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instead. 33Audit each individual driver, make sure it'll work with the generic 34implementation (there's lots of outdated locking leftovers in various 35implementations), and then remove it. 36 37Contact: Daniel Vetter, respective driver maintainers 38 39Level: Intermediate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 350connector register/unregister fixes 351----------------------------------- 352 353- For most connectors it's a no-op to call drm_connector_register/unregister 354 directly from driver code, drm_dev_register/unregister take care of this 355 already. We can remove all of them. 356 357- For dp drivers it's a bit more a mess, since we need the connector to be 358 registered when calling drm_dp_aux_register. Fix this by instead calling 359 drm_dp_aux_init, and moving the actual registering into a late_register 360 callback as recommended in the kerneldoc. 361 362Level: Intermediate 363 364Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 365--------------------------------------------------------------- 366 367The load/unload callbacks in struct &drm_driver are very much midlayers, plus 368for historical reasons they get the ordering wrong (and we can't fix that) 369between setting up the &drm_driver structure and calling drm_dev_register(). 370 371- Rework drivers to no longer use the load/unload callbacks, directly coding the 372 load/unload sequence into the driver's probe function. 373 374- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 375 callbacks for all modern drivers. 376 377Contact: Daniel Vetter 378 379Level: Intermediate 380 381Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 382--------------------------------------------------------------- 383 384Once EDID is parsed, the monitor HDMI support information is available through 385drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 386retrieve the same information, which is less efficient. 387 388Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 389drm_display_info.is_hdmi if applicable. 390 391Contact: Laurent Pinchart, respective driver maintainers 392 393Level: Intermediate 394 395Core refactorings 396================= 397 398Make panic handling work 399------------------------ 400 401This is a really varied tasks with lots of little bits and pieces: 402 403* The panic path can't be tested currently, leading to constant breaking. The 404 main issue here is that panics can be triggered from hardirq contexts and 405 hence all panic related callback can run in hardirq context. It would be 406 awesome if we could test at least the fbdev helper code and driver code by 407 e.g. trigger calls through drm debugfs files. hardirq context could be 408 achieved by using an IPI to the local processor. 409 410* There's a massive confusion of different panic handlers. DRM fbdev emulation 411 helpers have one, but on top of that the fbcon code itself also has one. We 412 need to make sure that they stop fighting over each another. 413 414* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 415 isn't a full solution for panic paths. We need to make sure that it only 416 returns true if there's a panic going on for real, and fix up all the 417 fallout. 418 419* The panic handler must never sleep, which also means it can't ever 420 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 421 even spinlocks (because NMI and hardirq can panic too). We need to either 422 make sure to not call such paths, or trylock everything. Really tricky. 423 424* For the above locking troubles reasons it's pretty much impossible to 425 attempt a synchronous modeset from panic handlers. The only thing we could 426 try to achive is an atomic ``set_base`` of the primary plane, and hope that 427 it shows up. Everything else probably needs to be delayed to some worker or 428 something else which happens later on. Otherwise it just kills the box 429 harder, prevent the panic from going out on e.g. netconsole. 430 431* There's also proposal for a simplied DRM console instead of the full-blown 432 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 433 obviously work for both console, in case we ever get kmslog merged. 434 435Contact: Daniel Vetter 436 437Level: Advanced 438 439Clean up the debugfs support 440---------------------------- 441 442There's a bunch of issues with it: 443 444- The drm_info_list ->show() function doesn't even bother to cast to the drm 445 structure for you. This is lazy. 446 447- We probably want to have some support for debugfs files on crtc/connectors and 448 maybe other kms objects directly in core. There's even drm_print support in 449 the funcs for these objects to dump kms state, so it's all there. And then the 450 ->show() functions should obviously give you a pointer to the right object. 451 452- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 453 anything we want to print drm_device (or maybe drm_file) is the right thing. 