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 13De-midlayer drivers 14------------------- 15 16With the recent ``drm_bus`` cleanup patches for 3.17 it is no longer required 17to have a ``drm_bus`` structure set up. Drivers can directly set up the 18``drm_device`` structure instead of relying on bus methods in ``drm_usb.c`` 19and ``drm_pci.c``. The goal is to get rid of the driver's ``->load`` / 20``->unload`` callbacks and open-code the load/unload sequence properly, using 21the new two-stage ``drm_device`` setup/teardown. 22 23Once all existing drivers are converted we can also remove those bus support 24files for USB and platform devices. 25 26All you need is a GPU for a non-converted driver (currently almost all of 27them, but also all the virtual ones used by KVM, so everyone qualifies). 28 29Contact: Daniel Vetter, Thierry Reding, respective driver maintainers 30 31 32Remove custom dumb_map_offset implementations 33--------------------------------------------- 34 35All GEM based drivers should be using drm_gem_create_mmap_offset() instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Convert existing KMS drivers to atomic modesetting 43-------------------------------------------------- 44 453.19 has the atomic modeset interfaces and helpers, so drivers can now be 46converted over. Modern compositors like Wayland or Surfaceflinger on Android 47really want an atomic modeset interface, so this is all about the bright 48future. 49 50There is a conversion guide for atomic and all you need is a GPU for a 51non-converted driver (again virtual HW drivers for KVM are still all 52suitable). 53 54As part of this drivers also need to convert to universal plane (which means 55exposing primary & cursor as proper plane objects). But that's much easier to 56do by directly using the new atomic helper driver callbacks. 57 58Contact: Daniel Vetter, respective driver maintainers 59 60Clean up the clipped coordination confusion around planes 61--------------------------------------------------------- 62 63We have a helper to get this right with drm_plane_helper_check_update(), but 64it's not consistently used. This should be fixed, preferrably in the atomic 65helpers (and drivers then moved over to clipped coordinates). Probably the 66helper should also be moved from drm_plane_helper.c to the atomic helpers, to 67avoid confusion - the other helpers in that file are all deprecated legacy 68helpers. 69 70Contact: Ville Syrjälä, Daniel Vetter, driver maintainers 71 72Convert early atomic drivers to async commit helpers 73---------------------------------------------------- 74 75For the first year the atomic modeset helpers didn't support asynchronous / 76nonblocking commits, and every driver had to hand-roll them. This is fixed 77now, but there's still a pile of existing drivers that easily could be 78converted over to the new infrastructure. 79 80One issue with the helpers is that they require that drivers handle completion 81events for atomic commits correctly. But fixing these bugs is good anyway. 82 83Contact: Daniel Vetter, respective driver maintainers 84 85Better manual-upload support for atomic 86--------------------------------------- 87 88This would be especially useful for tinydrm: 89 90- Add a struct drm_rect dirty_clip to drm_crtc_state. When duplicating the 91 crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in 92 __drm_atomic_helper_crtc_duplicate_state(). 93 94- Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_ 95 prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this 96 is a function useful to implement the fb->dirty function. 97 98- Create a new drm_fb_dirty function which does essentially what e.g. 99 mipi_dbi_fb_dirty does. You can use e.g. drm_atomic_helper_update_plane as the 100 template. But instead of doing a simple full-screen plane update, this new 101 helper also sets crtc_state->dirty_clip to the right coordinates. And of 102 course it needs to check whether the fb is actually active (and maybe where), 103 so there's some book-keeping involved. There's also some good fun involved in 104 scaling things appropriately. For that case we might simply give up and 105 declare the entire area covered by the plane as dirty. 106 107Contact: Noralf Trønnes, Daniel Vetter 108 109Fallout from atomic KMS 110----------------------- 111 112``drm_atomic_helper.c`` provides a batch of functions which implement legacy 113IOCTLs on top of the new atomic driver interface. Which is really nice for 114gradual conversion of drivers, but unfortunately the semantic mismatches are 115a bit too severe. So there's some follow-up work to adjust the function 116interfaces to fix these issues: 117 118* atomic needs the lock acquire context. At the moment that's passed around 119 implicitly with some horrible hacks, and it's also allocate with 120 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 121 the acquire context explicitly on stack and then also pass it down into 122 drivers explicitly so that the legacy-on-atomic functions