecture-specific helpers (e.g., storel() 275storeq()). 276 277Contact: Thomas Zimmermann <tzimmermann@suse.de> 278 279Level: Intermediate 280 281drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 282----------------------------------------------------------------- 283 284A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 285Various hold-ups: 286 287- Need to switch over to the generic dirty tracking code using 288 drm_atomic_helper_dirtyfb first (e.g. qxl). 289 290- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 291 setup code can't be deleted. 292 293- Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for 294 valid formats for atomic drivers. 295 296- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 297 version of the varios drm_gem_fb_create functions. Maybe called 298 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 299 300Contact: Simona Vetter 301 302Level: Intermediate 303 304Generic fbdev defio support 305--------------------------- 306 307The defio support code in the fbdev core has some very specific requirements, 308which means drivers need to have a special framebuffer for fbdev. The main 309issue is that it uses some fields in struct page itself, which breaks shmem 310gem objects (and other things). To support defio, affected drivers require 311the use of a shadow buffer, which may add CPU and memory overhead. 312 313Possible solution would be to write our own defio mmap code in the drm fbdev 314emulation. It would need to fully wrap the existing mmap ops, forwarding 315everything after it has done the write-protect/mkwrite trickery: 316 317- In the drm_fbdev_fb_mmap helper, if we need defio, change the 318 default page prots to write-protected with something like this:: 319 320 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 321 322- Set the mkwrite and fsync callbacks with similar implementions to the core 323 fbdev defio stuff. These should all work on plain ptes, they don't actually 324 require a struct page. uff. These should all work on plain ptes, they don't 325 actually require a struct page. 326 327- Track the dirty pages in a separate structure (bitfield with one bit per page 328 should work) to avoid clobbering struct page. 329 330Might be good to also have some igt testcases for this. 331 332Contact: Simona Vetter, Noralf Tronnes 333 334Level: Advanced 335 336connector register/unregister fixes 337----------------------------------- 338 339- For most connectors it's a no-op to call drm_connector_register/unregister 340 directly from driver code, drm_dev_register/unregister take care of this 341 already. We can remove all of them. 342 343- For dp drivers it's a bit more a mess, since we need the connector to be 344 registered when calling drm_dp_aux_register. Fix this by instead calling 345 drm_dp_aux_init, and moving the actual registering into a late_register 346 callback as recommended in the kerneldoc. 347 348Level: Intermediate 349 350Remove load/unload callbacks 351---------------------------- 352 353The load/unload callbacks in struct &drm_driver are very much midlayers, plus 354for historical reasons they get the ordering wrong (and we can't fix that) 355between setting up the &drm_driver structure and calling drm_dev_register(). 356 357- Rework drivers to no longer use the load/unload callbacks, directly coding the 358 load/unload sequence into the driver's probe function. 359 360- Once all drivers are converted, remove the load/unload callbacks. 361 362Contact: Simona Vetter 363 364Level: Intermediate 365 366Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 367--------------------------------------------------------------- 368 369Once EDID is parsed, the monitor HDMI support information is available through 370drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 371retrieve the same information, which is less efficient. 372 373Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 374drm_display_info.is_hdmi if applicable. 375 376Contact: Laurent Pinchart, respective driver maintainers 377 378Level: Intermediate 379 380Consolidate custom driver modeset properties 381-------------------------------------------- 382 383Before atomic modeset took place, many drivers where creating their own 384properties. Among other things, atomic brought the requirement that custom, 385driver specific properties should not be used. 386 387For this task, we aim to introduce core helpers or reuse the existing ones 388if available: 389 390A quick, unconfirmed, examples list. 391 392Introduce core helpers: 393- audio (amdgpu, intel, gma500, radeon) 394- brightness, contrast, etc (armada, nouveau) - overlay only (?) 