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 10Subsystem-wide refactorings 11=========================== 12 13Remove custom dumb_map_offset implementations 14--------------------------------------------- 15 16All GEM based drivers should be using drm_gem_create_mmap_offset() instead. 17Audit each individual driver, make sure it'll work with the generic 18implementation (there's lots of outdated locking leftovers in various 19implementations), and then remove it. 20 21Contact: Daniel Vetter, respective driver maintainers 22 23Convert existing KMS drivers to atomic modesetting 24-------------------------------------------------- 25 263.19 has the atomic modeset interfaces and helpers, so drivers can now be 27converted over. Modern compositors like Wayland or Surfaceflinger on Android 28really want an atomic modeset interface, so this is all about the bright 29future. 30 31There is a conversion guide for atomic and all you need is a GPU for a 32non-converted driver (again virtual HW drivers for KVM are still all 33suitable). 34 35As part of this drivers also need to convert to universal plane (which means 36exposing primary & cursor as proper plane objects). But that's much easier to 37do by directly using the new atomic helper driver callbacks. 38 39Contact: Daniel Vetter, respective driver maintainers 40 41Clean up the clipped coordination confusion around planes 42--------------------------------------------------------- 43 44We have a helper to get this right with drm_plane_helper_check_update(), but 45it's not consistently used. This should be fixed, preferrably in the atomic 46helpers (and drivers then moved over to clipped coordinates). Probably the 47helper should also be moved from drm_plane_helper.c to the atomic helpers, to 48avoid confusion - the other helpers in that file are all deprecated legacy 49helpers. 50 51Contact: Ville Syrjälä, Daniel Vetter, driver maintainers 52 53Convert early atomic drivers to async commit helpers 54---------------------------------------------------- 55 56For the first year the atomic modeset helpers didn't support asynchronous / 57nonblocking commits, and every driver had to hand-roll them. This is fixed 58now, but there's still a pile of existing drivers that easily could be 59converted over to the new infrastructure. 60 61One issue with the helpers is that they require that drivers handle completion 62events for atomic commits correctly. But fixing these bugs is good anyway. 63 64Contact: Daniel Vetter, respective driver maintainers 65 66Fallout from atomic KMS 67----------------------- 68 69``drm_atomic_helper.c`` provides a batch of functions which implement legacy 70IOCTLs on top of the new atomic driver interface. Which is really nice for 71gradual conversion of drivers, but unfortunately the semantic mismatches are 72a bit too severe. So there's some follow-up work to adjust the function 73interfaces to fix these issues: 74 75* atomic needs the lock acquire context. At the moment that's passed around 76 implicitly with some horrible hacks, and it's also allocate with 77 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 78 the acquire context explicitly on stack and then also pass it down into 79 drivers explicitly so that the legacy-on-atomic functions can use them. 80 81 Except for some driver code this is done. This task should be finished by 82 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 83 84* A bunch of the vtable hooks are now in the wrong place: DRM has a split 85 between core vfunc tables (named ``drm_foo_funcs``), which are used to 86 implement the userspace ABI. And then there's the optional hooks for the 87 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 88 internal use. Some of these hooks should be move from ``_funcs`` to 89 ``_helper_funcs`` since they are not part of the core ABI. There's a 90 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 91 92Contact: Daniel Vetter 93 94Get rid of dev->struct_mutex from GEM drivers 95--------------------------------------------- 96 97``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 98everything. Nowadays in modern drivers the only bit where it's mandatory is 99serializing GEM buffer object destruction. Which unfortunately means drivers 100have to keep track of that lock and either call ``unreference`` or 101``unreference_locked`` depending upon context. 102 103Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 104and there's a ``gem_free_object_unlocked`` callback for any drivers which are 105entirely ``struct_mutex`` free. 106 107For drivers that need ``struct_mutex`` it should be replaced with a driver- 108private lock. The tricky part is the BO free functions, since those can't 109reliably take that lock any more. Instead state needs to be protected with 110suitable subordinate locks or some cleanup work pushed to a worker thread. For 111performance-critical drivers it might also be better to go with a more 112fine-grained per-buffer object and per-context lockings scheme. Currently only the 113``msm`` driver still use ``struct_mutex``. 