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 10Difficulty 11---------- 12 13To make it easier task are categorized into different levels: 14 15Starter: Good tasks to get started with the DRM subsystem. 16 17Intermediate: Tasks which need some experience with working in the DRM 18subsystem, or some specific GPU/display graphics knowledge. For debugging issue 19it's good to have the relevant hardware (or a virtual driver set up) available 20for testing. 21 22Advanced: Tricky tasks that need fairly good understanding of the DRM subsystem 23and graphics topics. Generally need the relevant hardware for development and 24testing. 25 26Expert: Only attempt these if you've successfully completed some tricky 27refactorings already and are an expert in the specific area 28 29Subsystem-wide refactorings 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instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Level: Intermediate 43 44Convert existing KMS drivers to atomic modesetting 45-------------------------------------------------- 46 473.19 has the atomic modeset interfaces and helpers, so drivers can now be 48converted over. Modern compositors like Wayland or Surfaceflinger on Android 49really want an atomic modeset interface, so this is all about the bright 50future. 51 52There is a conversion guide for atomic and all you need is a GPU for a 53non-converted driver (again virtual HW drivers for KVM are still all 54suitable). 55 56As part of this drivers also need to convert to universal plane (which means 57exposing primary & cursor as proper plane objects). But that's much easier to 58do by directly using the new atomic helper driver callbacks. 59 60Contact: Daniel Vetter, respective driver maintainers 61 62Level: Advanced 63 64Clean up the clipped coordination confusion around planes 65--------------------------------------------------------- 66 67We have a helper to get this right with drm_plane_helper_check_update(), but 68it's not consistently used. This should be fixed, preferrably in the atomic 69helpers (and drivers then moved over to clipped coordinates). Probably the 70helper should also be moved from drm_plane_helper.c to the atomic helpers, to 71avoid confusion - the other helpers in that file are all deprecated legacy 72helpers. 73 74Contact: Ville Syrjälä, Daniel Vetter, driver maintainers 75 76Level: Advanced 77 78Improve plane atomic_check helpers 79---------------------------------- 80 81Aside from the clipped coordinates right above there's a few suboptimal things 82with the current helpers: 83 84- drm_plane_helper_funcs->atomic_check gets called for enabled or disabled 85 planes. At best this seems to confuse drivers, worst it means they blow up 86 when the plane is disabled without the CRTC. The only special handling is 87 resetting values in the plane state structures, which instead should be moved 88 into the drm_plane_funcs->atomic_duplicate_state functions. 89 90- Once that's done, helpers could stop calling ->atomic_check for disabled 91 planes. 92 93- Then we could go through all the drivers and remove the more-or-less confused 94 checks for plane_state->fb and plane_state->crtc. 95 96Contact: Daniel Vetter 97 98Level: Advanced 99 100Convert early atomic drivers to async commit helpers 101---------------------------------------------------- 102 103For the first year the atomic modeset helpers didn't support asynchronous / 104nonblocking commits, and every driver had to hand-roll them. This is fixed 105now, but there's still a pile of existing drivers that easily could be 106converted over to the new infrastructure. 107 108One issue with the helpers is that they require that drivers handle completion 109events for atomic commits correctly. But fixing these bugs is good anyway. 110 111Somewhat related is the legacy_cursor_update hack, which should be replaced with 112the new atomic_async_check/commit functionality in the helpers in drivers that 113still look at that flag. 114 115Contact: Daniel Vetter, respective driver maintainers 116 117Level: Advanced 118 119Fallout from atomic KMS 120----------------------- 121 122``drm_atomic_helper.c`` provides a batch of functions which implement legacy 123IOCTLs on top of the new atomic driver interface. Which is really nice for 124gradual conversion of drivers, but unfortunately the semantic mismatches are 125a bit too severe. So there's some follow-up work to adjust the function 126interfaces to fix these issues: 127 128* atomic needs the lock acquire context. At the moment that's passed around 129 implicitly with some horrible hacks, and it's also allocate with 130 ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating 131 the acquire context explicitly on stack and then also pass it down into 132 drivers explicitly so that the legacy-on-atomic functions can use them. 133 134 Except for some driver code this is done. This task should be finished by 135 adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). 