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. This task should be finished by 131 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 132 133* A bunch of the vtable hooks are now in the wrong place: DRM has a split 134 between core vfunc tables (named ``drm_foo_funcs``), which are used to 135 implement the userspace ABI. And then there's the optional hooks for the 136 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 137 internal use. Some of these hooks should be move from ``_funcs`` to 138 ``_helper_funcs`` since they are not part of the core ABI. There's a 139 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 140 141Contact: Daniel Vetter 142 143Get rid of dev->struct_mutex from GEM drivers 144--------------------------------------------- 145 146``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 147everything. Nowadays in modern drivers the only bit where it's mandatory is 148serializing GEM buffer object destruction. Which unfortunately means drivers 149have to keep track of that lock and either call ``unreference`` or 150``unreference_locked`` depending upon context. 151 152Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 153and there's a ``gem_free_object_unlocked`` callback for any drivers which are 154entirely ``struct_mutex`` free. 155 156For drivers that need ``struct_mutex`` it should be replaced with a driver- 157private lock. The tricky part is the BO free functions, since those can't 158reliably take that lock any more. Instead state needs to be protected with 159suitable subordinate locks or some cleanup work pushed to a worker thread. For 160performance-critical drivers it might also be better to go with a more 161fine-grained per-buffer object and per-context lockings scheme. Currently only the 162``msm`` driver still use ``struct_mutex``. 163 164Contact: Daniel Vetter, respective driver maintainers 165 166Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent 167---------------------------------------------------------------------------- 168 169For drivers which could have multiple instances, it is necessary to 170differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 171don't do this, drivers used dev_info/warn/err to make this differentiation. We 172now have DRM_DEV_* variants of the drm print macros, so we can start to convert 173those drivers back to using drm-formwatted specific log messages. 174 175Before you start this conversion please contact the relevant maintainers to make 176sure your work will be merged - not everyone agrees that the DRM dmesg macros 177are better. 178 179Contact: Sean Paul, Maintainer of the driver you plan to convert 180 181Convert drivers to use simple modeset suspend/resume 182---------------------------------------------------- 183 184Most drivers (except i915 and nouveau) that use 185drm_atomic_helper_suspend/resume() can probably be converted to use 186drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 187of the atomic suspend/resume code in older atomic modeset drivers. 188 189Contact: Maintainer of the driver you plan to convert 190 191Convert drivers to use drm_fb_helper_fbdev_setup/teardown() 192----------------------------------------------------------- 193 194Most drivers can use drm_fb_helper_fbdev_setup() except maybe: 195 196- amdgpu which has special logic to decide whether to call 197 drm_helper_disable_unused_functions() 198 199- armada which isn't atomic and doesn't call 200 drm_helper_disable_unused_functions() 201 202- i915 which calls drm_fb_helper_initial_config() in a worker 203 204Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can 205probably use drm_fb_helper_fbdev_teardown(). 206 207Contact: Maintainer of the driver you plan to convert 208 209Clean up mmap forwarding 210------------------------ 211 212A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 213And also a lot of them forward dma-buf mmap to the gem mmap implementations. 214Would be great to refactor this all into a set of small common helpers. 215 216Contact: Daniel Vetter 217 218Put a reservation_object into drm_gem_object 219-------------------------------------------- 220 221This would remove the need for the ->gem_prime_res_obj callback. It would also 222allow us to implement generic helpers for waiting for a bo, allowing for quite a 223bit of refactoring in the various wait ioctl implementations. 224 225Contact: Daniel Vetter 226 227idr_init_base() 228--------------- 229 230DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 231userspace IDs to internal objects, and in most places ID=0 means NULL and hence 232is never used. Switching to idr_init_base() for these would make the idr more 233efficient. 234 235Contact: Daniel Vetter 236 237Defaults for .gem_prime_import and export 238----------------------------------------- 239 240Most drivers don't need to set drm_driver->gem_prime_import and 241->gem_prime_export now that drm_gem_prime_import() and drm_gem_prime_export() 242are the default. 243 244struct drm_gem_object_funcs 245--------------------------- 246 247GEM objects can now have a function table instead of having the callbacks on the 248DRM driver struct. This is now the preferred way and drivers can be moved over. 249 250Core refactorings 251================= 252 253Clean up the DRM header mess 254---------------------------- 255 256The DRM subsystem originally had only one huge global header, ``drmP.h``. This 257is now split up, but many source files still include it. The remaining part of 258the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the 259headers needed (and fixing up any missing pre-declarations in the headers). 260 261In the end no .c file should need to include ``drmP.h`` anymore. 262 263Contact: Daniel Vetter 264 265Add missing kerneldoc for exported functions 266-------------------------------------------- 267 268The DRM reference documentation is still lacking kerneldoc in a few areas. The 269task would be to clean up interfaces like moving functions around between 270files to better group them and improving the interfaces like dropping return 271values for functions that never fail. Then write kerneldoc for all exported 272functions and an overview section and integrate it all into the drm book. 273 274See https://dri.freedesktop.org/docs/drm/ for what's there already. 275 276Contact: Daniel Vetter 277 278Make panic handling work 279------------------------ 280 281This is a really varied tasks with lots of little bits and pieces: 282 283* The panic path can't be tested currently, leading to constant breaking. The 284 main issue here is that panics can be triggered from hardirq contexts and 285 hence all panic related callback can run in hardirq context. It would be 286 awesome if we could test at least the fbdev helper code and driver code by 287 e.g. trigger calls through drm debugfs files. hardirq context could be 288 achieved by using an IPI to the local processor. 289 290* There's a massive confusion of different panic handlers. DRM fbdev emulation 291 helpers have one, but on top of that the fbcon code itself also has one. We 292 need to make sure that they stop fighting over each another. 