114 115Contact: Daniel Vetter, respective driver maintainers 116 117Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent 118---------------------------------------------------------------------------- 119 120For drivers which could have multiple instances, it is necessary to 121differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 122don't do this, drivers used dev_info/warn/err to make this differentiation. We 123now have DRM_DEV_* variants of the drm print macros, so we can start to convert 124those drivers back to using drm-formwatted specific log messages. 125 126Before you start this conversion please contact the relevant maintainers to make 127sure your work will be merged - not everyone agrees that the DRM dmesg macros 128are better. 129 130Contact: Sean Paul, Maintainer of the driver you plan to convert 131 132Convert drivers to use simple modeset suspend/resume 133---------------------------------------------------- 134 135Most drivers (except i915 and nouveau) that use 136drm_atomic_helper_suspend/resume() can probably be converted to use 137drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 138of the atomic suspend/resume code in older atomic modeset drivers. 139 140Contact: Maintainer of the driver you plan to convert 141 142Convert drivers to use drm_fb_helper_fbdev_setup/teardown() 143----------------------------------------------------------- 144 145Most drivers can use drm_fb_helper_fbdev_setup() except maybe: 146 147- amdgpu which has special logic to decide whether to call 148 drm_helper_disable_unused_functions() 149 150- armada which isn't atomic and doesn't call 151 drm_helper_disable_unused_functions() 152 153- i915 which calls drm_fb_helper_initial_config() in a worker 154 155Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can 156probably use drm_fb_helper_fbdev_teardown(). 157 158Contact: Maintainer of the driver you plan to convert 159 160Clean up mmap forwarding 161------------------------ 162 163A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 164And also a lot of them forward dma-buf mmap to the gem mmap implementations. 165There's drm_gem_prime_mmap() for this now, but still needs to be rolled out. 166 167Contact: Daniel Vetter 168 169Generic fbdev defio support 170--------------------------- 171 172The defio support code in the fbdev core has some very specific requirements, 173which means drivers need to have a special framebuffer for fbdev. Which prevents 174us from using the generic fbdev emulation code everywhere. The main issue is 175that it uses some fields in struct page itself, which breaks shmem gem objects 176(and other things). 177 178Possible solution would be to write our own defio mmap code in the drm fbdev 179emulation. It would need to fully wrap the existing mmap ops, forwarding 180everything after it has done the write-protect/mkwrite trickery: 181 182- In the drm_fbdev_fb_mmap helper, if we need defio, change the 183 default page prots to write-protected with something like this:: 184 185 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 186 187- Set the mkwrite and fsync callbacks with similar implementions to the core 188 fbdev defio stuff. These should all work on plain ptes, they don't actually 189 require a struct page. uff. These should all work on plain ptes, they don't 190 actually require a struct page. 191 192- Track the dirty pages in a separate structure (bitfield with one bit per page 193 should work) to avoid clobbering struct page. 194 195Might be good to also have some igt testcases for this. 196 197Contact: Daniel Vetter, Noralf Tronnes 198 199Remove the ->gem_prime_res_obj callback 200-------------------------------------------- 201 202The ->gem_prime_res_obj callback can be removed from drivers by using the 203reservation_object in the drm_gem_object. It may also be possible to use the 204generic drm_gem_reservation_object_wait helper for waiting for a bo. 205 206Contact: Daniel Vetter 207 208idr_init_base() 209--------------- 210 211DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 212userspace IDs to internal objects, and in most places ID=0 means NULL and hence 213is never used. Switching to idr_init_base() for these would make the idr more 214efficient. 215 216Contact: Daniel Vetter 217 218struct drm_gem_object_funcs 219--------------------------- 220 221GEM objects can now have a function table instead of having the callbacks on the 222DRM driver struct. This is now the preferred way and drivers can be moved over. 223 224We also need a 2nd version of the CMA define that doesn't require the 225vmapping to be present (different hook for prime importing). Plus this needs to 226be rolled out to all drivers using their own implementations, too. 227 228Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 229--------------------------------------------------------- 230 231For cases where drivers are attempting to grab the modeset locks with a local 232acquire context. Replace the boilerplate code surrounding 233drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 234DRM_MODESET_LOCK_ALL_END() instead. 