395- broadcast rgb (gma500, intel) 396- colorkey (armada, nouveau, rcar) - overlay only (?) 397- dither (amdgpu, nouveau, radeon) - varies across drivers 398- underscan family (amdgpu, radeon, nouveau) 399 400Already in core: 401- colorspace (sti) 402- tv format names, enhancements (gma500, intel) 403- tv overscan, margins, etc. (gma500, intel) 404- zorder (omapdrm) - same as zpos (?) 405 406 407Contact: Emil Velikov, respective driver maintainers 408 409Level: Intermediate 410 411Use struct iosys_map throughout codebase 412---------------------------------------- 413 414Pointers to shared device memory are stored in struct iosys_map. Each 415instance knows whether it refers to system or I/O memory. Most of the DRM-wide 416interface have been converted to use struct iosys_map, but implementations 417often still use raw pointers. 418 419The task is to use struct iosys_map where it makes sense. 420 421* Memory managers should use struct iosys_map for dma-buf-imported buffers. 422* TTM might benefit from using struct iosys_map internally. 423* Framebuffer copying and blitting helpers should operate on struct iosys_map. 424 425Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Simona Vetter 426 427Level: Intermediate 428 429Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly 430-------------------------------------------------------------------------------------- 431 432The values in struct drm_mode_config.{max_width,max_height} describe the 433maximum supported framebuffer size. It's the virtual screen size, but many 434drivers treat it like limitations of the physical resolution. 435 436The maximum width depends on the hardware's maximum scanline pitch. The 437maximum height depends on the amount of addressable video memory. Review all 438drivers to initialize the fields to the correct values. 439 440Contact: Thomas Zimmermann <tzimmermann@suse.de> 441 442Level: Intermediate 443 444Request memory regions in all fbdev drivers 445-------------------------------------------- 446 447Old/ancient fbdev drivers do not request their memory properly. 448Go through these drivers and add code to request the memory regions 449that the driver uses. This requires adding calls to request_mem_region(), 450pci_request_region() or similar functions. Use helpers for managed cleanup 451where possible. Problematic areas include hardware that has exclusive ranges 452like VGA. VGA16fb does not request the range as it is expected. 453Drivers are pretty bad at doing this and there used to be conflicts among 454DRM and fbdev drivers. Still, it's the correct thing to do. 455 456Contact: Thomas Zimmermann <tzimmermann@suse.de> 457 458Level: Starter 459 460Remove driver dependencies on FB_DEVICE 461--------------------------------------- 462 463A number of fbdev drivers provide attributes via sysfs and therefore depend 464on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make 465any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective 466code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not 467all drivers might be able to drop CONFIG_FB_DEVICE. 468 469Contact: Thomas Zimmermann <tzimmermann@suse.de> 470 471Level: Starter 472 473Remove disable/unprepare in remove/shutdown in panel-simple and panel-edp 474------------------------------------------------------------------------- 475 476As of commit d2aacaf07395 ("drm/panel: Check for already prepared/enabled in 477drm_panel"), we have a check in the drm_panel core to make sure nobody 478double-calls prepare/enable/disable/unprepare. Eventually that should probably 479be turned into a WARN_ON() or somehow made louder. 480 481At the moment, we expect that we may still encounter the warnings in the 482drm_panel core when using panel-simple and panel-edp. Since those panel 483drivers are used with a lot of different DRM modeset drivers they still 484make an extra effort to disable/unprepare the panel themsevles at shutdown 485time. Specifically we could still encounter those warnings if the panel 486driver gets shutdown() _before_ the DRM modeset driver and the DRM modeset 487driver properly calls drm_atomic_helper_shutdown() in its own shutdown() 488callback. Warnings could be avoided in such a case by using something like 489device links to ensure that the panel gets shutdown() after the DRM modeset 490driver. 491 492Once all DRM modeset drivers are known to shutdown properly, the extra 493calls to disable/unprepare in remove/shutdown in panel-simple and panel-edp 494should be removed and this TODO item marked complete. 