can use them. 123 124 Except for some driver code this is done. This task should be finished by 125 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 126 127* A bunch of the vtable hooks are now in the wrong place: DRM has a split 128 between core vfunc tables (named ``drm_foo_funcs``), which are used to 129 implement the userspace ABI. And then there's the optional hooks for the 130 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 131 internal use. Some of these hooks should be move from ``_funcs`` to 132 ``_helper_funcs`` since they are not part of the core ABI. There's a 133 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 134 135Contact: Daniel Vetter 136 137Get rid of dev->struct_mutex from GEM drivers 138--------------------------------------------- 139 140``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 141everything. Nowadays in modern drivers the only bit where it's mandatory is 142serializing GEM buffer object destruction. Which unfortunately means drivers 143have to keep track of that lock and either call ``unreference`` or 144``unreference_locked`` depending upon context. 145 146Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 147and there's a ``gem_free_object_unlocked`` callback for any drivers which are 148entirely ``struct_mutex`` free. 149 150For drivers that need ``struct_mutex`` it should be replaced with a driver- 151private lock. The tricky part is the BO free functions, since those can't 152reliably take that lock any more. Instead state needs to be protected with 153suitable subordinate locks or some cleanup work pushed to a worker thread. For 154performance-critical drivers it might also be better to go with a more 155fine-grained per-buffer object and per-context lockings scheme. Currently only the 156``msm`` driver still use ``struct_mutex``. 157 158Contact: Daniel Vetter, respective driver maintainers 159 160Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent 161---------------------------------------------------------------------------- 162 163For drivers which could have multiple instances, it is necessary to 164differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 165don't do this, drivers used dev_info/warn/err to make this differentiation. We 166now have DRM_DEV_* variants of the drm print macros, so we can start to convert 167those drivers back to using drm-formwatted specific log messages. 168 169Before you start this conversion please contact the relevant maintainers to make 170sure your work will be merged - not everyone agrees that the DRM dmesg macros 171are better. 172 173Contact: Sean Paul, Maintainer of the driver you plan to convert 174 175Convert drivers to use simple modeset suspend/resume 176---------------------------------------------------- 177 178Most drivers (except i915 and nouveau) that use 179drm_atomic_helper_suspend/resume() can probably be converted to use 180drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 181of the atomic suspend/resume code in older atomic modeset drivers. 182 183Contact: Maintainer of the driver you plan to convert 184 185Convert drivers to use drm_fb_helper_fbdev_setup/teardown() 186----------------------------------------------------------- 187 188Most drivers can use drm_fb_helper_fbdev_setup() except maybe: 189 190- amdgpu which has special logic to decide whether to call 191 drm_helper_disable_unused_functions() 192 193- armada which isn't atomic and doesn't call 194 drm_helper_disable_unused_functions() 195 196- i915 which calls drm_fb_helper_initial_config() in a worker 197 198Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can 199probably use drm_fb_helper_fbdev_teardown(). 200 201Contact: Maintainer of the driver you plan to convert 202 203Clean up mmap forwarding 204------------------------ 205 206A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 207And also a lot of them forward dma-buf mmap to the gem mmap implementations. 208Would be great to refactor this all into a set of small common helpers. 209 210Contact: Daniel Vetter 211 212Put a reservation_object into drm_gem_object 213-------------------------------------------- 214 215This would remove the need for the ->gem_prime_res_obj callback. It would also 216allow us to implement generic helpers for waiting for a bo, allowing for quite a 217bit of refactoring in the various wait ioctl implementations. 218 219Contact: Daniel Vetter 220 221idr_init_base() 222--------------- 223 224DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 225userspace IDs to internal objects, and in most places ID=0 means NULL and hence 226is never used. Switching to idr_init_base() for these would make the idr more 227efficient. 228 229Contact: Daniel Vetter 230 231Defaults for .gem_prime_import and export 232----------------------------------------- 233 234Most drivers don't need to set drm_driver->gem_prime_import and 235->gem_prime_export now that drm_gem_prime_import() and drm_gem_prime_export() 236are the default. 