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instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Convert existing KMS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 85Fallout from atomic KMS 86----------------------- 87 88``drm_atomic_helper.c`` provides a batch of functions which implement legacy 89IOCTLs on top of the new atomic driver interface. Which is really nice for 90gradual conversion of drivers, but unfortunately the semantic mismatches are 91a bit too severe. So there's some follow-up work to adjust the function 92interfaces to fix these issues: 93 94* atomic needs the lock acquire context. At the moment that's passed around 95 implicitly with some horrible hacks, and it's also allocate with 96 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 97 the acquire context explicitly on stack and then also pass it down into 98 drivers explicitly so that the legacy-on-atomic functions can use them. 99 100 Except for some driver code this is done. This task should be finished by 101 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 102 103* A bunch of the vtable hooks are now in the wrong place: DRM has a split 104 between core vfunc tables (named ``drm_foo_funcs``), which are used to 105 implement the userspace ABI. And then there's the optional hooks for the 106 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 107 internal use. Some of these hooks should be move from ``_funcs`` to 108 ``_helper_funcs`` since they are not part of the core ABI. There's a 109 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 110 111Contact: Daniel Vetter 112 113Get rid of dev->struct_mutex from GEM drivers 114--------------------------------------------- 115 116``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested 117everything. Nowadays in modern drivers the only bit where it's mandatory is 118serializing GEM buffer object destruction. Which unfortunately means drivers 119have to keep track of that lock and either call ``unreference`` or 120``unreference_locked`` depending upon context. 121 122Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, 123and there's a ``gem_free_object_unlocked`` callback for any drivers which are 124entirely ``struct_mutex`` free. 125 126For drivers that need ``struct_mutex`` it should be replaced with a driver- 127private lock. The tricky part is the BO free functions, since those can't 128reliably take that lock any more. Instead state needs to be protected with 129suitable subordinate locks or some cleanup work pushed to a worker thread. For 130performance-critical drivers it might also be better to go with a more 131fine-grained per-buffer object and per-context lockings scheme. Currently only the 132``msm`` driver still use ``struct_mutex``. 133 134Contact: Daniel Vetter, respective driver maintainers 135 136Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent 137---------------------------------------------------------------------------- 138 139For drivers which could have multiple instances, it is necessary to 140differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 141don't do this, drivers used dev_info/warn/err to make this differentiation. We 142now have DRM_DEV_* variants of the drm print macros, so we can start to convert 143those drivers back to using drm-formwatted specific log messages. 144 145Before you start this conversion please contact the relevant maintainers to make 146sure your work will be merged - not everyone agrees that the DRM dmesg macros 147are better. 148 149Contact: Sean Paul, Maintainer of the driver you plan to convert 150 151Convert drivers to use simple modeset suspend/resume 152---------------------------------------------------- 153 154Most drivers (except i915 and nouveau) that use 155drm_atomic_helper_suspend/resume() can probably be converted to use 156drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 157of the atomic suspend/resume code in older atomic modeset drivers. 158 159Contact: Maintainer of the driver you plan to convert 160 161Convert drivers to use drm_fb_helper_fbdev_setup/teardown() 162----------------------------------------------------------- 163 164Most drivers can use drm_fb_helper_fbdev_setup() except maybe: 165 166- amdgpu which has special logic to decide whether to call 167 drm_helper_disable_unused_functions() 168 169- armada which isn't atomic and doesn't call 170 drm_helper_disable_unused_functions() 171 172- i915 which calls drm_fb_helper_initial_config() in a worker 173 174Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can 175probably use drm_fb_helper_fbdev_teardown(). 176 177Contact: Maintainer of the driver you plan to convert 178 179Clean up mmap forwarding 180------------------------ 181 182A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 183And also a lot of them forward dma-buf mmap to the gem mmap implementations. 184Would be great to refactor this all into a set of small common helpers. 185 186Contact: Daniel Vetter 187 188Generic fbdev defio support 189--------------------------- 190 191The defio support code in the fbdev core has some very specific requirements, 192which means drivers need to have a special framebuffer for fbdev. Which prevents 193us from using the generic fbdev emulation code everywhere. The main issue is 194that it uses some fields in struct page itself, which breaks shmem gem objects 195(and other things). 