136 137* A bunch of the vtable hooks are now in the wrong place: DRM has a split 138 between core vfunc tables (named ``drm_foo_funcs``), which are used to 139 implement the userspace ABI. And then there's the optional hooks for the 140 helper libraries (name ``drm_foo_helper_funcs``), which are purely for 141 internal use. Some of these hooks should be move from ``_funcs`` to 142 ``_helper_funcs`` since they are not part of the core ABI. There's a 143 ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. 144 145Contact: Daniel Vetter 146 147Level: Intermediate 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 object ``free`` 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 only 168the ``msm`` and `i915` drivers use ``struct_mutex``. 169 170Contact: Daniel Vetter, respective driver maintainers 171 172Level: Advanced 173 174Move Buffer Object Locking to dma_resv_lock() 175--------------------------------------------- 176 177Many drivers have their own per-object locking scheme, usually using 178mutex_lock(). This causes all kinds of trouble for buffer sharing, since 179depending which driver is the exporter and importer, the locking hierarchy is 180reversed. 181 182To solve this we need one standard per-object locking mechanism, which is 183dma_resv_lock(). This lock needs to be called as the outermost lock, with all 184other driver specific per-object locks removed. The problem is tha rolling out 185the actual change to the locking contract is a flag day, due to struct dma_buf 186buffer sharing. 187 188Level: Expert 189 190Convert logging to drm_* functions with drm_device paramater 191------------------------------------------------------------ 192 193For drivers which could have multiple instances, it is necessary to 194differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR 195don't do this, drivers used dev_info/warn/err to make this differentiation. We 196now have drm_* variants of the drm print functions, so we can start to convert 197those drivers back to using drm-formatted specific log messages. 198 199Before you start this conversion please contact the relevant maintainers to make 200sure your work will be merged - not everyone agrees that the DRM dmesg macros 201are better. 202 203Contact: Sean Paul, Maintainer of the driver you plan to convert 204 205Level: Starter 206 207Convert drivers to use simple modeset suspend/resume 208---------------------------------------------------- 209 210Most drivers (except i915 and nouveau) that use 211drm_atomic_helper_suspend/resume() can probably be converted to use 212drm_mode_config_helper_suspend/resume(). Also there's still open-coded version 213of the atomic suspend/resume code in older atomic modeset drivers. 214 215Contact: Maintainer of the driver you plan to convert 216 217Level: Intermediate 218 219Convert drivers to use drm_fbdev_generic_setup() 220------------------------------------------------ 221 222Most drivers can use drm_fbdev_generic_setup(). Driver have to implement 223atomic modesetting and GEM vmap support. Historically, generic fbdev emulation 224expected the framebuffer in system memory or system-like memory. By employing 225struct dma_buf_map, drivers with frambuffers in I/O memory can be supported 226as well. 227 228Contact: Maintainer of the driver you plan to convert 229 230Level: Intermediate 231 232Reimplement functions in drm_fbdev_fb_ops without fbdev 233------------------------------------------------------- 234 235A number of callback functions in drm_fbdev_fb_ops could benefit from 236being rewritten without dependencies on the fbdev module. Some of the 237helpers could further benefit from using struct dma_buf_map instead of 238raw pointers. 239 240Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 241 242Level: Advanced 243 244 245drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup 246----------------------------------------------------------------- 247 248A lot more drivers could be switched over to the drm_gem_framebuffer helpers. 249Various hold-ups: 250 251- Need to switch over to the generic dirty tracking code using 252 drm_atomic_helper_dirtyfb first (e.g. qxl). 253 254- Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb 255 setup code can't be deleted. 256 257- Many drivers wrap drm_gem_fb_create() only to check for valid formats. For 258 atomic drivers we could check for valid formats by calling 259 drm_plane_check_pixel_format() against all planes, and pass if any plane 260 supports the format. For non-atomic that's not possible since like the format 261 list for the primary plane is fake and we'd therefor reject valid formats. 262 263- Many drivers subclass drm_framebuffer, we'd need a embedding compatible 264 version of the varios drm_gem_fb_create functions. Maybe called 265 drm_gem_fb_create/_with_dirty/_with_funcs as needed. 266 267Contact: Daniel Vetter 268 269Level: Intermediate 270 271Clean up mmap forwarding 272------------------------ 273 274A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers. 275And also a lot of them forward dma-buf mmap to the gem mmap implementations. 