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instead. 33Audit each individual driver, make sure it'll work with the generic 34implementation (there's lots of outdated locking leftovers in various 35implementations), and then remove it. 36 37Contact: Daniel Vetter, respective driver maintainers 38 39Level: Intermediate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 75Convert early atomic drivers to async commit helpers 76---------------------------------------------------- 77 78For the first year the atomic modeset helpers didn't support asynchronous / 79nonblocking commits, and every driver had to hand-roll them. This is fixed 80now, but there's still a pile of existing drivers that easily could be 81converted over to the new infrastructure. 82 83One issue with the helpers is that they require that drivers handle completion 84events for atomic commits correctly. But fixing these bugs is good anyway. 85 86Contact: Daniel Vetter, respective driver maintainers 87 88Level: Advanced 89 90Fallout from atomic KMS 91----------------------- 92 93``drm_atomic_helper.c`` provides a batch of functions which implement legacy 94IOCTLs on top of the new atomic driver interface. Which is really nice for 95gradual conversion of drivers, but unfortunately the semantic mismatches are 96a bit too severe. So there's some follow-up work to adjust the function 97interfaces to fix these issues: 98 99* atomic needs the lock acquire context. At the moment that's passed around 100 implicitly with some horrible hacks, and it's also allocate with 101 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 102 the acquire context explicitly on stack and then also pass it down into 103 drivers explicitly so that the legacy-on-atomic functions can use them. 104 105 Except for some driver code this is done. This task should be finished by 106 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 107 108* A bunch of the vtable hooks are now in the wrong place: DRM has a split 109 between core vfunc tables (named ``drm_foo_funcs``), which are used to 110 implement the userspace ABI. And then there's the optional hooks for the 111 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 112 internal use. Some of these hooks should be move from ``_funcs`` to 113 ``_helper_funcs`` since they are not part of the core ABI. There's a 114 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 115 116Contact: Daniel Vetter 117 118Level: Intermediate 119 120Get rid of dev->struct_mutex from GEM drivers 121--------------------------------------------- 122 123``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 124everything. Nowadays in modern drivers the only bit where it's mandatory is 125serializing GEM buffer object destruction. Which unfortunately means drivers 126have to keep track of that lock and either call ``unreference`` or 127``unreference_locked`` depending upon context. 128 129Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 130and there's a ``gem_free_object_unlocked`` callback for any drivers which are 131entirely ``struct_mutex`` free. 132 133For drivers that need ``struct_mutex`` it should be replaced with a driver- 134private lock. The tricky part is the BO free functions, since those can't 135reliably take that lock any more. Instead state needs to be protected with 136suitable subordinate locks or some cleanup work pushed to a worker thread. For 137performance-critical drivers it might also be better to go with a more 138fine-grained per-buffer object and per-context lockings scheme. Currently only the 139``msm`` driver still use ``struct_mutex``. 140 141Contact: Daniel Vetter, respective driver maintainers 142 143Level: Advanced 144 145Convert logging to drm_* functions with drm_device paramater 146------------------------------------------------------------ 147 148For drivers which could have multiple instances, it is necessary to 149differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 150don't do this, drivers used dev_info/warn/err to make this differentiation. We 151now have drm_* variants of the drm print functions, so we can start to convert 152those drivers back to using drm-formatted specific log messages. 153 154Before you start this conversion please contact the relevant maintainers to make 155sure your work will be merged - not everyone agrees that the DRM dmesg macros 156are better. 157 158Contact: Sean Paul, Maintainer of the driver you plan to convert 159 160Level: Starter 161 162Convert drivers to use simple modeset suspend/resume 163---------------------------------------------------- 164 165Most drivers (except i915 and nouveau) that use 166drm_atomic_helper_suspend/resume() can probably be converted to use 167drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 168of the atomic suspend/resume code in older atomic modeset drivers. 169 170Contact: Maintainer of the driver you plan to convert 171 172Level: Intermediate 173 174Convert drivers to use drm_fbdev_generic_setup() 175------------------------------------------------ 176 177Most drivers can use drm_fbdev_generic_setup(). Driver have to implement 178atomic modesetting and GEM vmap support. Current generic fbdev emulation 179expects the framebuffer in system memory (or system-like memory). 