196 197Possible solution would be to write our own defio mmap code in the drm fbdev 198emulation. It would need to fully wrap the existing mmap ops, forwarding 199everything after it has done the write-protect/mkwrite trickery: 200 201- In the drm_fbdev_fb_mmap helper, if we need defio, change the 202 default page prots to write-protected with something like this:: 203 204 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 205 206- Set the mkwrite and fsync callbacks with similar implementions to the core 207 fbdev defio stuff. These should all work on plain ptes, they don't actually 208 require a struct page. uff. These should all work on plain ptes, they don't 209 actually require a struct page. 210 211- Track the dirty pages in a separate structure (bitfield with one bit per page 212 should work) to avoid clobbering struct page. 213 214Might be good to also have some igt testcases for this. 215 216Contact: Daniel Vetter, Noralf Tronnes 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 250Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 251--------------------------------------------------------- 252 253For cases where drivers are attempting to grab the modeset locks with a local 254acquire context. Replace the boilerplate code surrounding 255drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 256DRM_MODESET_LOCK_ALL_END() instead. 257 258This should also be done for all places where drm_modest_lock_all() is still 259used. 260 261As a reference, take a look at the conversions already completed in drm core. 262 263Contact: Sean Paul, respective driver maintainers 264 265Core refactorings 266================= 267 268Clean up the DRM header mess 269---------------------------- 270 271The DRM subsystem originally had only one huge global header, ``drmP.h``. This 272is now split up, but many source files still include it. The remaining part of 273the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the 274headers needed (and fixing up any missing pre-declarations in the headers). 275 276In the end no .c file should need to include ``drmP.h`` anymore. 277 278Contact: Daniel Vetter 279 280Add missing kerneldoc for exported functions 281-------------------------------------------- 282 283The DRM reference documentation is still lacking kerneldoc in a few areas. The 284task would be to clean up interfaces like moving functions around between 285files to better group them and improving the interfaces like dropping return 286values for functions that never fail. Then write kerneldoc for all exported 287functions and an overview section and integrate it all into the drm book. 288 289See https://dri.freedesktop.org/docs/drm/ for what's there already. 290 291Contact: Daniel Vetter 292 293Make panic handling work 294------------------------ 295 296This is a really varied tasks with lots of little bits and pieces: 297 298* The panic path can't be tested currently, leading to constant breaking. The 299 main issue here is that panics can be triggered from hardirq contexts and 300 hence all panic related callback can run in hardirq context. It would be 301 awesome if we could test at least the fbdev helper code and driver code by 302 e.g. trigger calls through drm debugfs files. hardirq context could be 303 achieved by using an IPI to the local processor. 304 305* There's a massive confusion of different panic handlers. DRM fbdev emulation 306 helpers have one, but on top of that the fbcon code itself also has one. We 307 need to make sure that they stop fighting over each another. 308 309* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 310 isn't a full solution for panic paths. We need to make sure that it only 311 returns true if there's a panic going on for real, and fix up all the 312 fallout. 313 314* The panic handler must never sleep, which also means it can't ever 315 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 316 even spinlocks (because NMI and hardirq can panic too). We need to either 317 make sure to not call such paths, or trylock everything. Really tricky. 318 319* For the above locking troubles reasons it's pretty much impossible to 320 attempt a synchronous modeset from panic handlers. The only thing we could 321 try to achive is an atomic ``set_base`` of the primary plane, and hope that 322 it shows up. Everything else probably needs to be delayed to some worker or 323 something else which happens later on. Otherwise it just kills the box 324 harder, prevent the panic from going out on e.g. netconsole. 325 326* There's also proposal for a simplied DRM console instead of the full-blown 327 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 328 obviously work for both console, in case we ever get kmslog merged. 329 330Contact: Daniel Vetter 331 332Clean up the debugfs support 333---------------------------- 334 335There's a bunch of issues with it: 336 337- The drm_info_list ->show() function doesn't even bother to cast to the drm 338 structure for you. This is lazy. 339 340- We probably want to have some support for debugfs files on crtc/connectors and 341 maybe other kms objects directly in core. There's even drm_print support in 342 the funcs for these objects to dump kms state, so it's all there. And then the 343 ->show() functions should obviously give you a pointer to the right object. 