495 496Contact: Douglas Anderson <dianders@chromium.org> 497 498Level: Intermediate 499 500Transition away from using deprecated MIPI DSI functions 501-------------------------------------------------------- 502 503There are many functions defined in ``drm_mipi_dsi.c`` which have been 504deprecated. Each deprecated function was deprecated in favor of its `multi` 505variant (e.g. `mipi_dsi_generic_write()` and `mipi_dsi_generic_write_multi()`). 506The `multi` variant of a function includes improved error handling and logic 507which makes it more convenient to make several calls in a row, as most MIPI 508drivers do. 509 510Drivers should be updated to use undeprecated functions. Once all usages of the 511deprecated MIPI DSI functions have been removed, their definitions may be 512removed from ``drm_mipi_dsi.c``. 513 514Contact: Douglas Anderson <dianders@chromium.org> 515 516Level: Starter 517 518Remove devm_drm_put_bridge() 519---------------------------- 520 521Due to how the panel bridge handles the drm_bridge object lifetime, special 522care must be taken to dispose of the drm_bridge object when the 523panel_bridge is removed. This is currently managed using 524devm_drm_put_bridge(), but that is an unsafe, temporary workaround. To fix 525that, the DRM panel lifetime needs to be reworked. After the rework is 526done, remove devm_drm_put_bridge() and the TODO in 527drm_panel_bridge_remove(). 528 529Contact: Maxime Ripard <mripard@kernel.org>, 530 Luca Ceresoli <luca.ceresoli@bootlin.com> 531 532Level: Intermediate 533 534Core refactorings 535================= 536 537Make panic handling work 538------------------------ 539 540This is a really varied tasks with lots of little bits and pieces: 541 542* The panic path can't be tested currently, leading to constant breaking. The 543 main issue here is that panics can be triggered from hardirq contexts and 544 hence all panic related callback can run in hardirq context. It would be 545 awesome if we could test at least the fbdev helper code and driver code by 546 e.g. trigger calls through drm debugfs files. hardirq context could be 547 achieved by using an IPI to the local processor. 548 549* There's a massive confusion of different panic handlers. DRM fbdev emulation 550 helpers had their own (long removed), but on top of that the fbcon code itself 551 also has one. We need to make sure that they stop fighting over each other. 552 This is worked around by checking ``oops_in_progress`` at various entry points 553 into the DRM fbdev emulation helpers. A much cleaner approach here would be to 554 switch fbcon to the `threaded printk support 555 <https://lwn.net/Articles/800946/>`_. 556 557* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 558 isn't a full solution for panic paths. We need to make sure that it only 559 returns true if there's a panic going on for real, and fix up all the 560 fallout. 561 562* The panic handler must never sleep, which also means it can't ever 563 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 564 even spinlocks (because NMI and hardirq can panic too). We need to either 565 make sure to not call such paths, or trylock everything. Really tricky. 566 567* A clean solution would be an entirely separate panic output support in KMS, 568 bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling 569 <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_. 570 571* Encoding the actual oops and preceding dmesg in a QR might help with the 572 dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages 573 transfer using QR codes 574 <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_ 575 for some example code that could be reused. 576 577Contact: Simona Vetter 578 579Level: Advanced 580 581Clean up the debugfs support 582---------------------------- 583 584There's a bunch of issues with it: 585 586- Convert drivers to support the drm_debugfs_add_files() function instead of 587 the drm_debugfs_create_files() function. 588 589- Improve late-register debugfs by rolling out the same debugfs pre-register 590 infrastructure for connector and crtc too. That way, the drivers won't need to 591 split their setup code into init and register anymore. 592 593- We probably want to have some support for debugfs files on crtc/connectors and 594 maybe other kms objects directly in core. There's even drm_print support in 595 the funcs for these objects to dump kms state, so it's all there. And then the 596 ->show() functions should obviously give you a pointer to the right object. 