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 182Contact: Sean Paul, Maintainer of the driver you plan to convert 183 184Core refactorings 185================= 186 187Clean up the DRM header mess 188---------------------------- 189 190Currently the DRM subsystem has only one global header, ``drmP.h``. This is 191used both for functions exported to helper libraries and drivers and functions 192only used internally in the ``drm.ko`` module. The goal would be to move all 193header declarations not needed outside of ``drm.ko`` into 194``drivers/gpu/drm/drm_*_internal.h`` header files. ``EXPORT_SYMBOL`` also 195needs to be dropped for these functions. 196 197This would nicely tie in with the below task to create kerneldoc after the API 198is cleaned up. Or with the "hide legacy cruft better" task. 199 200Note that this is well in progress, but ``drmP.h`` is still huge. The updated 201plan is to switch to per-file driver API headers, which will also structure 202the kerneldoc better. This should also allow more fine-grained ``#include`` 203directives. 204 205In the end no .c file should need to include ``drmP.h`` anymore. 206 207Contact: Daniel Vetter 208 209Add missing kerneldoc for exported functions 210-------------------------------------------- 211 212The DRM reference documentation is still lacking kerneldoc in a few areas. The 213task would be to clean up interfaces like moving functions around between 214files to better group them and improving the interfaces like dropping return 215values for functions that never fail. Then write kerneldoc for all exported 216functions and an overview section and integrate it all into the drm book. 217 218See https://dri.freedesktop.org/docs/drm/ for what's there already. 219 220Contact: Daniel Vetter 221 222Hide legacy cruft better 223------------------------ 224 225Way back DRM supported only drivers which shadow-attached to PCI devices with 226userspace or fbdev drivers setting up outputs. Modern DRM drivers take charge 227of the entire device, you can spot them with the DRIVER_MODESET flag. 228 229Unfortunately there's still large piles of legacy code around which needs to 230be hidden so that driver writers don't accidentally end up using it. And to 231prevent security issues in those legacy IOCTLs from being exploited on modern 232drivers. This has multiple possible subtasks: 233 234* Extract support code for legacy features into a ``drm-legacy.ko`` kernel 235 module and compile it only when one of the legacy drivers is enabled. 236 237This is mostly done, the only thing left is to split up ``drm_irq.c`` into 238legacy cruft and the parts needed by modern KMS drivers. 239 240Contact: Daniel Vetter 241 242Make panic handling work 243------------------------ 244 245This is a really varied tasks with lots of little bits and pieces: 246 247* The panic path can't be tested currently, leading to constant breaking. The 248 main issue here is that panics can be triggered from hardirq contexts and 249 hence all panic related callback can run in hardirq context. It would be 250 awesome if we could test at least the fbdev helper code and driver code by 251 e.g. trigger calls through drm debugfs files. hardirq context could be 252 achieved by using an IPI to the local processor. 253 254* There's a massive confusion of different panic handlers. DRM fbdev emulation 255 helpers have one, but on top of that the fbcon code itself also has one. We 256 need to make sure that they stop fighting over each another. 257 258* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 259 isn't a full solution for panic paths. We need to make sure that it only 260 returns true if there's a panic going on for real, and fix up all the 261 fallout. 262 263* The panic handler must never sleep, which also means it can't ever 264 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 265 even spinlocks (because NMI and hardirq can panic too). We need to either 266 make sure to not call such paths, or trylock everything. Really tricky. 267 268* For the above locking troubles reasons it's pretty much impossible to 269 attempt a synchronous modeset from panic handlers. The only thing we could 270 try to achive is an atomic ``set_base`` of the primary plane, and hope that 271 it shows up. Everything else probably needs to be delayed to some worker or 272 something else which happens later on. Otherwise it just kills the box 273 harder, prevent the panic from going out on e.g. netconsole. 274 275* There's also proposal for a simplied DRM console instead of the full-blown 276 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 277 obviously work for both console, in case we ever get kmslog merged. 278 279Contact: Daniel Vetter 280 281Clean up the debugfs support 282---------------------------- 283 284There's a bunch of issues with it: 285 286- The drm_info_list ->show() function doesn't even bother to cast to the drm 287 structure for you. This is lazy. 288 289- We probably want to have some support for debugfs files on crtc/connectors and 290 maybe other kms objects directly in core. There's even drm_print support in 291 the funcs for these objects to dump kms state, so it's all there. And then the 292 ->show() functions should obviously give you a pointer to the right object. 293 294- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 295 anything we want to print drm_device (or maybe drm_file) is the right thing. 