344 345- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 346 anything we want to print drm_device (or maybe drm_file) is the right thing. 347 348- The drm_driver->debugfs_init hooks we have is just an artifact of the old 349 midlayered load sequence. DRM debugfs should work more like sysfs, where you 350 can create properties/files for an object anytime you want, and the core 351 takes care of publishing/unpuplishing all the files at register/unregister 352 time. Drivers shouldn't need to worry about these technicalities, and fixing 353 this (together with the drm_minor->drm_device move) would allow us to remove 354 debugfs_init. 355 356Contact: Daniel Vetter 357 358KMS cleanups 359------------ 360 361Some of these date from the very introduction of KMS in 2008 ... 362 363- drm_display_mode doesn't need to be derived from drm_mode_object. That's 364 leftovers from older (never merged into upstream) KMS designs where modes 365 where set using their ID, including support to add/remove modes. 366 367- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty 368 function tables in drivers, but before we can remove them we need to make sure 369 that all the users in helpers and drivers do correctly check for a NULL 370 vtable. 371 372- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the 373 drm_*_cleanup implementations and can be removed. Some tack a kfree() at the 374 end, for which we could add drm_*_cleanup_kfree(). And then there's the (for 375 historical reasons) misnamed drm_primary_helper_destroy() function. 376 377Better Testing 378============== 379 380Enable trinity for DRM 381---------------------- 382 383And fix up the fallout. Should be really interesting ... 384 385Make KMS tests in i-g-t generic 386------------------------------- 387 388The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 389including tons of testcases for corner-cases in the modesetting API. It would 390be awesome if those tests (at least the ones not relying on Intel-specific GEM 391features) could be made to run on any KMS driver. 392 393Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 394converting things over. For modeset tests we also first need a bit of 395infrastructure to use dumb buffers for untiled buffers, to be able to run all 396the non-i915 specific modeset tests. 397 398Extend virtual test driver (VKMS) 399--------------------------------- 400 401See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 402internship task, since it only requires a virtual machine and can be sized to 403fit the available time. 404 405Contact: Daniel Vetter 406 407Driver Specific 408=============== 409 410tinydrm 411------- 412 413Tinydrm is the helper driver for really simple fb drivers. The goal is to make 414those drivers as simple as possible, so lots of room for refactoring: 415 416- backlight helpers, probably best to put them into a new drm_backlight.c. 417 This is because drivers/video is de-facto unmaintained. We could also 418 move drivers/video/backlight to drivers/gpu/backlight and take it all 419 over within drm-misc, but that's more work. Backlight helpers require a fair 420 bit of reworking and refactoring. A simple example is the enabling of a backlight. 421 Tinydrm has helpers for this. It would be good if other drivers can also use the 422 helper. However, there are various cases we need to consider i.e different 423 drivers seem to have different ways of enabling/disabling a backlight. 424 We also need to consider the backlight drivers (like gpio_backlight). The situation 425 is further complicated by the fact that the backlight is tied to fbdev 426 via fb_notifier_callback() which has complicated logic. For further details, refer 427 to the following discussion thread: 428 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 429 430- spi helpers, probably best put into spi core/helper code. Thierry said 431 the spi maintainer is fast&reactive, so shouldn't be a big issue. 432 433- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 434 least) into a separate helper, like we have for mipi-dsi already. Or follow 435 one of the ideas for having a shared dsi/dbi helper, abstracting away the 436 transport details more. 437 438- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 439 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 440 too :-) 441 442Contact: Noralf Trønnes, Daniel Vetter 443 444AMD DC Display Driver 445--------------------- 446 447AMD DC is the display driver for AMD devices starting with Vega. There has been 448a bunch of progress cleaning it up but there's still plenty of work to be done. 449 450See drivers/gpu/drm/amd/display/TODO for tasks. 451 452Contact: Harry Wentland, Alex Deucher 453 454i915 455---- 456 457- Our early/late pm callbacks could be removed in favour of using 458 device_link_add to model the dependency between i915 and snd_had. See 459 https://dri.freedesktop.org/docs/drm/driver-api/device_link.html 460 461Outside DRM 462=========== 463