597 598- The drm_driver->debugfs_init hooks we have is just an artifact of the old 599 midlayered load sequence. DRM debugfs should work more like sysfs, where you 600 can create properties/files for an object anytime you want, and the core 601 takes care of publishing/unpuplishing all the files at register/unregister 602 time. Drivers shouldn't need to worry about these technicalities, and fixing 603 this (together with the drm_minor->drm_device move) would allow us to remove 604 debugfs_init. 605 606Contact: Simona Vetter 607 608Level: Intermediate 609 610Object lifetime fixes 611--------------------- 612 613There's two related issues here 614 615- Cleanup up the various ->destroy callbacks, which often are all the same 616 simple code. 617 618- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, 619 which results in use-after free issues on driver unload. This can be serious 620 trouble even for drivers for hardware integrated on the SoC due to 621 EPROBE_DEFERRED backoff. 622 623Both these problems can be solved by switching over to drmm_kzalloc(), and the 624various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), 625drmm_universal_plane_alloc(), ... and so on. 626 627Contact: Simona Vetter 628 629Level: Intermediate 630 631Remove automatic page mapping from dma-buf importing 632---------------------------------------------------- 633 634When importing dma-bufs, the dma-buf and PRIME frameworks automatically map 635imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and 636drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() 637even if they never do actual device DMA, but only CPU access through 638dma_buf_vmap(). This is a problem for USB devices, which do not support DMA 639operations. 640 641To fix the issue, automatic page mappings should be removed from the 642buffer-sharing code. Fixing this is a bit more involved, since the import/export 643cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over 644this problem for USB devices by fishing out the USB host controller device, as 645long as that supports DMA. Otherwise importing can still needlessly fail. 646 647Contact: Thomas Zimmermann <tzimmermann@suse.de>, Simona Vetter 648 649Level: Advanced 650 651Implement a new DUMB_CREATE2 ioctl 652---------------------------------- 653 654The current DUMB_CREATE ioctl is not well defined. Instead of a pixel and 655framebuffer format, it only accepts a color mode of vague semantics. Assuming 656a linear framebuffer, the color mode gives an idea of the supported pixel 657format. But userspace effectively has to guess the correct values. It really 658only works reliably with framebuffers in XRGB8888. Userspace has begun to 659workaround these limitations by computing arbitrary format's buffer sizes and 660calculating their sizes in terms of XRGB8888 pixels. 661 662One possible solution is a new ioctl DUMB_CREATE2. It should accept a DRM 663format and a format modifier to resolve the color mode's ambiguity. As 664framebuffers can be multi-planar, the new ioctl has to return the buffer size, 665pitch and GEM handle for each individual color plane. 666 667In the first step, the new ioctl can be limited to the current features of 668the existing DUMB_CREATE. Individual drivers can then be extended to support 669multi-planar formats. Rockchip might require this and would be a good candidate. 670 671It might also be helpful to userspace to query information about the size of 672a potential buffer, if allocated. Userspace would supply geometry and format; 673the kernel would return minimal allocation sizes and scanline pitch. There is 674interest to allocate that memory from another device and provide it to the 675DRM driver (say via dma-buf). 676 677Another requested feature is the ability to allocate a buffer by size, without 678format. Accelators use this for their buffer allocation and it could likely be 679generalized. 680 681In addition to the kernel implementation, there must be user-space support 682for the new ioctl. There's code in Mesa that might be able to use the new 683call. 684 685Contact: Thomas Zimmermann <tzimmermann@suse.de> 686 687Level: Advanced 688 689Better Testing 690============== 691 692Add unit tests using the Kernel Unit Testing (KUnit) framework 693-------------------------------------------------------------- 694 695The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ 696provides a common framework for unit tests within the Linux kernel. Having a 697test suite would allow to identify regressions earlier. 698 699A good candidate for the first unit tests are the format-conversion helpers in 700``drm_format_helper.c``. 701 702Contact: Javier Martinez Canillas <javierm@redhat.com> 703 704Level: Intermediate 705 706Clean up and document former selftests suites 707--------------------------------------------- 708 709Some KUnit test suites (drm_buddy, drm_cmdline_parser, drm_damage_helper, 710drm_format, drm_framebuffer, drm_dp_mst_helper, drm_mm, drm_plane_helper and 711drm_rect) are former selftests suites that have been converted over when KUnit 712was first introduced. 