1.. _todo: 2 3========= 4TODO list 5========= 6 7This section contains a list of smaller janitorial tasks in the kernel DRM 8graphics subsystem useful as newbie projects. Or for slow rainy days. 9 10Difficulty 11---------- 12 13To make it easier task are categorized into different levels: 14 15Starter: Good tasks to get started with the DRM subsystem. 16 17Intermediate: Tasks which need some experience with working in the DRM 18subsystem, or some specific GPU/display graphics knowledge. For debugging issue 19it's good to have the relevant hardware (or a virtual driver set up) available 20for testing. 21 22Advanced: Tricky tasks that need fairly good understanding of the DRM subsystem 23and graphics topics. Generally need the relevant hardware for development and 24testing. 25 26Subsystem-wide refactorings 27=========================== 28 29Remove custom dumb_map_offset implementations 30--------------------------------------------- 31 32All GEM based drivers should be using drm_gem_create_mmap_offset() instead. 33Audit each individual driver, make sure it'll work with the generic 34implementation (there's lots of outdated locking leftovers in various 35implementations), and then remove it. 36 37Contact: Daniel Vetter, respective driver maintainers 38 39Level: Intermediate 40 41Convert existing KMS drivers to atomic modesetting 42-------------------------------------------------- 43 443.19 has the atomic modeset interfaces and helpers, so drivers can now be 45converted over. Modern compositors like Wayland or Surfaceflinger on Android 46really want an atomic modeset interface, so this is all about the bright 47future. 48 49There is a conversion guide for atomic and all you need is a GPU for a 50non-converted driver (again virtual HW drivers for KVM are still all 51suitable). 52 53As part of this drivers also need to convert to universal plane (which means 54exposing primary & cursor as proper plane objects). But that's much easier to 55do by directly using the new atomic helper driver callbacks. 56 57Contact: Daniel Vetter, respective driver maintainers 58 59Level: Advanced 60 61Clean up the clipped coordination confusion around planes 62--------------------------------------------------------- 63 64We have a helper to get this right with drm_plane_helper_check_update(), but 65it's not consistently used. This should be fixed, preferrably in the atomic 66helpers (and drivers then moved over to clipped coordinates). Probably the 67helper should also be moved from drm_plane_helper.c to the atomic helpers, to 68avoid confusion - the other helpers in that file are all deprecated legacy 69helpers. 70 71Contact: Ville Syrjälä, Daniel Vetter, driver maintainers 72 73Level: Advanced 74 75Improve plane atomic_check helpers 76---------------------------------- 77 78Aside from the clipped coordinates right above there's a few suboptimal things 79with the current helpers: 80 81- drm_plane_helper_funcs->atomic_check gets called for enabled or disabled 82 planes. At best this seems to confuse drivers, worst it means they blow up 83 when the plane is disabled without the CRTC. The only special handling is 84 resetting values in the plane state structures, which instead should be moved 85 into the drm_plane_funcs->atomic_duplicate_state functions. 86 87- Once that's done, helpers could stop calling ->atomic_check for disabled 88 planes. 89 90- Then we could go through all the drivers and remove the more-or-less confused 91 checks for plane_state->fb and plane_state->crtc. 92 93Contact: Daniel Vetter 94 95Level: Advanced 96 97Convert early atomic drivers to async commit helpers 98---------------------------------------------------- 99 100For the first year the atomic modeset helpers didn't support asynchronous / 101nonblocking commits, and every driver had to hand-roll them. This is fixed 102now, but there's still a pile of existing drivers that easily could be 103converted over to the new infrastructure. 104 105One issue with the helpers is that they require that drivers handle completion 106events for atomic commits correctly. But fixing these bugs is good anyway. 107 108Contact: Daniel Vetter, respective driver maintainers 109 110Level: Advanced 111 112Fallout from atomic KMS 113----------------------- 114 115``drm_atomic_helper.c`` provides a batch of functions which implement legacy 116IOCTLs on top of the new atomic driver interface. Which is really nice for 117gradual conversion of drivers, but unfortunately the semantic mismatches are 118a bit too severe. So there's some follow-up work to adjust the function 119interfaces to fix these issues: 120 121* atomic needs the lock acquire context. At the moment that's passed around 122 implicitly with some horrible hacks, and it's also allocate with 123 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 124 the acquire context explicitly on stack and then also pass it down into 125 drivers explicitly so that the legacy-on-atomic functions can use them. 126 