237 238struct drm_gem_object_funcs 239--------------------------- 240 241GEM objects can now have a function table instead of having the callbacks on the 242DRM driver struct. This is now the preferred way and drivers can be moved over. 243 244Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 245--------------------------------------------------------- 246 247For cases where drivers are attempting to grab the modeset locks with a local 248acquire context. Replace the boilerplate code surrounding 249drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 250DRM_MODESET_LOCK_ALL_END() instead. 251 252This should also be done for all places where drm_modest_lock_all() is still 253used. 254 255As a reference, take a look at the conversions already completed in drm core. 256 257Contact: Sean Paul, respective driver maintainers 258 259Core refactorings 260================= 261 262Clean up the DRM header mess 263---------------------------- 264 265The DRM subsystem originally had only one huge global header, ``drmP.h``. This 266is now split up, but many source files still include it. The remaining part of 267the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the 268headers needed (and fixing up any missing pre-declarations in the headers). 269 270In the end no .c file should need to include ``drmP.h`` anymore. 271 272Contact: Daniel Vetter 273 274Add missing kerneldoc for exported functions 275-------------------------------------------- 276 277The DRM reference documentation is still lacking kerneldoc in a few areas. The 278task would be to clean up interfaces like moving functions around between 279files to better group them and improving the interfaces like dropping return 280values for functions that never fail. Then write kerneldoc for all exported 281functions and an overview section and integrate it all into the drm book. 282 283See https://dri.freedesktop.org/docs/drm/ for what's there already. 284 285Contact: Daniel Vetter 286 287Make panic handling work 288------------------------ 289 290This is a really varied tasks with lots of little bits and pieces: 291 292* The panic path can't be tested currently, leading to constant breaking. The 293 main issue here is that panics can be triggered from hardirq contexts and 294 hence all panic related callback can run in hardirq context. It would be 295 awesome if we could test at least the fbdev helper code and driver code by 296 e.g. trigger calls through drm debugfs files. hardirq context could be 297 achieved by using an IPI to the local processor. 298 299* There's a massive confusion of different panic handlers. DRM fbdev emulation 300 helpers have one, but on top of that the fbcon code itself also has one. We 301 need to make sure that they stop fighting over each another. 302 303* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 304 isn't a full solution for panic paths. We need to make sure that it only 305 returns true if there's a panic going on for real, and fix up all the 306 fallout. 307 308* The panic handler must never sleep, which also means it can't ever 309 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 310 even spinlocks (because NMI and hardirq can panic too). We need to either 311 make sure to not call such paths, or trylock everything. Really tricky. 312 313* For the above locking troubles reasons it's pretty much impossible to 314 attempt a synchronous modeset from panic handlers. The only thing we could 315 try to achive is an atomic ``set_base`` of the primary plane, and hope that 316 it shows up. Everything else probably needs to be delayed to some worker or 317 something else which happens later on. Otherwise it just kills the box 318 harder, prevent the panic from going out on e.g. netconsole. 319 320* There's also proposal for a simplied DRM console instead of the full-blown 321 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 322 obviously work for both console, in case we ever get kmslog merged. 323 324Contact: Daniel Vetter 325 326Clean up the debugfs support 327---------------------------- 328 329There's a bunch of issues with it: 330 331- The drm_info_list ->show() function doesn't even bother to cast to the drm 332 structure for you. This is lazy. 333 334- We probably want to have some support for debugfs files on crtc/connectors and 335 maybe other kms objects directly in core. There's even drm_print support in 336 the funcs for these objects to dump kms state, so it's all there. And then the 337 ->show() functions should obviously give you a pointer to the right object. 338 339- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 340 anything we want to print drm_device (or maybe drm_file) is the right thing. 341 342- The drm_driver->debugfs_init hooks we have is just an artifact of the old 343 midlayered load sequence. DRM debugfs should work more like sysfs, where you 344 can create properties/files for an object anytime you want, and the core 345 takes care of publishing/unpuplishing all the files at register/unregister 346 time. Drivers shouldn't need to worry about these technicalities, and fixing 347 this (together with the drm_minor->drm_device move) would allow us to remove 348 debugfs_init. 349 350Contact: Daniel Vetter 351 352KMS cleanups 353------------ 354 355Some of these date from the very introduction of KMS in 2008 ... 