713 714These suites were fairly undocumented, and with different goals than what unit 715tests can be. Trying to identify what each test in these suites actually test 716for, whether that makes sense for a unit test, and either remove it if it 717doesn't or document it if it does would be of great help. 718 719Contact: Maxime Ripard <mripard@kernel.org> 720 721Level: Intermediate 722 723Enable trinity for DRM 724---------------------- 725 726And fix up the fallout. Should be really interesting ... 727 728Level: Advanced 729 730Make KMS tests in i-g-t generic 731------------------------------- 732 733The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 734including tons of testcases for corner-cases in the modesetting API. It would 735be awesome if those tests (at least the ones not relying on Intel-specific GEM 736features) could be made to run on any KMS driver. 737 738Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 739converting things over. For modeset tests we also first need a bit of 740infrastructure to use dumb buffers for untiled buffers, to be able to run all 741the non-i915 specific modeset tests. 742 743Level: Advanced 744 745Extend virtual test driver (VKMS) 746--------------------------------- 747 748See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 749internship task, since it only requires a virtual machine and can be sized to 750fit the available time. 751 752Level: See details 753 754Backlight Refactoring 755--------------------- 756 757Backlight drivers have a triple enable/disable state, which is a bit overkill. 758Plan to fix this: 759 7601. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 761 has started already. 7622. In all, only look at one of the three status bits set by the above helpers. 7633. Remove the other two status bits. 764 765Contact: Simona Vetter 766 767Level: Intermediate 768 769Driver Specific 770=============== 771 772AMD DC Display Driver 773--------------------- 774 775AMD DC is the display driver for AMD devices starting with Vega. There has been 776a bunch of progress cleaning it up but there's still plenty of work to be done. 777 778See drivers/gpu/drm/amd/display/TODO for tasks. 779 780Contact: Harry Wentland, Alex Deucher 781 782Bootsplash 783========== 784 785There is support in place now for writing internal DRM clients making it 786possible to pick up the bootsplash work that was rejected because it was written 787for fbdev. 788 789- [v6,8/8] drm/client: Hack: Add bootsplash example 790 https://patchwork.freedesktop.org/patch/306579/ 791 792- [RFC PATCH v2 00/13] Kernel based bootsplash 793 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de 794 795Contact: Sam Ravnborg 796 797Level: Advanced 798 799Brightness handling on devices with multiple internal panels 800============================================================ 801 802On x86/ACPI devices there can be multiple backlight firmware interfaces: 803(ACPI) video, vendor specific and others. As well as direct/native (PWM) 804register programming by the KMS driver. 805 806To deal with this backlight drivers used on x86/ACPI call 807acpi_video_get_backlight_type() which has heuristics (+quirks) to select 808which backlight interface to use; and backlight drivers which do not match 809the returned type will not register themselves, so that only one backlight 810device gets registered (in a single GPU setup, see below). 811 812At the moment this more or less assumes that there will only 813be 1 (internal) panel on a system. 814 815On systems with 2 panels this may be a problem, depending on 816what interface acpi_video_get_backlight_type() selects: 817 8181. native: in this case the KMS driver is expected to know which backlight 819 device belongs to which output so everything should just work. 8202. video: this does support controlling multiple backlights, but some work 821 will need to be done to get the output <-> backlight device mapping 822 823The above assumes both panels will require the same backlight interface type. 824Things will break on systems with multiple panels where the 2 panels need 825a different type of control. E.g. one panel needs ACPI video backlight control, 826where as the other is using native backlight control. Currently in this case 827only one of the 2 required backlight devices will get registered, based on 828the acpi_video_get_backlight_type() return value. 