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 31Switch from reference/unreference to get/put 32-------------------------------------------- 33 34For some reason DRM core uses ``reference``/``unreference`` suffixes for 35refcounting functions, but kernel uses ``get``/``put`` (e.g. 36``kref_get``/``put()``). It would be good to switch over for consistency, and 37it's shorter. Needs to be done in 3 steps for each pair of functions: 38 39* Create new ``get``/``put`` functions, define the old names as compatibility 40 wrappers 41* Switch over each file/driver using a cocci-generated spatch. 42* Once all users of the old names are gone, remove them. 43 44This way drivers/patches in the progress of getting merged won't break. 45 46Contact: Daniel Vetter 47 48Convert existing KMS drivers to atomic modesetting 49-------------------------------------------------- 50 513.19 has the atomic modeset interfaces and helpers, so drivers can now be 52converted over. Modern compositors like Wayland or Surfaceflinger on Android 53really want an atomic modeset interface, so this is all about the bright 54future. 55 56There is a conversion guide for atomic and all you need is a GPU for a 57non-converted driver (again virtual HW drivers for KVM are still all 58suitable). 59 60As part of this drivers also need to convert to universal plane (which means 61exposing primary & cursor as proper plane objects). But that's much easier to 62do by directly using the new atomic helper driver callbacks. 63 64Contact: Daniel Vetter, respective driver maintainers 65 66Clean up the clipped coordination confusion around planes 67--------------------------------------------------------- 68 69We have a helper to get this right with drm_plane_helper_check_update(), but 70it's not consistently used. This should be fixed, preferrably in the atomic 71helpers (and drivers then moved over to clipped coordinates). Probably the 72helper should also be moved from drm_plane_helper.c to the atomic helpers, to 73avoid confusion - the other helpers in that file are all deprecated legacy 74helpers. 75 76Contact: Ville Syrjälä, Daniel Vetter, driver maintainers 77 78Convert early atomic drivers to async commit helpers 79---------------------------------------------------- 80 81For the first year the atomic modeset helpers didn't support asynchronous / 82nonblocking commits, and every driver had to hand-roll them. This is fixed 83now, but there's still a pile of existing drivers that easily could be 84converted over to the new infrastructure. 85 86One issue with the helpers is that they require that drivers handle completion 87events for atomic commits correctly. But fixing these bugs is good anyway. 88 89Contact: Daniel Vetter, respective driver maintainers 90 91Better manual-upload support for atomic 92--------------------------------------- 93 94This would be especially useful for tinydrm: 95 96- Add a struct drm_rect dirty_clip to drm_crtc_state. When duplicating the 97 crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in 98 __drm_atomic_helper_crtc_duplicate_state(). 99 100- Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_ 101 prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this 102 is a function useful to implement the fb->dirty function. 103 104- Create a new drm_fb_dirty function which does essentially what e.g. 105 mipi_dbi_fb_dirty does. You can use e.g. drm_atomic_helper_update_plane as the 106 template. But instead of doing a simple full-screen plane update, this new 107 helper also sets crtc_state->dirty_clip to the right coordinates. And of 108 course it needs to check whether the fb is actually active (and maybe where), 109 so there's some book-keeping involved. There's also some good fun involved in 110 scaling things appropriately. For that case we might simply give up and 111 declare the entire area covered by the plane as dirty. 112 113Contact: Noralf Trønnes, Daniel Vetter 114 115Fallout from atomic KMS 116----------------------- 117 118``drm_atomic_helper.c`` provides a batch of functions which implement legacy 119IOCTLs on top of the new atomic driver interface. Which is really nice for 120gradual conversion of drivers, but unfortunately the semantic mismatches are 121a bit too severe. So there's some follow-up work to adjust the function 122interfaces to fix these issues: 123 124* atomic needs the lock acquire context. At the moment that's passed around 125 implicitly with some horrible hacks, and it's also allocate with 126 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 127 the acquire context explicitly on stack and then also pass it down into 128 drivers explicitly so that the legacy-on-atomic functions can use them. 129 130 Except for some driver code this is done. 131 132* A bunch of the vtable hooks are now in the wrong place: DRM has a split 133 between core vfunc tables (named ``drm_foo_funcs``), which are used to 134 implement the userspace ABI. And then there's the optional hooks for the 135 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 136 internal use. Some of these hooks should be move from ``_funcs`` to 137 ``_helper_funcs`` since they are not part of the core ABI. There's a 138 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 139 140* There's a new helper ``drm_atomic_helper_best_encoder()`` which could be 141 used by all atomic drivers which don't select the encoder for a given 142 connector at runtime. That's almost all of them, and would allow us to get 143 rid of a lot of ``best_encoder`` boilerplate in drivers. 