276There's drm_gem_prime_mmap() for this now, but still needs to be rolled out. 277 278Contact: Daniel Vetter 279 280Level: Intermediate 281 282Generic fbdev defio support 283--------------------------- 284 285The defio support code in the fbdev core has some very specific requirements, 286which means drivers need to have a special framebuffer for fbdev. The main 287issue is that it uses some fields in struct page itself, which breaks shmem 288gem objects (and other things). To support defio, affected drivers require 289the use of a shadow buffer, which may add CPU and memory overhead. 290 291Possible solution would be to write our own defio mmap code in the drm fbdev 292emulation. It would need to fully wrap the existing mmap ops, forwarding 293everything after it has done the write-protect/mkwrite trickery: 294 295- In the drm_fbdev_fb_mmap helper, if we need defio, change the 296 default page prots to write-protected with something like this:: 297 298 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 299 300- Set the mkwrite and fsync callbacks with similar implementions to the core 301 fbdev defio stuff. These should all work on plain ptes, they don't actually 302 require a struct page. uff. These should all work on plain ptes, they don't 303 actually require a struct page. 304 305- Track the dirty pages in a separate structure (bitfield with one bit per page 306 should work) to avoid clobbering struct page. 307 308Might be good to also have some igt testcases for this. 309 310Contact: Daniel Vetter, Noralf Tronnes 311 312Level: Advanced 313 314Garbage collect fbdev scrolling acceleration 315-------------------------------------------- 316 317Scroll acceleration is disabled in fbcon by hard-wiring p->scrollmode = 318SCROLL_REDRAW. There's a ton of code this will allow us to remove: 319 320- lots of code in fbcon.c 321 322- a bunch of the hooks in fbcon_ops, maybe the remaining hooks could be called 323 directly instead of the function table (with a switch on p->rotate) 324 325- fb_copyarea is unused after this, and can be deleted from all drivers 326 327Note that not all acceleration code can be deleted, since clearing and cursor 328support is still accelerated, which might be good candidates for further 329deletion projects. 330 331Contact: Daniel Vetter 332 333Level: Intermediate 334 335idr_init_base() 336--------------- 337 338DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 339userspace IDs to internal objects, and in most places ID=0 means NULL and hence 340is never used. Switching to idr_init_base() for these would make the idr more 341efficient. 342 343Contact: Daniel Vetter 344 345Level: Starter 346 347struct drm_gem_object_funcs 348--------------------------- 349 350GEM objects can now have a function table instead of having the callbacks on the 351DRM driver struct. This is now the preferred way. Callbacks in drivers have been 352converted, except for struct drm_driver.gem_prime_mmap. 353 354Level: Intermediate 355 356Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate 357--------------------------------------------------------- 358 359For cases where drivers are attempting to grab the modeset locks with a local 360acquire context. Replace the boilerplate code surrounding 361drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and 362DRM_MODESET_LOCK_ALL_END() instead. 363 364This should also be done for all places where drm_modeset_lock_all() is still 365used. 366 367As a reference, take a look at the conversions already completed in drm core. 368 369Contact: Sean Paul, respective driver maintainers 370 371Level: Starter 372 373Rename CMA helpers to DMA helpers 374--------------------------------- 375 376CMA (standing for contiguous memory allocator) is really a bit an accident of 377what these were used for first, a much better name would be DMA helpers. In the 378text these should even be called coherent DMA memory helpers (so maybe CDM, but 379no one knows what that means) since underneath they just use dma_alloc_coherent. 380 381Contact: Laurent Pinchart, Daniel Vetter 382 383Level: Intermediate (mostly because it is a huge tasks without good partial 384milestones, not technically itself that challenging) 385 386connector register/unregister fixes 387----------------------------------- 388 389- For most connectors it's a no-op to call drm_connector_register/unregister 390 directly from driver code, drm_dev_register/unregister take care of this 391 already. We can remove all of them. 392 393- For dp drivers it's a bit more a mess, since we need the connector to be 394 registered when calling drm_dp_aux_register. Fix this by instead calling 395 drm_dp_aux_init, and moving the actual registering into a late_register 396 callback as recommended in the kerneldoc. 397 398Level: Intermediate 399 400Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 401--------------------------------------------------------------- 402 403The load/unload callbacks in struct &drm_driver are very much midlayers, plus 404for historical reasons they get the ordering wrong (and we can't fix that) 405between setting up the &drm_driver structure and calling drm_dev_register(). 