829 830If this (theoretical) case ever shows up, then supporting this will need some 831work. A possible solution here would be to pass a device and connector-name 832to acpi_video_get_backlight_type() so that it can deal with this. 833 834Note in a way we already have a case where userspace sees 2 panels, 835in dual GPU laptop setups with a mux. On those systems we may see 836either 2 native backlight devices; or 2 native backlight devices. 837 838Userspace already has code to deal with this by detecting if the related 839panel is active (iow which way the mux between the GPU and the panels 840points) and then uses that backlight device. Userspace here very much 841assumes a single panel though. It picks only 1 of the 2 backlight devices 842and then only uses that one. 843 844Note that all userspace code (that I know off) is currently hardcoded 845to assume a single panel. 846 847Before the recent changes to not register multiple (e.g. video + native) 848/sys/class/backlight devices for a single panel (on a single GPU laptop), 849userspace would see multiple backlight devices all controlling the same 850backlight. 851 852To deal with this userspace had to always picks one preferred device under 853/sys/class/backlight and will ignore the others. So to support brightness 854control on multiple panels userspace will need to be updated too. 855 856There are plans to allow brightness control through the KMS API by adding 857a "display brightness" property to drm_connector objects for panels. This 858solves a number of issues with the /sys/class/backlight API, including not 859being able to map a sysfs backlight device to a specific connector. Any 860userspace changes to add support for brightness control on devices with 861multiple panels really should build on top of this new KMS property. 862 863Contact: Hans de Goede 864 865Level: Advanced 866 867Buffer age or other damage accumulation algorithm for buffer damage 868=================================================================== 869 870Drivers that do per-buffer uploads, need a buffer damage handling (rather than 871frame damage like drivers that do per-plane or per-CRTC uploads), but there is 872no support to get the buffer age or any other damage accumulation algorithm. 873 874For this reason, the damage helpers just fallback to a full plane update if the 875framebuffer attached to a plane has changed since the last page-flip. Drivers 876set &drm_plane_state.ignore_damage_clips to true as indication to 877drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next() 878helpers that the damage clips should be ignored. 879 880This should be improved to get damage tracking properly working on drivers that 881do per-buffer uploads. 882 883More information about damage tracking and references to learning materials can 884be found in :ref:`damage_tracking_properties`. 885 886Contact: Javier Martinez Canillas <javierm@redhat.com> 887 888Level: Advanced 889 890Querying errors from drm_syncobj 891================================ 892 893The drm_syncobj container can be used by driver independent code to signal 894complection of submission. 895 896One minor feature still missing is a generic DRM IOCTL to query the error 897status of binary and timeline drm_syncobj. 898 899This should probably be improved by implementing the necessary kernel interface 900and adding support for that in the userspace stack. 901 902Contact: Christian König 903 904Level: Starter 905 906Outside DRM 907=========== 908 909Convert fbdev drivers to DRM 910---------------------------- 911 912There are plenty of fbdev drivers for older hardware. Some hardware has 913become obsolete, but some still provides good(-enough) framebuffers. The 914drivers that are still useful should be converted to DRM and afterwards 915removed from fbdev. 916 917Very simple fbdev drivers can best be converted by starting with a new 918DRM driver. Simple KMS helpers and SHMEM should be able to handle any 919existing hardware. The new driver's call-back functions are filled from 920existing fbdev code. 921 922More complex fbdev drivers can be refactored step-by-step into a DRM 923driver with the help of the DRM fbconv helpers [4]_. These helpers provide 924the transition layer between the DRM core infrastructure and the fbdev 925driver interface. Create a new DRM driver on top of the fbconv helpers, 926copy over the fbdev driver, and hook it up to the DRM code. Examples for 927several fbdev drivers are available in Thomas Zimmermann's fbconv tree 928[4]_, as well as a tutorial of this process [5]_. The result is a primitive 929DRM driver that can run X11 and Weston. 930 931 .. [4] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 932 .. [5] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 933 934Contact: Thomas Zimmermann <tzimmermann@suse.de> 935 936Level: Advanced 937