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instead. 33Audit each individual driver, make sure it'll work with the generic 34implementation (there's lots of outdated locking leftovers in various 35implementations), and then remove it. 36 37Contact: Daniel Vetter, respective driver maintainers 38 39Level: Intermediate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 161the ``msm`` and `i915` drivers 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_modeset_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 330connector register/unregister fixes 331----------------------------------- 332 333- For most connectors it's a no-op to call drm_connector_register/unregister 334 directly from driver code, drm_dev_register/unregister take care of this 335 already. We can remove all of them. 336 337- For dp drivers it's a bit more a mess, since we need the connector to be 338 registered when calling drm_dp_aux_register. Fix this by instead calling 339 drm_dp_aux_init, and moving the actual registering into a late_register 340 callback as recommended in the kerneldoc. 341 342Level: Intermediate 343 344Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 345--------------------------------------------------------------- 346 347The load/unload callbacks in struct &drm_driver are very much midlayers, plus 348for historical reasons they get the ordering wrong (and we can't fix that) 349between setting up the &drm_driver structure and calling drm_dev_register(). 350 351- Rework drivers to no longer use the load/unload callbacks, directly coding the 352 load/unload sequence into the driver's probe function. 353 354- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 355 callbacks for all modern drivers. 356 357Contact: Daniel Vetter 358 359Level: Intermediate 360 361Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 362--------------------------------------------------------------- 363 364Once EDID is parsed, the monitor HDMI support information is available through 365drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 366retrieve the same information, which is less efficient. 367 368Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 369drm_display_info.is_hdmi if applicable. 370 371Contact: Laurent Pinchart, respective driver maintainers 372 373Level: Intermediate 374 375Consolidate custom driver modeset properties 376-------------------------------------------- 377 378Before atomic modeset took place, many drivers where creating their own 379properties. Among other things, atomic brought the requirement that custom, 380driver specific properties should not be used. 381 382For this task, we aim to introduce core helpers or reuse the existing ones 383if available: 384 385A quick, unconfirmed, examples list. 386 387Introduce core helpers: 388- audio (amdgpu, intel, gma500, radeon) 389- brightness, contrast, etc (armada, nouveau) - overlay only (?) 390- broadcast rgb (gma500, intel) 391- colorkey (armada, nouveau, rcar) - overlay only (?) 392- dither (amdgpu, nouveau, radeon) - varies across drivers 393- underscan family (amdgpu, radeon, nouveau) 394 395Already in core: 396- colorspace (sti) 397- tv format names, enhancements (gma500, intel) 398- tv overscan, margins, etc. (gma500, intel) 399- zorder (omapdrm) - same as zpos (?) 400 401 402Contact: Emil Velikov, respective driver maintainers 403 404Level: Intermediate 405 406Plumb drm_atomic_state all over 407------------------------------- 408 409Currently various atomic functions take just a single or a handful of 410object states (eg. plane state). While that single object state can 411suffice for some simple cases, we often have to dig out additional 412object states for dealing with various dependencies between the individual 413objects or the hardware they represent. The process of digging out the 414additional states is rather non-intuitive and error prone. 415 416To fix that most functions should rather take the overall 417drm_atomic_state as one of their parameters. The other parameters 418would generally be the object(s) we mainly want to interact with. 419 420For example, instead of 421 422.. code-block:: c 423 424 int (*atomic_check)(struct drm_plane *plane, struct drm_plane_state *state); 425 426we would have something like 427 428.. code-block:: c 429 430 int (*atomic_check)(struct drm_plane *plane, struct drm_atomic_state *state); 431 432The implementation can then trivially gain access to any required object 433state(s) via drm_atomic_get_plane_state(), drm_atomic_get_new_plane_state(), 434drm_atomic_get_old_plane_state(), and their equivalents for 435other object types. 436 437Additionally many drivers currently access the object->state pointer 438directly in their commit functions. That is not going to work if we 439eg. want to allow deeper commit pipelines as those pointers could 440then point to the states corresponding to a future commit instead of 441the current commit we're trying to process. Also non-blocking commits 442execute locklessly so there are serious concerns with dereferencing 443the object->state pointers without holding the locks that protect them. 444Use of drm_atomic_get_new_plane_state(), drm_atomic_get_old_plane_state(), 445etc. avoids these problems as well since they relate to a specific 446commit via the passed in drm_atomic_state. 447 448Contact: Ville Syrjälä, Daniel Vetter 449 450Level: Intermediate 451 452 453Core refactorings 454================= 455 456Make panic handling work 457------------------------ 458 459This is a really varied tasks with lots of little bits and pieces: 460 461* The panic path can't be tested currently, leading to constant breaking. The 462 main issue here is that panics can be triggered from hardirq contexts and 463 hence all panic related callback can run in hardirq context. It would be 464 awesome if we could test at least the fbdev helper code and driver code by 465 e.g. trigger calls through drm debugfs files. hardirq context could be 466 achieved by using an IPI to the local processor. 467 468* There's a massive confusion of different panic handlers. DRM fbdev emulation 469 helpers have one, but on top of that the fbcon code itself also has one. We 470 need to make sure that they stop fighting over each another. 471 472* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 473 isn't a full solution for panic paths. We need to make sure that it only 474 returns true if there's a panic going on for real, and fix up all the 475 fallout. 