127 Except for some driver code this is done. This task should be finished by 128 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 129 130* A bunch of the vtable hooks are now in the wrong place: DRM has a split 131 between core vfunc tables (named ``drm_foo_funcs``), which are used to 132 implement the userspace ABI. And then there's the optional hooks for the 133 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 134 internal use. Some of these hooks should be move from ``_funcs`` to 135 ``_helper_funcs`` since they are not part of the core ABI. There's a 136 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 137 138Contact: Daniel Vetter 139 140Level: Intermediate 141 142Get rid of dev->struct_mutex from GEM drivers 143--------------------------------------------- 144 145``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 146everything. Nowadays in modern drivers the only bit where it's mandatory is 147serializing GEM buffer object destruction. Which unfortunately means drivers 148have to keep track of that lock and either call ``unreference`` or 149``unreference_locked`` depending upon context. 150 151Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 152and there's a ``gem_free_object_unlocked`` callback for any drivers which are 153entirely ``struct_mutex`` free. 154 155For drivers that need ``struct_mutex`` it should be replaced with a driver- 156private lock. The tricky part is the BO free functions, since those can't 157reliably take that lock any more. Instead state needs to be protected with 158suitable subordinate locks or some cleanup work pushed to a worker thread. For 159performance-critical drivers it might also be better to go with a more 160fine-grained per-buffer object and per-context lockings scheme. Currently only the 161``msm`` driver still use ``struct_mutex``. 162 163Contact: Daniel Vetter, respective driver maintainers 164 165Level: Advanced 166 167Convert logging to drm_* functions with drm_device paramater 168------------------------------------------------------------ 169 170For drivers which could have multiple instances, it is necessary to 171differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 172don't do this, drivers used dev_info/warn/err to make this differentiation. We 173now have drm_* variants of the drm print functions, so we can start to convert 174those drivers back to using drm-formatted specific log messages. 175 176Before you start this conversion please contact the relevant maintainers to make 177sure your work will be merged - not everyone agrees that the DRM dmesg macros 178are better. 179 180Contact: Sean Paul, Maintainer of the driver you plan to convert 181 182Level: Starter 183 184Convert drivers to use simple modeset suspend/resume 185---------------------------------------------------- 186 187Most drivers (except i915 and nouveau) that use 188drm_atomic_helper_suspend/resume() can probably be converted to use 189drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 190of the atomic suspend/resume code in older atomic modeset drivers. 191 192Contact: Maintainer of the driver you plan to convert 193 194Level: Intermediate 195 196Convert drivers to use drm_fbdev_generic_setup() 197------------------------------------------------ 198 199Most drivers can use drm_fbdev_generic_setup(). Driver have to implement 200atomic modesetting and GEM vmap support. Current generic fbdev emulation 201expects the framebuffer in system memory (or system-like memory). 202 203Contact: Maintainer of the driver you plan to convert 204 205Level: Intermediate 206 207drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 208----------------------------------------------------------------- 209 210A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 211Various hold-ups: 212 213- Need to switch over to the generic dirty tracking code using 214 drm_atomic_helper_dirtyfb first (e.g. qxl). 215 216- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 217 setup code can't be deleted. 218 219- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For 220 atomic drivers we could check for valid formats by calling 221 drm_plane_check_pixel_format() against all planes, and pass if any plane 222 supports the format. For non-atomic that's not possible since like the format 223 list for the primary plane is fake and we'd therefor reject valid formats. 224 225- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 226 version of the varios drm_gem_fb_create functions. Maybe called 227 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 228 229Contact: Daniel Vetter 230 231Level: Intermediate 232 233Clean up mmap forwarding 234------------------------ 235 236A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 237And also a lot of them forward dma-buf mmap to the gem mmap implementations. 