180 181Contact: Maintainer of the driver you plan to convert 182 183Level: Intermediate 184 185drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 186----------------------------------------------------------------- 187 188A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 189Various hold-ups: 190 191- Need to switch over to the generic dirty tracking code using 192 drm_atomic_helper_dirtyfb first (e.g. qxl). 193 194- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 195 setup code can't be deleted. 196 197- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For 198 atomic drivers we could check for valid formats by calling 199 drm_plane_check_pixel_format() against all planes, and pass if any plane 200 supports the format. For non-atomic that's not possible since like the format 201 list for the primary plane is fake and we'd therefor reject valid formats. 202 203- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 204 version of the varios drm_gem_fb_create functions. Maybe called 205 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 206 207Contact: Daniel Vetter 208 209Level: Intermediate 210 211Clean up mmap forwarding 212------------------------ 213 214A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 215And also a lot of them forward dma-buf mmap to the gem mmap implementations. 216There's drm_gem_prime_mmap() for this now, but still needs to be rolled out. 217 218Contact: Daniel Vetter 219 220Level: Intermediate 221 222Generic fbdev defio support 223--------------------------- 224 225The defio support code in the fbdev core has some very specific requirements, 226which means drivers need to have a special framebuffer for fbdev. The main 227issue is that it uses some fields in struct page itself, which breaks shmem 228gem objects (and other things). To support defio, affected drivers require 229the use of a shadow buffer, which may add CPU and memory overhead. 230 231Possible solution would be to write our own defio mmap code in the drm fbdev 232emulation. It would need to fully wrap the existing mmap ops, forwarding 233everything after it has done the write-protect/mkwrite trickery: 234 235- In the drm_fbdev_fb_mmap helper, if we need defio, change the 236 default page prots to write-protected with something like this:: 237 238 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 239 240- Set the mkwrite and fsync callbacks with similar implementions to the core 241 fbdev defio stuff. These should all work on plain ptes, they don't actually 242 require a struct page. uff. These should all work on plain ptes, they don't 243 actually require a struct page. 244 245- Track the dirty pages in a separate structure (bitfield with one bit per page 246 should work) to avoid clobbering struct page. 247 248Might be good to also have some igt testcases for this. 249 250Contact: Daniel Vetter, Noralf Tronnes 251 252Level: Advanced 253 254idr_init_base() 255--------------- 256 257DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 258userspace IDs to internal objects, and in most places ID=0 means NULL and hence 259is never used. Switching to idr_init_base() for these would make the idr more 260efficient. 261 262Contact: Daniel Vetter 263 264Level: Starter 265 266struct drm_gem_object_funcs 267--------------------------- 268 269GEM objects can now have a function table instead of having the callbacks on the 270DRM driver struct. This is now the preferred way and drivers can be moved over. 271 272We also need a 2nd version of the CMA define that doesn't require the 273vmapping to be present (different hook for prime importing). Plus this needs to 274be rolled out to all drivers using their own implementations, too. 275 276Level: Intermediate 277 278Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 279--------------------------------------------------------- 280 281For cases where drivers are attempting to grab the modeset locks with a local 282acquire context. Replace the boilerplate code surrounding 283drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 284DRM_MODESET_LOCK_ALL_END() instead. 285 286This should also be done for all places where drm_modest_lock_all() is still 287used. 288 289As a reference, take a look at the conversions already completed in drm core. 290 291Contact: Sean Paul, respective driver maintainers 292 293Level: Starter 294 295Rename CMA helpers to DMA helpers 296--------------------------------- 297 298CMA (standing for contiguous memory allocator) is really a bit an accident of 299what these were used for first, a much better name would be DMA helpers. In the 300text these should even be called coherent DMA memory helpers (so maybe CDM, but 301no one knows what that means) since underneath they just use dma_alloc_coherent. 302 303Contact: Laurent Pinchart, Daniel Vetter 304 305Level: Intermediate (mostly because it is a huge tasks without good partial 306milestones, not technically itself that challenging) 307 308Convert direct mode.vrefresh accesses to use drm_mode_vrefresh() 309---------------------------------------------------------------- 310 311drm_display_mode.vrefresh isn't guaranteed to be populated. As such, using it 312is risky and has been known to cause div-by-zero bugs. Fortunately, drm core 313has helper which will use mode.vrefresh if it's !0 and will calculate it from 314the timings when it's 0. 