476 477* The panic handler must never sleep, which also means it can't ever 478 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 479 even spinlocks (because NMI and hardirq can panic too). We need to either 480 make sure to not call such paths, or trylock everything. Really tricky. 481 482* For the above locking troubles reasons it's pretty much impossible to 483 attempt a synchronous modeset from panic handlers. The only thing we could 484 try to achive is an atomic ``set_base`` of the primary plane, and hope that 485 it shows up. Everything else probably needs to be delayed to some worker or 486 something else which happens later on. Otherwise it just kills the box 487 harder, prevent the panic from going out on e.g. netconsole. 488 489* There's also proposal for a simplied DRM console instead of the full-blown 490 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 491 obviously work for both console, in case we ever get kmslog merged. 492 493Contact: Daniel Vetter 494 495Level: Advanced 496 497Clean up the debugfs support 498---------------------------- 499 500There's a bunch of issues with it: 501 502- The drm_info_list ->show() function doesn't even bother to cast to the drm 503 structure for you. This is lazy. 504 505- We probably want to have some support for debugfs files on crtc/connectors and 506 maybe other kms objects directly in core. There's even drm_print support in 507 the funcs for these objects to dump kms state, so it's all there. And then the 508 ->show() functions should obviously give you a pointer to the right object. 509 510- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 511 anything we want to print drm_device (or maybe drm_file) is the right thing. 512 513- The drm_driver->debugfs_init hooks we have is just an artifact of the old 514 midlayered load sequence. DRM debugfs should work more like sysfs, where you 515 can create properties/files for an object anytime you want, and the core 516 takes care of publishing/unpuplishing all the files at register/unregister 517 time. Drivers shouldn't need to worry about these technicalities, and fixing 518 this (together with the drm_minor->drm_device move) would allow us to remove 519 debugfs_init. 520 521- Drop the return code and error checking from all debugfs functions. Greg KH is 522 working on this already. 523 524Contact: Daniel Vetter 525 526Level: Intermediate 527 528KMS cleanups 529------------ 530 531Some of these date from the very introduction of KMS in 2008 ... 532 533- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 534 function tables in drivers, but before we can remove them we need to make sure 535 that all the users in helpers and drivers do correctly check for a NULL 536 vtable. 537 538- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 539 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 540 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 541 historical reasons) misnamed drm_primary_helper_destroy() function. 542 543Level: Intermediate 544 545Better Testing 546============== 547 548Enable trinity for DRM 549---------------------- 550 551And fix up the fallout. Should be really interesting ... 552 553Level: Advanced 554 555Make KMS tests in i-g-t generic 556------------------------------- 557 558The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 559including tons of testcases for corner-cases in the modesetting API. It would 560be awesome if those tests (at least the ones not relying on Intel-specific GEM 561features) could be made to run on any KMS driver. 562 563Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 564converting things over. For modeset tests we also first need a bit of 565infrastructure to use dumb buffers for untiled buffers, to be able to run all 566the non-i915 specific modeset tests. 567 568Level: Advanced 569 570Extend virtual test driver (VKMS) 571--------------------------------- 572 573See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 574internship task, since it only requires a virtual machine and can be sized to 575fit the available time. 576 577Contact: Daniel Vetter 578 579Level: See details 580 581Backlight Refactoring 582--------------------- 583 584Backlight drivers have a triple enable/disable state, which is a bit overkill. 585Plan to fix this: 586 5871. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 588 has started already. 5892. In all, only look at one of the three status bits set by the above helpers. 5903. Remove the other two status bits. 591 592Contact: Daniel Vetter 593 594Level: Intermediate 595 596Driver Specific 597=============== 598 599AMD DC Display Driver 600--------------------- 601 602AMD DC is the display driver for AMD devices starting with Vega. There has been 603a bunch of progress cleaning it up but there's still plenty of work to be done. 604 605See drivers/gpu/drm/amd/display/TODO for tasks. 606 607Contact: Harry Wentland, Alex Deucher 608 609Bootsplash 610========== 611 612There is support in place now for writing internal DRM clients making it 613possible to pick up the bootsplash work that was rejected because it was written 614for fbdev. 615 616- [v6,8/8] drm/client: Hack: Add bootsplash example 617 https://patchwork.freedesktop.org/patch/306579/ 618 619- [RFC PATCH v2 00/13] Kernel based bootsplash 620 https://lkml.org/lkml/2017/12/13/764 621 622Contact: Sam Ravnborg 623 624Level: Advanced 625 626Outside DRM 627=========== 628 629Convert fbdev drivers to DRM 630---------------------------- 631 632There are plenty of fbdev drivers for older hardware. Some hwardware has 633become obsolete, but some still provides good(-enough) framebuffers. The 634drivers that are still useful should be converted to DRM and afterwards 635removed from fbdev. 636 637Very simple fbdev drivers can best be converted by starting with a new 638DRM driver. Simple KMS helpers and SHMEM should be able to handle any 639existing hardware. The new driver's call-back functions are filled from 640existing fbdev code. 641 642More complex fbdev drivers can be refactored step-by-step into a DRM 643driver with the help of the DRM fbconv helpers. [1] These helpers provide 644the transition layer between the DRM core infrastructure and the fbdev 645driver interface. Create a new DRM driver on top of the fbconv helpers, 646copy over the fbdev driver, and hook it up to the DRM code. Examples for 647several fbdev drivers are available at [1] and a tutorial of this process 648available at [2]. The result is a primitive DRM driver that can run X11 649and Weston. 650 651 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 652 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 653 654Contact: Thomas Zimmermann <tzimmermann@suse.de> 655 656Level: Advanced 657