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 237Core refactorings 238================= 239 240Clean up the DRM header mess 241---------------------------- 242 243The DRM subsystem originally had only one huge global header, ``drmP.h``. This 244is now split up, but many source files still include it. The remaining part of 245the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the 246headers needed (and fixing up any missing pre-declarations in the headers). 247 248In the end no .c file should need to include ``drmP.h`` anymore. 249 250Contact: Daniel Vetter 251 252Add missing kerneldoc for exported functions 253-------------------------------------------- 254 255The DRM reference documentation is still lacking kerneldoc in a few areas. The 256task would be to clean up interfaces like moving functions around between 257files to better group them and improving the interfaces like dropping return 258values for functions that never fail. Then write kerneldoc for all exported 259functions and an overview section and integrate it all into the drm book. 260 261See https://dri.freedesktop.org/docs/drm/ for what's there already. 262 263Contact: Daniel Vetter 264 265Make panic handling work 266------------------------ 267 268This is a really varied tasks with lots of little bits and pieces: 269 270* The panic path can't be tested currently, leading to constant breaking. The 271 main issue here is that panics can be triggered from hardirq contexts and 272 hence all panic related callback can run in hardirq context. It would be 273 awesome if we could test at least the fbdev helper code and driver code by 274 e.g. trigger calls through drm debugfs files. hardirq context could be 275 achieved by using an IPI to the local processor. 276 277* There's a massive confusion of different panic handlers. DRM fbdev emulation 278 helpers have one, but on top of that the fbcon code itself also has one. We 279 need to make sure that they stop fighting over each another. 280 281* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 282 isn't a full solution for panic paths. We need to make sure that it only 283 returns true if there's a panic going on for real, and fix up all the 284 fallout. 285 286* The panic handler must never sleep, which also means it can't ever 287 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 288 even spinlocks (because NMI and hardirq can panic too). We need to either 289 make sure to not call such paths, or trylock everything. Really tricky. 290 291* For the above locking troubles reasons it's pretty much impossible to 292 attempt a synchronous modeset from panic handlers. The only thing we could 293 try to achive is an atomic ``set_base`` of the primary plane, and hope that 294 it shows up. Everything else probably needs to be delayed to some worker or 295 something else which happens later on. Otherwise it just kills the box 296 harder, prevent the panic from going out on e.g. netconsole. 297 298* There's also proposal for a simplied DRM console instead of the full-blown 299 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 300 obviously work for both console, in case we ever get kmslog merged. 301 302Contact: Daniel Vetter 303 304Clean up the debugfs support 305---------------------------- 306 307There's a bunch of issues with it: 308 309- The drm_info_list ->show() function doesn't even bother to cast to the drm 310 structure for you. This is lazy. 311 312- We probably want to have some support for debugfs files on crtc/connectors and 313 maybe other kms objects directly in core. There's even drm_print support in 314 the funcs for these objects to dump kms state, so it's all there. And then the 315 ->show() functions should obviously give you a pointer to the right object. 316 317- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 318 anything we want to print drm_device (or maybe drm_file) is the right thing. 319 320- The drm_driver->debugfs_init hooks we have is just an artifact of the old 321 midlayered load sequence. DRM debugfs should work more like sysfs, where you 322 can create properties/files for an object anytime you want, and the core 323 takes care of publishing/unpuplishing all the files at register/unregister 324 time. Drivers shouldn't need to worry about these technicalities, and fixing 325 this (together with the drm_minor->drm_device move) would allow us to remove 326 debugfs_init. 327 328Contact: Daniel Vetter 329 330KMS cleanups 331------------ 332 333Some of these date from the very introduction of KMS in 2008 ... 334 335- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should 336 be renamed to drm_mode_config.object_idr. 337 338- drm_display_mode doesn't need to be derived from drm_mode_object. That's 339 leftovers from older (never merged into upstream) KMS designs where modes 340 where set using their ID, including support to add/remove modes. 341 342Better Testing 343============== 344 345Enable trinity for DRM 346---------------------- 347 348And fix up the fallout. Should be really interesting ... 349 350Make KMS tests in i-g-t generic 351------------------------------- 352 353The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 354including tons of testcases for corner-cases in the modesetting API. It would 355be awesome if those tests (at least the ones not relying on Intel-specific GEM 356features) could be made to run on any KMS driver. 357 358Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 359converting things over. For modeset tests we also first need a bit of 360infrastructure to use dumb buffers for untiled buffers, to be able to run all 361the non-i915 specific modeset tests. 362 363Extend virtual test driver (VKMS) 364--------------------------------- 365 366See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 367internship task, since it only requires a virtual machine and can be sized to 368fit the available time. 369 370Contact: Daniel Vetter 371 372Driver Specific 373=============== 374 375tinydrm 376------- 377 378Tinydrm is the helper driver for really simple fb drivers. The goal is to make 379those drivers as simple as possible, so lots of room for refactoring: 380 381- backlight helpers, probably best to put them into a new drm_backlight.c. 382 This is because drivers/video is de-facto unmaintained. We could also 383 move drivers/video/backlight to drivers/gpu/backlight and take it all 384 over within drm-misc, but that's more work. Backlight helpers require a fair 385 bit of reworking and refactoring. A simple example is the enabling of a backlight. 386 Tinydrm has helpers for this. It would be good if other drivers can also use the 387 helper. However, there are various cases we need to consider i.e different 388 drivers seem to have different ways of enabling/disabling a backlight. 389 We also need to consider the backlight drivers (like gpio_backlight). The situation 390 is further complicated by the fact that the backlight is tied to fbdev 391 via fb_notifier_callback() which has complicated logic. For further details, refer 392 to the following discussion thread: 393 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 394 395- spi helpers, probably best put into spi core/helper code. Thierry said 396 the spi maintainer is fast&reactive, so shouldn't be a big issue. 397 398- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 399 least) into a separate helper, like we have for mipi-dsi already. Or follow 400 one of the ideas for having a shared dsi/dbi helper, abstracting away the 401 transport details more. 402 403- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma 404 helpers, as a _vmapped variant (since not every driver needs the vmap). 405 And tinydrm_gem_cma_free_object could the be merged into 406 drm_gem_cma_free_object(). 407 408- tinydrm_fb_create we could move into drm_simple_pipe, only need to add 409 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a 410 bunch of things (since it gives you a one-stop vfunc for simple drivers). 411 412- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 413 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 414 too :-) 415 416- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. 417 418Contact: Noralf Trønnes, Daniel Vetter 419 420AMD DC Display Driver 421--------------------- 422 423AMD DC is the display driver for AMD devices starting with Vega. There has been 424a bunch of progress cleaning it up but there's still plenty of work to be done. 425 426See drivers/gpu/drm/amd/display/TODO for tasks. 427 428Contact: Harry Wentland, Alex Deucher 429 430i915 431---- 432 433- Our early/late pm callbacks could be removed in favour of using 434 device_link_add to model the dependency between i915 and snd_had. See 435 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html 436 437Outside DRM 438=========== 439