406 407- Rework drivers to no longer use the load/unload callbacks, directly coding the 408 load/unload sequence into the driver's probe function. 409 410- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 411 callbacks for all modern drivers. 412 413Contact: Daniel Vetter 414 415Level: Intermediate 416 417Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 418--------------------------------------------------------------- 419 420Once EDID is parsed, the monitor HDMI support information is available through 421drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 422retrieve the same information, which is less efficient. 423 424Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 425drm_display_info.is_hdmi if applicable. 426 427Contact: Laurent Pinchart, respective driver maintainers 428 429Level: Intermediate 430 431Consolidate custom driver modeset properties 432-------------------------------------------- 433 434Before atomic modeset took place, many drivers where creating their own 435properties. Among other things, atomic brought the requirement that custom, 436driver specific properties should not be used. 437 438For this task, we aim to introduce core helpers or reuse the existing ones 439if available: 440 441A quick, unconfirmed, examples list. 442 443Introduce core helpers: 444- audio (amdgpu, intel, gma500, radeon) 445- brightness, contrast, etc (armada, nouveau) - overlay only (?) 446- broadcast rgb (gma500, intel) 447- colorkey (armada, nouveau, rcar) - overlay only (?) 448- dither (amdgpu, nouveau, radeon) - varies across drivers 449- underscan family (amdgpu, radeon, nouveau) 450 451Already in core: 452- colorspace (sti) 453- tv format names, enhancements (gma500, intel) 454- tv overscan, margins, etc. (gma500, intel) 455- zorder (omapdrm) - same as zpos (?) 456 457 458Contact: Emil Velikov, respective driver maintainers 459 460Level: Intermediate 461 462Use struct dma_buf_map throughout codebase 463------------------------------------------ 464 465Pointers to shared device memory are stored in struct dma_buf_map. Each 466instance knows whether it refers to system or I/O memory. Most of the DRM-wide 467interface have been converted to use struct dma_buf_map, but implementations 468often still use raw pointers. 469 470The task is to use struct dma_buf_map where it makes sense. 471 472* Memory managers should use struct dma_buf_map for dma-buf-imported buffers. 473* TTM might benefit from using struct dma_buf_map internally. 474* Framebuffer copying and blitting helpers should operate on struct dma_buf_map. 475 476Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Daniel Vetter 477 478Level: Intermediate 479 480 481Core refactorings 482================= 483 484Make panic handling work 485------------------------ 486 487This is a really varied tasks with lots of little bits and pieces: 488 489* The panic path can't be tested currently, leading to constant breaking. The 490 main issue here is that panics can be triggered from hardirq contexts and 491 hence all panic related callback can run in hardirq context. It would be 492 awesome if we could test at least the fbdev helper code and driver code by 493 e.g. trigger calls through drm debugfs files. hardirq context could be 494 achieved by using an IPI to the local processor. 495 496* There's a massive confusion of different panic handlers. DRM fbdev emulation 497 helpers have one, but on top of that the fbcon code itself also has one. We 498 need to make sure that they stop fighting over each another. 499 500* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 501 isn't a full solution for panic paths. We need to make sure that it only 502 returns true if there's a panic going on for real, and fix up all the 503 fallout. 504 505* The panic handler must never sleep, which also means it can't ever 506 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 507 even spinlocks (because NMI and hardirq can panic too). We need to either 508 make sure to not call such paths, or trylock everything. Really tricky. 509 510* For the above locking troubles reasons it's pretty much impossible to 511 attempt a synchronous modeset from panic handlers. The only thing we could 512 try to achive is an atomic ``set_base`` of the primary plane, and hope that 513 it shows up. Everything else probably needs to be delayed to some worker or 514 something else which happens later on. Otherwise it just kills the box 515 harder, prevent the panic from going out on e.g. netconsole. 516 517* There's also proposal for a simplied DRM console instead of the full-blown 518 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 519 obviously work for both console, in case we ever get kmslog merged. 520 521Contact: Daniel Vetter 522 523Level: Advanced 524 525Clean up the debugfs support 526---------------------------- 527 528There's a bunch of issues with it: 529 530- The drm_info_list ->show() function doesn't even bother to cast to the drm 531 structure for you. This is lazy. 532 533- We probably want to have some support for debugfs files on crtc/connectors and 534 maybe other kms objects directly in core. There's even drm_print support in 535 the funcs for these objects to dump kms state, so it's all there. And then the 536 ->show() functions should obviously give you a pointer to the right object. 