235 236This should also be done for all places where drm_modest_lock_all() is still 237used. 238 239As a reference, take a look at the conversions already completed in drm core. 240 241Contact: Sean Paul, respective driver maintainers 242 243Rename CMA helpers to DMA helpers 244--------------------------------- 245 246CMA (standing for contiguous memory allocator) is really a bit an accident of 247what these were used for first, a much better name would be DMA helpers. In the 248text these should even be called coherent DMA memory helpers (so maybe CDM, but 249no one knows what that means) since underneath they just use dma_alloc_coherent. 250 251Contact: Laurent Pinchart, Daniel Vetter 252 253Convert direct mode.vrefresh accesses to use drm_mode_vrefresh() 254---------------------------------------------------------------- 255 256drm_display_mode.vrefresh isn't guaranteed to be populated. As such, using it 257is risky and has been known to cause div-by-zero bugs. Fortunately, drm core 258has helper which will use mode.vrefresh if it's !0 and will calculate it from 259the timings when it's 0. 260 261Use simple search/replace, or (more fun) cocci to replace instances of direct 262vrefresh access with a call to the helper. Check out 263https://lists.freedesktop.org/archives/dri-devel/2019-January/205186.html for 264inspiration. 265 266Once all instances of vrefresh have been converted, remove vrefresh from 267drm_display_mode to avoid future use. 268 269Contact: Sean Paul 270 271Remove drm_display_mode.hsync 272----------------------------- 273 274We have drm_mode_hsync() to calculate this from hsync_start/end, since drivers 275shouldn't/don't use this, remove this member to avoid any temptations to use it 276in the future. If there is any debug code using drm_display_mode.hsync, convert 277it to use drm_mode_hsync() instead. 278 279Contact: Sean Paul 280 281drm_fb_helper tasks 282------------------- 283 284- drm_fb_helper_restore_fbdev_mode_unlocked() should call restore_fbdev_mode() 285 not the _force variant so it can bail out if there is a master. But first 286 these igt tests need to be fixed: kms_fbcon_fbt@psr and 287 kms_fbcon_fbt@psr-suspend. 288 289- The max connector argument for drm_fb_helper_init() and 290 drm_fb_helper_fbdev_setup() isn't used anymore and can be removed. 291 292- The helper doesn't keep an array of connectors anymore so these can be 293 removed: drm_fb_helper_single_add_all_connectors(), 294 drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector(). 295 296Core refactorings 297================= 298 299Clean up the DRM header mess 300---------------------------- 301 302The DRM subsystem originally had only one huge global header, ``drmP.h``. This 303is now split up, but many source files still include it. The remaining part of 304the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the 305headers needed (and fixing up any missing pre-declarations in the headers). 306 307In the end no .c file should need to include ``drmP.h`` anymore. 308 309Contact: Daniel Vetter 310 311Make panic handling work 312------------------------ 313 314This is a really varied tasks with lots of little bits and pieces: 315 316* The panic path can't be tested currently, leading to constant breaking. The 317 main issue here is that panics can be triggered from hardirq contexts and 318 hence all panic related callback can run in hardirq context. It would be 319 awesome if we could test at least the fbdev helper code and driver code by 320 e.g. trigger calls through drm debugfs files. hardirq context could be 321 achieved by using an IPI to the local processor. 322 323* There's a massive confusion of different panic handlers. DRM fbdev emulation 324 helpers have one, but on top of that the fbcon code itself also has one. We 325 need to make sure that they stop fighting over each another. 326 327* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 328 isn't a full solution for panic paths. We need to make sure that it only 329 returns true if there's a panic going on for real, and fix up all the 330 fallout. 331 332* The panic handler must never sleep, which also means it can't ever 333 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 334 even spinlocks (because NMI and hardirq can panic too). We need to either 335 make sure to not call such paths, or trylock everything. Really tricky. 336 337* For the above locking troubles reasons it's pretty much impossible to 338 attempt a synchronous modeset from panic handlers. The only thing we could 339 try to achive is an atomic ``set_base`` of the primary plane, and hope that 340 it shows up. Everything else probably needs to be delayed to some worker or 341 something else which happens later on. Otherwise it just kills the box 342 harder, prevent the panic from going out on e.g. netconsole. 