293 294* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 295 isn't a full solution for panic paths. We need to make sure that it only 296 returns true if there's a panic going on for real, and fix up all the 297 fallout. 298 299* The panic handler must never sleep, which also means it can't ever 300 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 301 even spinlocks (because NMI and hardirq can panic too). We need to either 302 make sure to not call such paths, or trylock everything. Really tricky. 303 304* For the above locking troubles reasons it's pretty much impossible to 305 attempt a synchronous modeset from panic handlers. The only thing we could 306 try to achive is an atomic ``set_base`` of the primary plane, and hope that 307 it shows up. Everything else probably needs to be delayed to some worker or 308 something else which happens later on. Otherwise it just kills the box 309 harder, prevent the panic from going out on e.g. netconsole. 310 311* There's also proposal for a simplied DRM console instead of the full-blown 312 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 313 obviously work for both console, in case we ever get kmslog merged. 314 315Contact: Daniel Vetter 316 317Clean up the debugfs support 318---------------------------- 319 320There's a bunch of issues with it: 321 322- The drm_info_list ->show() function doesn't even bother to cast to the drm 323 structure for you. This is lazy. 324 325- We probably want to have some support for debugfs files on crtc/connectors and 326 maybe other kms objects directly in core. There's even drm_print support in 327 the funcs for these objects to dump kms state, so it's all there. And then the 328 ->show() functions should obviously give you a pointer to the right object. 329 330- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 331 anything we want to print drm_device (or maybe drm_file) is the right thing. 332 333- The drm_driver->debugfs_init hooks we have is just an artifact of the old 334 midlayered load sequence. DRM debugfs should work more like sysfs, where you 335 can create properties/files for an object anytime you want, and the core 336 takes care of publishing/unpuplishing all the files at register/unregister 337 time. Drivers shouldn't need to worry about these technicalities, and fixing 338 this (together with the drm_minor->drm_device move) would allow us to remove 339 debugfs_init. 340 341Contact: Daniel Vetter 342 343KMS cleanups 344------------ 345 346Some of these date from the very introduction of KMS in 2008 ... 347 348- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should 349 be renamed to drm_mode_config.object_idr. 350 351- drm_display_mode doesn't need to be derived from drm_mode_object. That's 352 leftovers from older (never merged into upstream) KMS designs where modes 353 where set using their ID, including support to add/remove modes. 354 355- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 356 function tables in drivers, but before we can remove them we need to make sure 357 that all the users in helpers and drivers do correctly check for a NULL 358 vtable. 359 360- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 361 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 362 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 363 historical reasons) misnamed drm_primary_helper_destroy() function. 364 365Better Testing 366============== 367 368Enable trinity for DRM 369---------------------- 370 371And fix up the fallout. Should be really interesting ... 372 373Make KMS tests in i-g-t generic 374------------------------------- 375 376The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 377including tons of testcases for corner-cases in the modesetting API. It would 378be awesome if those tests (at least the ones not relying on Intel-specific GEM 379features) could be made to run on any KMS driver. 380 381Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 382converting things over. For modeset tests we also first need a bit of 383infrastructure to use dumb buffers for untiled buffers, to be able to run all 384the non-i915 specific modeset tests. 385 386Extend virtual test driver (VKMS) 387--------------------------------- 388 389See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 390internship task, since it only requires a virtual machine and can be sized to 391fit the available time. 392 393Contact: Daniel Vetter 394 395Driver Specific 396=============== 397 398tinydrm 399------- 400 401Tinydrm is the helper driver for really simple fb drivers. The goal is to make 402those drivers as simple as possible, so lots of room for refactoring: 403 404- backlight helpers, probably best to put them into a new drm_backlight.c. 405 This is because drivers/video is de-facto unmaintained. We could also 406 move drivers/video/backlight to drivers/gpu/backlight and take it all 407 over within drm-misc, but that's more work. Backlight helpers require a fair 408 bit of reworking and refactoring. A simple example is the enabling of a backlight. 409 Tinydrm has helpers for this. It would be good if other drivers can also use the 410 helper. However, there are various cases we need to consider i.e different 411 drivers seem to have different ways of enabling/disabling a backlight. 412 We also need to consider the backlight drivers (like gpio_backlight). The situation 413 is further complicated by the fact that the backlight is tied to fbdev 414 via fb_notifier_callback() which has complicated logic. For further details, refer 415 to the following discussion thread: 416 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 417 418- spi helpers, probably best put into spi core/helper code. Thierry said 419 the spi maintainer is fast&reactive, so shouldn't be a big issue. 420 421- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 422 least) into a separate helper, like we have for mipi-dsi already. Or follow 423 one of the ideas for having a shared dsi/dbi helper, abstracting away the 424 transport details more. 425 426- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma 427 helpers, as a _vmapped variant (since not every driver needs the vmap). 428 And tinydrm_gem_cma_free_object could the be merged into 429 drm_gem_cma_free_object(). 430 431- tinydrm_fb_create we could move into drm_simple_pipe, only need to add 432 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a 433 bunch of things (since it gives you a one-stop vfunc for simple drivers). 434 435- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 436 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 437 too :-) 438 439- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. 440 441Contact: Noralf Trønnes, Daniel Vetter 442 443AMD DC Display Driver 444--------------------- 445 446AMD DC is the display driver for AMD devices starting with Vega. There has been 447a bunch of progress cleaning it up but there's still plenty of work to be done. 448 449See drivers/gpu/drm/amd/display/TODO for tasks. 450 451Contact: Harry Wentland, Alex Deucher 452 453i915 454---- 455 456- Our early/late pm callbacks could be removed in favour of using 457 device_link_add to model the dependency between i915 and snd_had. See 458 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html 459 460Outside DRM 461=========== 462