144 145 This was almost done, but new drivers added a few more cases again. 146 147Contact: Daniel Vetter 148 149Get rid of dev->struct_mutex from GEM drivers 150--------------------------------------------- 151 152``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 153everything. Nowadays in modern drivers the only bit where it's mandatory is 154serializing GEM buffer object destruction. Which unfortunately means drivers 155have to keep track of that lock and either call ``unreference`` or 156``unreference_locked`` depending upon context. 157 158Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 159and there's a ``gem_free_object_unlocked`` callback for any drivers which are 160entirely ``struct_mutex`` free. 161 162For drivers that need ``struct_mutex`` it should be replaced with a driver- 163private lock. The tricky part is the BO free functions, since those can't 164reliably take that lock any more. Instead state needs to be protected with 165suitable subordinate locks or some cleanup work pushed to a worker thread. For 166performance-critical drivers it might also be better to go with a more 167fine-grained per-buffer object and per-context lockings scheme. Currently the 168following drivers still use ``struct_mutex``: ``msm``, ``omapdrm`` and 169``udl``. 170 171Contact: Daniel Vetter, respective driver maintainers 172 173Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent 174---------------------------------------------------------------------------- 175 176For drivers which could have multiple instances, it is necessary to 177differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 178don't do this, drivers used dev_info/warn/err to make this differentiation. We 179now have DRM_DEV_* variants of the drm print macros, so we can start to convert 180those drivers back to using drm-formwatted specific log messages. 181 182Before you start this conversion please contact the relevant maintainers to make 183sure your work will be merged - not everyone agrees that the DRM dmesg macros 184are better. 185 186Contact: Sean Paul, Maintainer of the driver you plan to convert 187 188Convert drivers to use simple modeset suspend/resume 189---------------------------------------------------- 190 191Most drivers (except i915 and nouveau) that use 192drm_atomic_helper_suspend/resume() can probably be converted to use 193drm_mode_config_helper_suspend/resume(). 194 195Contact: Maintainer of the driver you plan to convert 196 197Convert drivers to use drm_fb_helper_fbdev_setup/teardown() 198----------------------------------------------------------- 199 200Most drivers can use drm_fb_helper_fbdev_setup() except maybe: 201 202- amdgpu which has special logic to decide whether to call 203 drm_helper_disable_unused_functions() 204 205- armada which isn't atomic and doesn't call 206 drm_helper_disable_unused_functions() 207 208- i915 which calls drm_fb_helper_initial_config() in a worker 209 210Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can 211probably use drm_fb_helper_fbdev_teardown(). 212 213Contact: Maintainer of the driver you plan to convert 214 215Clean up mmap forwarding 216------------------------ 217 218A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 219And also a lot of them forward dma-buf mmap to the gem mmap implementations. 220Would be great to refactor this all into a set of small common helpers. 221 222Contact: Daniel Vetter 223 224Put a reservation_object into drm_gem_object 225-------------------------------------------- 226 227This would remove the need for the ->gem_prime_res_obj callback. It would also 228allow us to implement generic helpers for waiting for a bo, allowing for quite a 229bit of refactoring in the various wait ioctl implementations. 230 231Contact: Daniel Vetter 232 233idr_init_base() 234--------------- 235 236DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 237userspace IDs to internal objects, and in most places ID=0 means NULL and hence 238is never used. Switching to idr_init_base() for these would make the idr more 239efficient. 240 241Contact: Daniel Vetter 242 243Core refactorings 244================= 245 246Clean up the DRM header mess 247---------------------------- 248 249Currently the DRM subsystem has only one global header, ``drmP.h``. This is 250used both for functions exported to helper libraries and drivers and functions 251only used internally in the ``drm.ko`` module. The goal would be to move all 252header declarations not needed outside of ``drm.ko`` into 253``drivers/gpu/drm/drm_*_internal.h`` header files. ``EXPORT_SYMBOL`` also 254needs to be dropped for these functions. 