238There's drm_gem_prime_mmap() for this now, but still needs to be rolled out. 239 240Contact: Daniel Vetter 241 242Level: Intermediate 243 244Generic fbdev defio support 245--------------------------- 246 247The defio support code in the fbdev core has some very specific requirements, 248which means drivers need to have a special framebuffer for fbdev. The main 249issue is that it uses some fields in struct page itself, which breaks shmem 250gem objects (and other things). To support defio, affected drivers require 251the use of a shadow buffer, which may add CPU and memory overhead. 252 253Possible solution would be to write our own defio mmap code in the drm fbdev 254emulation. It would need to fully wrap the existing mmap ops, forwarding 255everything after it has done the write-protect/mkwrite trickery: 256 257- In the drm_fbdev_fb_mmap helper, if we need defio, change the 258 default page prots to write-protected with something like this:: 259 260 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 261 262- Set the mkwrite and fsync callbacks with similar implementions to the core 263 fbdev defio stuff. These should all work on plain ptes, they don't actually 264 require a struct page. uff. These should all work on plain ptes, they don't 265 actually require a struct page. 266 267- Track the dirty pages in a separate structure (bitfield with one bit per page 268 should work) to avoid clobbering struct page. 269 270Might be good to also have some igt testcases for this. 271 272Contact: Daniel Vetter, Noralf Tronnes 273 274Level: Advanced 275 276idr_init_base() 277--------------- 278 279DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 280userspace IDs to internal objects, and in most places ID=0 means NULL and hence 281is never used. Switching to idr_init_base() for these would make the idr more 282efficient. 283 284Contact: Daniel Vetter 285 286Level: Starter 287 288struct drm_gem_object_funcs 289--------------------------- 290 291GEM objects can now have a function table instead of having the callbacks on the 292DRM driver struct. This is now the preferred way and drivers can be moved over. 293 294We also need a 2nd version of the CMA define that doesn't require the 295vmapping to be present (different hook for prime importing). Plus this needs to 296be rolled out to all drivers using their own implementations, too. 297 298Level: Intermediate 299 300Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 301--------------------------------------------------------- 302 303For cases where drivers are attempting to grab the modeset locks with a local 304acquire context. Replace the boilerplate code surrounding 305drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 306DRM_MODESET_LOCK_ALL_END() instead. 307 308This should also be done for all places where drm_modest_lock_all() is still 309used. 310 311As a reference, take a look at the conversions already completed in drm core. 312 313Contact: Sean Paul, respective driver maintainers 314 315Level: Starter 316 317Rename CMA helpers to DMA helpers 318--------------------------------- 319 320CMA (standing for contiguous memory allocator) is really a bit an accident of 321what these were used for first, a much better name would be DMA helpers. In the 322text these should even be called coherent DMA memory helpers (so maybe CDM, but 323no one knows what that means) since underneath they just use dma_alloc_coherent. 324 325Contact: Laurent Pinchart, Daniel Vetter 326 327Level: Intermediate (mostly because it is a huge tasks without good partial 328milestones, not technically itself that challenging) 329 330Convert direct mode.vrefresh accesses to use drm_mode_vrefresh() 331---------------------------------------------------------------- 332 333drm_display_mode.vrefresh isn't guaranteed to be populated. As such, using it 334is risky and has been known to cause div-by-zero bugs. Fortunately, drm core 335has helper which will use mode.vrefresh if it's !0 and will calculate it from 336the timings when it's 0. 337 338Use simple search/replace, or (more fun) cocci to replace instances of direct 339vrefresh access with a call to the helper. Check out 340https://lists.freedesktop.org/archives/dri-devel/2019-January/205186.html for 341inspiration. 342 343Once all instances of vrefresh have been converted, remove vrefresh from 344drm_display_mode to avoid future use. 345 346Contact: Sean Paul 347 348Level: Starter 349 350Remove drm_display_mode.hsync 351----------------------------- 352 353We have drm_mode_hsync() to calculate this from hsync_start/end, since drivers 354shouldn't/don't use this, remove this member to avoid any temptations to use it 355in the future. If there is any debug code using drm_display_mode.hsync, convert 356it to use drm_mode_hsync() instead. 357 358Contact: Sean Paul 359 360Level: Starter 361 362drm_fb_helper tasks 363------------------- 364 365- drm_fb_helper_restore_fbdev_mode_unlocked() should call restore_fbdev_mode() 366 not the _force variant so it can bail out if there is a master. But first 367 these igt tests need to be fixed: kms_fbcon_fbt@psr and 368 kms_fbcon_fbt@psr-suspend. 