296 297- The drm_driver->debugfs_init hooks we have is just an artifact of the old 298 midlayered load sequence. DRM debugfs should work more like sysfs, where you 299 can create properties/files for an object anytime you want, and the core 300 takes care of publishing/unpuplishing all the files at register/unregister 301 time. Drivers shouldn't need to worry about these technicalities, and fixing 302 this (together with the drm_minor->drm_device move) would allow us to remove 303 debugfs_init. 304 305Contact: Daniel Vetter 306 307KMS cleanups 308------------ 309 310Some of these date from the very introduction of KMS in 2008 ... 311 312- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should 313 be renamed to drm_mode_config.object_idr. 314 315- drm_display_mode doesn't need to be derived from drm_mode_object. That's 316 leftovers from older (never merged into upstream) KMS designs where modes 317 where set using their ID, including support to add/remove modes. 318 319Better Testing 320============== 321 322Enable trinity for DRM 323---------------------- 324 325And fix up the fallout. Should be really interesting ... 326 327Make KMS tests in i-g-t generic 328------------------------------- 329 330The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 331including tons of testcases for corner-cases in the modesetting API. It would 332be awesome if those tests (at least the ones not relying on Intel-specific GEM 333features) could be made to run on any KMS driver. 334 335Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 336converting things over. For modeset tests we also first need a bit of 337infrastructure to use dumb buffers for untiled buffers, to be able to run all 338the non-i915 specific modeset tests. 339 340Contact: Daniel Vetter 341 342Create a virtual KMS driver for testing (vkms) 343---------------------------------------------- 344 345With all the latest helpers it should be fairly simple to create a virtual KMS 346driver useful for testing, or for running X or similar on headless machines 347(to be able to still use the GPU). This would be similar to vgem, but aimed at 348the modeset side. 349 350Once the basics are there there's tons of possibilities to extend it. 351 352Contact: Daniel Vetter 353 354Driver Specific 355=============== 356 357tinydrm 358------- 359 360Tinydrm is the helper driver for really simple fb drivers. The goal is to make 361those drivers as simple as possible, so lots of room for refactoring: 362 363- backlight helpers, probably best to put them into a new drm_backlight.c. 364 This is because drivers/video is de-facto unmaintained. We could also 365 move drivers/video/backlight to drivers/gpu/backlight and take it all 366 over within drm-misc, but that's more work. Backlight helpers require a fair 367 bit of reworking and refactoring. A simple example is the enabling of a backlight. 368 Tinydrm has helpers for this. It would be good if other drivers can also use the 369 helper. However, there are various cases we need to consider i.e different 370 drivers seem to have different ways of enabling/disabling a backlight. 371 We also need to consider the backlight drivers (like gpio_backlight). The situation 372 is further complicated by the fact that the backlight is tied to fbdev 373 via fb_notifier_callback() which has complicated logic. For further details, refer 374 to the following discussion thread: 375 https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA 376 377- spi helpers, probably best put into spi core/helper code. Thierry said 378 the spi maintainer is fast&reactive, so shouldn't be a big issue. 379 380- extract the mipi-dbi helper (well, the non-tinydrm specific parts at 381 least) into a separate helper, like we have for mipi-dsi already. Or follow 382 one of the ideas for having a shared dsi/dbi helper, abstracting away the 383 transport details more. 384 385- tinydrm_lastclose could be drm_fb_helper_lastclose. Only thing we need 386 for that is to store the drm_fb_helper pointer somewhere in 387 drm_device->mode_config. And then we could roll that out to all the 388 drivers. 389 390- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma 391 helpers, as a _vmapped variant (since not every driver needs the vmap). 392 And tinydrm_gem_cma_free_object could the be merged into 393 drm_gem_cma_free_object(). 394 395- tinydrm_fb_create we could move into drm_simple_pipe, only need to add 396 the fb_create hook to drm_simple_pipe_funcs, which would again simplify a 397 bunch of things (since it gives you a one-stop vfunc for simple drivers). 398 399- Quick aside: The unregister devm stuff is kinda getting the lifetimes of 400 a drm_device wrong. Doesn't matter, since everyone else gets it wrong 401 too :-) 402 403- With the fbdev pointer in dev->mode_config we could also make 404 suspend/resume helpers entirely generic, at least if we add a 405 dev->mode_config.suspend_state. We could even provide a generic pm_ops 406 structure with those. 407 408- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above. 409 410Contact: Noralf Trønnes, Daniel Vetter 411 412AMD DC Display Driver 413--------------------- 414 415AMD DC is the display driver for AMD devices starting with Vega. There has been 416a bunch of progress cleaning it up but there's still plenty of work to be done. 417 418See drivers/gpu/drm/amd/display/TODO for tasks. 419 420Contact: Harry Wentland, Alex Deucher 421 422Outside DRM 423=========== 424