356 357- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should 358 be renamed to drm_mode_config.object_idr. 359 360- drm_display_mode doesn't need to be derived from drm_mode_object. That's 361 leftovers from older (never merged into upstream) KMS designs where modes 362 where set using their ID, including support to add/remove modes. 363 364- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 365 function tables in drivers, but before we can remove them we need to make sure 366 that all the users in helpers and drivers do correctly check for a NULL 367 vtable. 368 369- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 370 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 371 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 372 historical reasons) misnamed drm_primary_helper_destroy() function. 373 374Better Testing 375============== 376 377Enable trinity for DRM 378---------------------- 379 380And fix up the fallout. Should be really interesting ... 381 382Make KMS tests in i-g-t generic 383------------------------------- 384 385The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 386including tons of testcases for corner-cases in the modesetting API. It would 387be awesome if those tests (at least the ones not relying on Intel-specific GEM 388features) could be made to run on any KMS driver. 389 390Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 391converting things over. For modeset tests we also first need a bit of 392infrastructure to use dumb buffers for untiled buffers, to be able to run all 393the non-i915 specific modeset tests. 394 395Extend virtual test driver (VKMS) 396--------------------------------- 397 398See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 399internship task, since it only requires a virtual machine and can be sized to 400fit the available time. 401 402Contact: Daniel Vetter 403 404Driver Specific 405=============== 406 407tinydrm 408------- 409 410Tinydrm is the helper driver for really simple fb drivers. The goal is to make 411those drivers as simple as possible, so lots of room for refactoring: 412 413- backlight helpers, probably best to put them into a new drm_backlight.c. 414 This is because drivers/video is de-facto unmaintained. We could also 415 move drivers/video/backlight to drivers/gpu/backlight and take it all 416 over within drm-misc, but that's more work. Backlight helpers require a fair 417 bit of reworking and refactoring. A simple example is the enabling of a backlight. 418 Tinydrm has helpers for this. It would be good if other drivers can also use the 419 helper. However, there are various cases we need to consider i.e different 420 drivers seem to have different ways of enabling/disabling a backlight. 421 We also need to consider the backlight drivers (like gpio_backlight). The situation 422 is further complicated by the fact that the backlight is tied to fbdev 423 via fb_notifier_callback() which has complicated logic. For further details, refer 424 to the following discussion thread: 425 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 426 427- spi helpers, probably best put into spi core/helper code. Thierry said 428 the spi maintainer is fast&reactive, so shouldn't be a big issue. 429 430- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 431 least) into a separate helper, like we have for mipi-dsi already. Or follow 432 one of the ideas for having a shared dsi/dbi helper, abstracting away the 433 transport details more. 434 435- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma 436 helpers, as a _vmapped variant (since not every driver needs the vmap). 437 And tinydrm_gem_cma_free_object could the be merged into 438 drm_gem_cma_free_object(). 439 440- tinydrm_fb_create we could move into drm_simple_pipe, only need to add 441 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a 442 bunch of things (since it gives you a one-stop vfunc for simple drivers). 443 444- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 445 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 446 too :-) 447 448- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. 449 450Contact: Noralf Trønnes, Daniel Vetter 451 452AMD DC Display Driver 453--------------------- 454 455AMD DC is the display driver for AMD devices starting with Vega. There has been 456a bunch of progress cleaning it up but there's still plenty of work to be done. 457 458See drivers/gpu/drm/amd/display/TODO for tasks. 459 460Contact: Harry Wentland, Alex Deucher 461 462i915 463---- 464 465- Our early/late pm callbacks could be removed in favour of using 466 device_link_add to model the dependency between i915 and snd_had. See 467 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html 468 469Outside DRM 470=========== 471