315 316Use simple search/replace, or (more fun) cocci to replace instances of direct 317vrefresh access with a call to the helper. Check out 318https://lists.freedesktop.org/archives/dri-devel/2019-January/205186.html for 319inspiration. 320 321Once all instances of vrefresh have been converted, remove vrefresh from 322drm_display_mode to avoid future use. 323 324Contact: Sean Paul 325 326Level: Starter 327 328Remove drm_display_mode.hsync 329----------------------------- 330 331We have drm_mode_hsync() to calculate this from hsync_start/end, since drivers 332shouldn't/don't use this, remove this member to avoid any temptations to use it 333in the future. If there is any debug code using drm_display_mode.hsync, convert 334it to use drm_mode_hsync() instead. 335 336Contact: Sean Paul 337 338Level: Starter 339 340drm_fb_helper tasks 341------------------- 342 343- drm_fb_helper_restore_fbdev_mode_unlocked() should call restore_fbdev_mode() 344 not the _force variant so it can bail out if there is a master. But first 345 these igt tests need to be fixed: kms_fbcon_fbt@psr and 346 kms_fbcon_fbt@psr-suspend. 347 348- The max connector argument for drm_fb_helper_init() isn't used anymore and 349 can be removed. 350 351- The helper doesn't keep an array of connectors anymore so these can be 352 removed: drm_fb_helper_single_add_all_connectors(), 353 drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector(). 354 355Level: Intermediate 356 357connector register/unregister fixes 358----------------------------------- 359 360- For most connectors it's a no-op to call drm_connector_register/unregister 361 directly from driver code, drm_dev_register/unregister take care of this 362 already. We can remove all of them. 363 364- For dp drivers it's a bit more a mess, since we need the connector to be 365 registered when calling drm_dp_aux_register. Fix this by instead calling 366 drm_dp_aux_init, and moving the actual registering into a late_register 367 callback as recommended in the kerneldoc. 368 369Level: Intermediate 370 371Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 372--------------------------------------------------------------- 373 374The load/unload callbacks in struct &drm_driver are very much midlayers, plus 375for historical reasons they get the ordering wrong (and we can't fix that) 376between setting up the &drm_driver structure and calling drm_dev_register(). 377 378- Rework drivers to no longer use the load/unload callbacks, directly coding the 379 load/unload sequence into the driver's probe function. 380 381- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 382 callbacks for all modern drivers. 383 384Contact: Daniel Vetter 385 386Level: Intermediate 387 388Core refactorings 389================= 390 391Make panic handling work 392------------------------ 393 394This is a really varied tasks with lots of little bits and pieces: 395 396* The panic path can't be tested currently, leading to constant breaking. The 397 main issue here is that panics can be triggered from hardirq contexts and 398 hence all panic related callback can run in hardirq context. It would be 399 awesome if we could test at least the fbdev helper code and driver code by 400 e.g. trigger calls through drm debugfs files. hardirq context could be 401 achieved by using an IPI to the local processor. 402 403* There's a massive confusion of different panic handlers. DRM fbdev emulation 404 helpers have one, but on top of that the fbcon code itself also has one. We 405 need to make sure that they stop fighting over each another. 406 407* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 408 isn't a full solution for panic paths. We need to make sure that it only 409 returns true if there's a panic going on for real, and fix up all the 410 fallout. 411 412* The panic handler must never sleep, which also means it can't ever 413 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 414 even spinlocks (because NMI and hardirq can panic too). We need to either 415 make sure to not call such paths, or trylock everything. Really tricky. 416 417* For the above locking troubles reasons it's pretty much impossible to 418 attempt a synchronous modeset from panic handlers. The only thing we could 419 try to achive is an atomic ``set_base`` of the primary plane, and hope that 420 it shows up. Everything else probably needs to be delayed to some worker or 421 something else which happens later on. Otherwise it just kills the box 422 harder, prevent the panic from going out on e.g. netconsole. 423 424* There's also proposal for a simplied DRM console instead of the full-blown 425 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 426 obviously work for both console, in case we ever get kmslog merged. 427 428Contact: Daniel Vetter 429 430Level: Advanced 431 432Clean up the debugfs support 433---------------------------- 434 435There's a bunch of issues with it: 436 437- The drm_info_list ->show() function doesn't even bother to cast to the drm 438 structure for you. This is lazy. 439 440- We probably want to have some support for debugfs files on crtc/connectors and 441 maybe other kms objects directly in core. There's even drm_print support in 442 the funcs for these objects to dump kms state, so it's all there. And then the 443 ->show() functions should obviously give you a pointer to the right object. 