255 256This would nicely tie in with the below task to create kerneldoc after the API 257is cleaned up. Or with the "hide legacy cruft better" task. 258 259Note that this is well in progress, but ``drmP.h`` is still huge. The updated 260plan is to switch to per-file driver API headers, which will also structure 261the kerneldoc better. This should also allow more fine-grained ``#include`` 262directives. 263 264In the end no .c file should need to include ``drmP.h`` anymore. 265 266Contact: Daniel Vetter 267 268Add missing kerneldoc for exported functions 269-------------------------------------------- 270 271The DRM reference documentation is still lacking kerneldoc in a few areas. The 272task would be to clean up interfaces like moving functions around between 273files to better group them and improving the interfaces like dropping return 274values for functions that never fail. Then write kerneldoc for all exported 275functions and an overview section and integrate it all into the drm book. 276 277See https://dri.freedesktop.org/docs/drm/ for what's there already. 278 279Contact: Daniel Vetter 280 281Hide legacy cruft better 282------------------------ 283 284Way back DRM supported only drivers which shadow-attached to PCI devices with 285userspace or fbdev drivers setting up outputs. Modern DRM drivers take charge 286of the entire device, you can spot them with the DRIVER_MODESET flag. 287 288Unfortunately there's still large piles of legacy code around which needs to 289be hidden so that driver writers don't accidentally end up using it. And to 290prevent security issues in those legacy IOCTLs from being exploited on modern 291drivers. This has multiple possible subtasks: 292 293* Extract support code for legacy features into a ``drm-legacy.ko`` kernel 294 module and compile it only when one of the legacy drivers is enabled. 295 296This is mostly done, the only thing left is to split up ``drm_irq.c`` into 297legacy cruft and the parts needed by modern KMS drivers. 298 299Contact: Daniel Vetter 300 301Make panic handling work 302------------------------ 303 304This is a really varied tasks with lots of little bits and pieces: 305 306* The panic path can't be tested currently, leading to constant breaking. The 307 main issue here is that panics can be triggered from hardirq contexts and 308 hence all panic related callback can run in hardirq context. It would be 309 awesome if we could test at least the fbdev helper code and driver code by 310 e.g. trigger calls through drm debugfs files. hardirq context could be 311 achieved by using an IPI to the local processor. 312 313* There's a massive confusion of different panic handlers. DRM fbdev emulation 314 helpers have one, but on top of that the fbcon code itself also has one. We 315 need to make sure that they stop fighting over each another. 316 317* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 318 isn't a full solution for panic paths. We need to make sure that it only 319 returns true if there's a panic going on for real, and fix up all the 320 fallout. 321 322* The panic handler must never sleep, which also means it can't ever 323 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 324 even spinlocks (because NMI and hardirq can panic too). We need to either 325 make sure to not call such paths, or trylock everything. Really tricky. 326 327* For the above locking troubles reasons it's pretty much impossible to 328 attempt a synchronous modeset from panic handlers. The only thing we could 329 try to achive is an atomic ``set_base`` of the primary plane, and hope that 330 it shows up. Everything else probably needs to be delayed to some worker or 331 something else which happens later on. Otherwise it just kills the box 332 harder, prevent the panic from going out on e.g. netconsole. 333 334* There's also proposal for a simplied DRM console instead of the full-blown 335 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 336 obviously work for both console, in case we ever get kmslog merged. 337 338Contact: Daniel Vetter 339 340Clean up the debugfs support 341---------------------------- 342 343There's a bunch of issues with it: 344 345- The drm_info_list ->show() function doesn't even bother to cast to the drm 346 structure for you. This is lazy. 347 348- We probably want to have some support for debugfs files on crtc/connectors and 349 maybe other kms objects directly in core. There's even drm_print support in 350 the funcs for these objects to dump kms state, so it's all there. And then the 351 ->show() functions should obviously give you a pointer to the right object. 352 353- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 354 anything we want to print drm_device (or maybe drm_file) is the right thing. 