369 370- The max connector argument for drm_fb_helper_init() isn't used anymore and 371 can be removed. 372 373- The helper doesn't keep an array of connectors anymore so these can be 374 removed: drm_fb_helper_single_add_all_connectors(), 375 drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector(). 376 377Level: Intermediate 378 379connector register/unregister fixes 380----------------------------------- 381 382- For most connectors it's a no-op to call drm_connector_register/unregister 383 directly from driver code, drm_dev_register/unregister take care of this 384 already. We can remove all of them. 385 386- For dp drivers it's a bit more a mess, since we need the connector to be 387 registered when calling drm_dp_aux_register. Fix this by instead calling 388 drm_dp_aux_init, and moving the actual registering into a late_register 389 callback as recommended in the kerneldoc. 390 391Level: Intermediate 392 393Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 394--------------------------------------------------------------- 395 396The load/unload callbacks in struct &drm_driver are very much midlayers, plus 397for historical reasons they get the ordering wrong (and we can't fix that) 398between setting up the &drm_driver structure and calling drm_dev_register(). 399 400- Rework drivers to no longer use the load/unload callbacks, directly coding the 401 load/unload sequence into the driver's probe function. 402 403- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 404 callbacks for all modern drivers. 405 406Contact: Daniel Vetter 407 408Level: Intermediate 409 410Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 411--------------------------------------------------------------- 412 413Once EDID is parsed, the monitor HDMI support information is available through 414drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 415retrieve the same information, which is less efficient. 416 417Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 418drm_display_info.is_hdmi if applicable. 419 420Contact: Laurent Pinchart, respective driver maintainers 421 422Level: Intermediate 423 424Core refactorings 425================= 426 427Make panic handling work 428------------------------ 429 430This is a really varied tasks with lots of little bits and pieces: 431 432* The panic path can't be tested currently, leading to constant breaking. The 433 main issue here is that panics can be triggered from hardirq contexts and 434 hence all panic related callback can run in hardirq context. It would be 435 awesome if we could test at least the fbdev helper code and driver code by 436 e.g. trigger calls through drm debugfs files. hardirq context could be 437 achieved by using an IPI to the local processor. 438 439* There's a massive confusion of different panic handlers. DRM fbdev emulation 440 helpers have one, but on top of that the fbcon code itself also has one. We 441 need to make sure that they stop fighting over each another. 442 443* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 444 isn't a full solution for panic paths. We need to make sure that it only 445 returns true if there's a panic going on for real, and fix up all the 446 fallout. 447 448* The panic handler must never sleep, which also means it can't ever 449 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 450 even spinlocks (because NMI and hardirq can panic too). We need to either 451 make sure to not call such paths, or trylock everything. Really tricky. 452 453* For the above locking troubles reasons it's pretty much impossible to 454 attempt a synchronous modeset from panic handlers. The only thing we could 455 try to achive is an atomic ``set_base`` of the primary plane, and hope that 456 it shows up. Everything else probably needs to be delayed to some worker or 457 something else which happens later on. Otherwise it just kills the box 458 harder, prevent the panic from going out on e.g. netconsole. 459 460* There's also proposal for a simplied DRM console instead of the full-blown 461 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 462 obviously work for both console, in case we ever get kmslog merged. 463 464Contact: Daniel Vetter 465 466Level: Advanced 467 468Clean up the debugfs support 469---------------------------- 470 471There's a bunch of issues with it: 472 473- The drm_info_list ->show() function doesn't even bother to cast to the drm 474 structure for you. This is lazy. 475 476- We probably want to have some support for debugfs files on crtc/connectors and 477 maybe other kms objects directly in core. There's even drm_print support in 478 the funcs for these objects to dump kms state, so it's all there. And then the 479 ->show() functions should obviously give you a pointer to the right object. 480 481- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 482 anything we want to print drm_device (or maybe drm_file) is the right thing. 