454 455- The drm_driver->debugfs_init hooks we have is just an artifact of the old 456 midlayered load sequence. DRM debugfs should work more like sysfs, where you 457 can create properties/files for an object anytime you want, and the core 458 takes care of publishing/unpuplishing all the files at register/unregister 459 time. Drivers shouldn't need to worry about these technicalities, and fixing 460 this (together with the drm_minor->drm_device move) would allow us to remove 461 debugfs_init. 462 463- Drop the return code and error checking from all debugfs functions. Greg KH is 464 working on this already. 465 466Contact: Daniel Vetter 467 468Level: Intermediate 469 470KMS cleanups 471------------ 472 473Some of these date from the very introduction of KMS in 2008 ... 474 475- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 476 function tables in drivers, but before we can remove them we need to make sure 477 that all the users in helpers and drivers do correctly check for a NULL 478 vtable. 479 480- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 481 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 482 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 483 historical reasons) misnamed drm_primary_helper_destroy() function. 484 485Level: Intermediate 486 487Better Testing 488============== 489 490Enable trinity for DRM 491---------------------- 492 493And fix up the fallout. Should be really interesting ... 494 495Level: Advanced 496 497Make KMS tests in i-g-t generic 498------------------------------- 499 500The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 501including tons of testcases for corner-cases in the modesetting API. It would 502be awesome if those tests (at least the ones not relying on Intel-specific GEM 503features) could be made to run on any KMS driver. 504 505Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 506converting things over. For modeset tests we also first need a bit of 507infrastructure to use dumb buffers for untiled buffers, to be able to run all 508the non-i915 specific modeset tests. 509 510Level: Advanced 511 512Extend virtual test driver (VKMS) 513--------------------------------- 514 515See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 516internship task, since it only requires a virtual machine and can be sized to 517fit the available time. 518 519Contact: Daniel Vetter 520 521Level: See details 522 523Backlight Refactoring 524--------------------- 525 526Backlight drivers have a triple enable/disable state, which is a bit overkill. 527Plan to fix this: 528 5291. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 530 has started already. 5312. In all, only look at one of the three status bits set by the above helpers. 5323. Remove the other two status bits. 533 534Contact: Daniel Vetter 535 536Level: Intermediate 537 538Driver Specific 539=============== 540 541AMD DC Display Driver 542--------------------- 543 544AMD DC is the display driver for AMD devices starting with Vega. There has been 545a bunch of progress cleaning it up but there's still plenty of work to be done. 546 547See drivers/gpu/drm/amd/display/TODO for tasks. 548 549Contact: Harry Wentland, Alex Deucher 550 551Bootsplash 552========== 553 554There is support in place now for writing internal DRM clients making it 555possible to pick up the bootsplash work that was rejected because it was written 556for fbdev. 557 558- [v6,8/8] drm/client: Hack: Add bootsplash example 559 https://patchwork.freedesktop.org/patch/306579/ 560 561- [RFC PATCH v2 00/13] Kernel based bootsplash 562 https://lkml.org/lkml/2017/12/13/764 563 564Contact: Sam Ravnborg 565 566Level: Advanced 567 568Outside DRM 569=========== 570 571Convert fbdev drivers to DRM 572---------------------------- 573 574There are plenty of fbdev drivers for older hardware. Some hwardware has 575become obsolete, but some still provides good(-enough) framebuffers. The 576drivers that are still useful should be converted to DRM and afterwards 577removed from fbdev. 578 579Very simple fbdev drivers can best be converted by starting with a new 580DRM driver. Simple KMS helpers and SHMEM should be able to handle any 581existing hardware. The new driver's call-back functions are filled from 582existing fbdev code. 583 584More complex fbdev drivers can be refactored step-by-step into a DRM 585driver with the help of the DRM fbconv helpers. [1] These helpers provide 586the transition layer between the DRM core infrastructure and the fbdev 587driver interface. Create a new DRM driver on top of the fbconv helpers, 588copy over the fbdev driver, and hook it up to the DRM code. Examples for 589several fbdev drivers are available at [1] and a tutorial of this process 590available at [2]. The result is a primitive DRM driver that can run X11 591and Weston. 592 593 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 594 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 595 596Contact: Thomas Zimmermann <tzimmermann@suse.de> 597 598Level: Advanced 599