343 344* There's also proposal for a simplied DRM console instead of the full-blown 345 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 346 obviously work for both console, in case we ever get kmslog merged. 347 348Contact: Daniel Vetter 349 350Clean up the debugfs support 351---------------------------- 352 353There's a bunch of issues with it: 354 355- The drm_info_list ->show() function doesn't even bother to cast to the drm 356 structure for you. This is lazy. 357 358- We probably want to have some support for debugfs files on crtc/connectors and 359 maybe other kms objects directly in core. There's even drm_print support in 360 the funcs for these objects to dump kms state, so it's all there. And then the 361 ->show() functions should obviously give you a pointer to the right object. 362 363- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 364 anything we want to print drm_device (or maybe drm_file) is the right thing. 365 366- The drm_driver->debugfs_init hooks we have is just an artifact of the old 367 midlayered load sequence. DRM debugfs should work more like sysfs, where you 368 can create properties/files for an object anytime you want, and the core 369 takes care of publishing/unpuplishing all the files at register/unregister 370 time. Drivers shouldn't need to worry about these technicalities, and fixing 371 this (together with the drm_minor->drm_device move) would allow us to remove 372 debugfs_init. 373 374- Drop the return code and error checking from all debugfs functions. Greg KH is 375 working on this already. 376 377Contact: Daniel Vetter 378 379KMS cleanups 380------------ 381 382Some of these date from the very introduction of KMS in 2008 ... 383 384- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 385 function tables in drivers, but before we can remove them we need to make sure 386 that all the users in helpers and drivers do correctly check for a NULL 387 vtable. 388 389- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 390 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 391 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 392 historical reasons) misnamed drm_primary_helper_destroy() function. 393 394Better Testing 395============== 396 397Enable trinity for DRM 398---------------------- 399 400And fix up the fallout. Should be really interesting ... 401 402Make KMS tests in i-g-t generic 403------------------------------- 404 405The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 406including tons of testcases for corner-cases in the modesetting API. It would 407be awesome if those tests (at least the ones not relying on Intel-specific GEM 408features) could be made to run on any KMS driver. 409 410Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 411converting things over. For modeset tests we also first need a bit of 412infrastructure to use dumb buffers for untiled buffers, to be able to run all 413the non-i915 specific modeset tests. 414 415Extend virtual test driver (VKMS) 416--------------------------------- 417 418See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 419internship task, since it only requires a virtual machine and can be sized to 420fit the available time. 421 422Contact: Daniel Vetter 423 424Backlight Refactoring 425--------------------- 426 427Backlight drivers have a triple enable/disable state, which is a bit overkill. 428Plan to fix this: 429 4301. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 431 has started already. 4322. In all, only look at one of the three status bits set by the above helpers. 4333. Remove the other two status bits. 434 435Contact: Daniel Vetter 436 437Driver Specific 438=============== 439 440AMD DC Display Driver 441--------------------- 442 443AMD DC is the display driver for AMD devices starting with Vega. There has been 444a bunch of progress cleaning it up but there's still plenty of work to be done. 445 446See drivers/gpu/drm/amd/display/TODO for tasks. 447 448Contact: Harry Wentland, Alex Deucher 449 450i915 451---- 452 453- Our early/late pm callbacks could be removed in favour of using 454 device_link_add to model the dependency between i915 and snd_had. See 455 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html 456 457Bootsplash 458========== 459 460There is support in place now for writing internal DRM clients making it 461possible to pick up the bootsplash work that was rejected because it was written 462for fbdev. 463 464- [v6,8/8] drm/client: Hack: Add bootsplash example 465 https://patchwork.freedesktop.org/patch/306579/ 466 467- [RFC PATCH v2 00/13] Kernel based bootsplash 468 https://lkml.org/lkml/2017/12/13/764 469 470Contact: Sam Ravnborg 471 472Outside DRM 473=========== 474