483 484- The drm_driver->debugfs_init hooks we have is just an artifact of the old 485 midlayered load sequence. DRM debugfs should work more like sysfs, where you 486 can create properties/files for an object anytime you want, and the core 487 takes care of publishing/unpuplishing all the files at register/unregister 488 time. Drivers shouldn't need to worry about these technicalities, and fixing 489 this (together with the drm_minor->drm_device move) would allow us to remove 490 debugfs_init. 491 492- Drop the return code and error checking from all debugfs functions. Greg KH is 493 working on this already. 494 495Contact: Daniel Vetter 496 497Level: Intermediate 498 499KMS cleanups 500------------ 501 502Some of these date from the very introduction of KMS in 2008 ... 503 504- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 505 function tables in drivers, but before we can remove them we need to make sure 506 that all the users in helpers and drivers do correctly check for a NULL 507 vtable. 508 509- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 510 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 511 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 512 historical reasons) misnamed drm_primary_helper_destroy() function. 513 514Level: Intermediate 515 516Better Testing 517============== 518 519Enable trinity for DRM 520---------------------- 521 522And fix up the fallout. Should be really interesting ... 523 524Level: Advanced 525 526Make KMS tests in i-g-t generic 527------------------------------- 528 529The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 530including tons of testcases for corner-cases in the modesetting API. It would 531be awesome if those tests (at least the ones not relying on Intel-specific GEM 532features) could be made to run on any KMS driver. 533 534Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 535converting things over. For modeset tests we also first need a bit of 536infrastructure to use dumb buffers for untiled buffers, to be able to run all 537the non-i915 specific modeset tests. 538 539Level: Advanced 540 541Extend virtual test driver (VKMS) 542--------------------------------- 543 544See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 545internship task, since it only requires a virtual machine and can be sized to 546fit the available time. 547 548Contact: Daniel Vetter 549 550Level: See details 551 552Backlight Refactoring 553--------------------- 554 555Backlight drivers have a triple enable/disable state, which is a bit overkill. 556Plan to fix this: 557 5581. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 559 has started already. 5602. In all, only look at one of the three status bits set by the above helpers. 5613. Remove the other two status bits. 562 563Contact: Daniel Vetter 564 565Level: Intermediate 566 567Driver Specific 568=============== 569 570AMD DC Display Driver 571--------------------- 572 573AMD DC is the display driver for AMD devices starting with Vega. There has been 574a bunch of progress cleaning it up but there's still plenty of work to be done. 575 576See drivers/gpu/drm/amd/display/TODO for tasks. 577 578Contact: Harry Wentland, Alex Deucher 579 580Bootsplash 581========== 582 583There is support in place now for writing internal DRM clients making it 584possible to pick up the bootsplash work that was rejected because it was written 585for fbdev. 586 587- [v6,8/8] drm/client: Hack: Add bootsplash example 588 https://patchwork.freedesktop.org/patch/306579/ 589 590- [RFC PATCH v2 00/13] Kernel based bootsplash 591 https://lkml.org/lkml/2017/12/13/764 592 593Contact: Sam Ravnborg 594 595Level: Advanced 596 597Outside DRM 598=========== 599 600Convert fbdev drivers to DRM 601---------------------------- 602 603There are plenty of fbdev drivers for older hardware. Some hwardware has 604become obsolete, but some still provides good(-enough) framebuffers. The 605drivers that are still useful should be converted to DRM and afterwards 606removed from fbdev. 607 608Very simple fbdev drivers can best be converted by starting with a new 609DRM driver. Simple KMS helpers and SHMEM should be able to handle any 610existing hardware. The new driver's call-back functions are filled from 611existing fbdev code. 612 613More complex fbdev drivers can be refactored step-by-step into a DRM 614driver with the help of the DRM fbconv helpers. [1] These helpers provide 615the transition layer between the DRM core infrastructure and the fbdev 616driver interface. Create a new DRM driver on top of the fbconv helpers, 617copy over the fbdev driver, and hook it up to the DRM code. Examples for 618several fbdev drivers are available at [1] and a tutorial of this process 619available at [2]. The result is a primitive DRM driver that can run X11 620and Weston. 621 622 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 623 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 624 625Contact: Thomas Zimmermann <tzimmermann@suse.de> 626 627Level: Advanced 628