355 356- The drm_driver->debugfs_init hooks we have is just an artifact of the old 357 midlayered load sequence. DRM debugfs should work more like sysfs, where you 358 can create properties/files for an object anytime you want, and the core 359 takes care of publishing/unpuplishing all the files at register/unregister 360 time. Drivers shouldn't need to worry about these technicalities, and fixing 361 this (together with the drm_minor->drm_device move) would allow us to remove 362 debugfs_init. 363 364Contact: Daniel Vetter 365 366KMS cleanups 367------------ 368 369Some of these date from the very introduction of KMS in 2008 ... 370 371- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should 372 be renamed to drm_mode_config.object_idr. 373 374- drm_display_mode doesn't need to be derived from drm_mode_object. That's 375 leftovers from older (never merged into upstream) KMS designs where modes 376 where set using their ID, including support to add/remove modes. 377 378Better Testing 379============== 380 381Enable trinity for DRM 382---------------------- 383 384And fix up the fallout. Should be really interesting ... 385 386Make KMS tests in i-g-t generic 387------------------------------- 388 389The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 390including tons of testcases for corner-cases in the modesetting API. It would 391be awesome if those tests (at least the ones not relying on Intel-specific GEM 392features) could be made to run on any KMS driver. 393 394Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 395converting things over. For modeset tests we also first need a bit of 396infrastructure to use dumb buffers for untiled buffers, to be able to run all 397the non-i915 specific modeset tests. 398 399Contact: Daniel Vetter 400 401Create a virtual KMS driver for testing (vkms) 402---------------------------------------------- 403 404With all the latest helpers it should be fairly simple to create a virtual KMS 405driver useful for testing, or for running X or similar on headless machines 406(to be able to still use the GPU). This would be similar to vgem, but aimed at 407the modeset side. 408 409Once the basics are there there's tons of possibilities to extend it. 410 411Contact: Daniel Vetter 412 413Driver Specific 414=============== 415 416tinydrm 417------- 418 419Tinydrm is the helper driver for really simple fb drivers. The goal is to make 420those drivers as simple as possible, so lots of room for refactoring: 421 422- backlight helpers, probably best to put them into a new drm_backlight.c. 423 This is because drivers/video is de-facto unmaintained. We could also 424 move drivers/video/backlight to drivers/gpu/backlight and take it all 425 over within drm-misc, but that's more work. Backlight helpers require a fair 426 bit of reworking and refactoring. A simple example is the enabling of a backlight. 427 Tinydrm has helpers for this. It would be good if other drivers can also use the 428 helper. However, there are various cases we need to consider i.e different 429 drivers seem to have different ways of enabling/disabling a backlight. 430 We also need to consider the backlight drivers (like gpio_backlight). The situation 431 is further complicated by the fact that the backlight is tied to fbdev 432 via fb_notifier_callback() which has complicated logic. For further details, refer 433 to the following discussion thread: 434 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 435 436- spi helpers, probably best put into spi core/helper code. Thierry said 437 the spi maintainer is fast&reactive, so shouldn't be a big issue. 438 439- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 440 least) into a separate helper, like we have for mipi-dsi already. Or follow 441 one of the ideas for having a shared dsi/dbi helper, abstracting away the 442 transport details more. 443 444- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma 445 helpers, as a _vmapped variant (since not every driver needs the vmap). 446 And tinydrm_gem_cma_free_object could the be merged into 447 drm_gem_cma_free_object(). 448 449- tinydrm_fb_create we could move into drm_simple_pipe, only need to add 450 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a 451 bunch of things (since it gives you a one-stop vfunc for simple drivers). 452 453- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 454 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 455 too :-) 456 457- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. 458 459Contact: Noralf Trønnes, Daniel Vetter 460 461AMD DC Display Driver 462--------------------- 463 464AMD DC is the display driver for AMD devices starting with Vega. There has been 465a bunch of progress cleaning it up but there's still plenty of work to be done. 466 467See drivers/gpu/drm/amd/display/TODO for tasks. 468 469Contact: Harry Wentland, Alex Deucher 470 471i915 472---- 473 474- Our early/late pm callbacks could be removed in favour of using 475 device_link_add to model the dependency between i915 and snd_had. See 476 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html 477 478Outside DRM 479=========== 480