444 445- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 446 anything we want to print drm_device (or maybe drm_file) is the right thing. 447 448- The drm_driver->debugfs_init hooks we have is just an artifact of the old 449 midlayered load sequence. DRM debugfs should work more like sysfs, where you 450 can create properties/files for an object anytime you want, and the core 451 takes care of publishing/unpuplishing all the files at register/unregister 452 time. Drivers shouldn't need to worry about these technicalities, and fixing 453 this (together with the drm_minor->drm_device move) would allow us to remove 454 debugfs_init. 455 456- Drop the return code and error checking from all debugfs functions. Greg KH is 457 working on this already. 458 459Contact: Daniel Vetter 460 461Level: Intermediate 462 463KMS cleanups 464------------ 465 466Some of these date from the very introduction of KMS in 2008 ... 467 468- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 469 function tables in drivers, but before we can remove them we need to make sure 470 that all the users in helpers and drivers do correctly check for a NULL 471 vtable. 472 473- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 474 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 475 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 476 historical reasons) misnamed drm_primary_helper_destroy() function. 477 478Level: Intermediate 479 480Better Testing 481============== 482 483Enable trinity for DRM 484---------------------- 485 486And fix up the fallout. Should be really interesting ... 487 488Level: Advanced 489 490Make KMS tests in i-g-t generic 491------------------------------- 492 493The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 494including tons of testcases for corner-cases in the modesetting API. It would 495be awesome if those tests (at least the ones not relying on Intel-specific GEM 496features) could be made to run on any KMS driver. 497 498Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 499converting things over. For modeset tests we also first need a bit of 500infrastructure to use dumb buffers for untiled buffers, to be able to run all 501the non-i915 specific modeset tests. 502 503Level: Advanced 504 505Extend virtual test driver (VKMS) 506--------------------------------- 507 508See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 509internship task, since it only requires a virtual machine and can be sized to 510fit the available time. 511 512Contact: Daniel Vetter 513 514Level: See details 515 516Backlight Refactoring 517--------------------- 518 519Backlight drivers have a triple enable/disable state, which is a bit overkill. 520Plan to fix this: 521 5221. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 523 has started already. 5242. In all, only look at one of the three status bits set by the above helpers. 5253. Remove the other two status bits. 526 527Contact: Daniel Vetter 528 529Level: Intermediate 530 531Driver Specific 532=============== 533 534AMD DC Display Driver 535--------------------- 536 537AMD DC is the display driver for AMD devices starting with Vega. There has been 538a bunch of progress cleaning it up but there's still plenty of work to be done. 539 540See drivers/gpu/drm/amd/display/TODO for tasks. 541 542Contact: Harry Wentland, Alex Deucher 543 544Bootsplash 545========== 546 547There is support in place now for writing internal DRM clients making it 548possible to pick up the bootsplash work that was rejected because it was written 549for fbdev. 550 551- [v6,8/8] drm/client: Hack: Add bootsplash example 552 https://patchwork.freedesktop.org/patch/306579/ 553 554- [RFC PATCH v2 00/13] Kernel based bootsplash 555 https://lkml.org/lkml/2017/12/13/764 556 557Contact: Sam Ravnborg 558 559Level: Advanced 560 561Outside DRM 562=========== 563 564Convert fbdev drivers to DRM 565---------------------------- 566 567There are plenty of fbdev drivers for older hardware. Some hwardware has 568become obsolete, but some still provides good(-enough) framebuffers. The 569drivers that are still useful should be converted to DRM and afterwards 570removed from fbdev. 571 572Very simple fbdev drivers can best be converted by starting with a new 573DRM driver. Simple KMS helpers and SHMEM should be able to handle any 574existing hardware. The new driver's call-back functions are filled from 575existing fbdev code. 576 577More complex fbdev drivers can be refactored step-by-step into a DRM 578driver with the help of the DRM fbconv helpers. [1] These helpers provide 579the transition layer between the DRM core infrastructure and the fbdev 580driver interface. Create a new DRM driver on top of the fbconv helpers, 581copy over the fbdev driver, and hook it up to the DRM code. Examples for 582several fbdev drivers are available at [1] and a tutorial of this process 583available at [2]. The result is a primitive DRM driver that can run X11 584and Weston. 585 586 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 587 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 588 589Contact: Thomas Zimmermann <tzimmermann@suse.de> 590 591Level: Advanced 592