537 538- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 539 anything we want to print drm_device (or maybe drm_file) is the right thing. 540 541- The drm_driver->debugfs_init hooks we have is just an artifact of the old 542 midlayered load sequence. DRM debugfs should work more like sysfs, where you 543 can create properties/files for an object anytime you want, and the core 544 takes care of publishing/unpuplishing all the files at register/unregister 545 time. Drivers shouldn't need to worry about these technicalities, and fixing 546 this (together with the drm_minor->drm_device move) would allow us to remove 547 debugfs_init. 548 549Previous RFC that hasn't landed yet: https://lore.kernel.org/dri-devel/20200513114130.28641-2-wambui.karugax@gmail.com/ 550 551Contact: Daniel Vetter 552 553Level: Intermediate 554 555Object lifetime fixes 556--------------------- 557 558There's two related issues here 559 560- Cleanup up the various ->destroy callbacks, which often are all the same 561 simple code. 562 563- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, 564 which results in use-after free issues on driver unload. This can be serious 565 trouble even for drivers for hardware integrated on the SoC due to 566 EPROBE_DEFERRED backoff. 567 568Both these problems can be solved by switching over to drmm_kzalloc(), and the 569various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), 570drmm_universal_plane_alloc(), ... and so on. 571 572Contact: Daniel Vetter 573 574Level: Intermediate 575 576Remove automatic page mapping from dma-buf importing 577---------------------------------------------------- 578 579When importing dma-bufs, the dma-buf and PRIME frameworks automatically map 580imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and 581drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() 582even if they never do actual device DMA, but only CPU access through 583dma_buf_vmap(). This is a problem for USB devices, which do not support DMA 584operations. 585 586To fix the issue, automatic page mappings should be removed from the 587buffer-sharing code. Fixing this is a bit more involved, since the import/export 588cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over 589this problem for USB devices by fishing out the USB host controller device, as 590long as that supports DMA. Otherwise importing can still needlessly fail. 591 592Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 593 594Level: Advanced 595 596 597Better Testing 598============== 599 600Enable trinity for DRM 601---------------------- 602 603And fix up the fallout. Should be really interesting ... 604 605Level: Advanced 606 607Make KMS tests in i-g-t generic 608------------------------------- 609 610The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 611including tons of testcases for corner-cases in the modesetting API. It would 612be awesome if those tests (at least the ones not relying on Intel-specific GEM 613features) could be made to run on any KMS driver. 614 615Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 616converting things over. For modeset tests we also first need a bit of 617infrastructure to use dumb buffers for untiled buffers, to be able to run all 618the non-i915 specific modeset tests. 619 620Level: Advanced 621 622Extend virtual test driver (VKMS) 623--------------------------------- 624 625See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 626internship task, since it only requires a virtual machine and can be sized to 627fit the available time. 628 629Level: See details 630 631Backlight Refactoring 632--------------------- 633 634Backlight drivers have a triple enable/disable state, which is a bit overkill. 635Plan to fix this: 636 6371. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 638 has started already. 6392. In all, only look at one of the three status bits set by the above helpers. 6403. Remove the other two status bits. 641 642Contact: Daniel Vetter 643 644Level: Intermediate 645 646Driver Specific 647=============== 648 649AMD DC Display Driver 650--------------------- 651 652AMD DC is the display driver for AMD devices starting with Vega. There has been 653a bunch of progress cleaning it up but there's still plenty of work to be done. 654 655See drivers/gpu/drm/amd/display/TODO for tasks. 656 657Contact: Harry Wentland, Alex Deucher 658 659Bootsplash 660========== 661 662There is support in place now for writing internal DRM clients making it 663possible to pick up the bootsplash work that was rejected because it was written 664for fbdev. 665 666- [v6,8/8] drm/client: Hack: Add bootsplash example 667 https://patchwork.freedesktop.org/patch/306579/ 668 669- [RFC PATCH v2 00/13] Kernel based bootsplash 670 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de 671 672Contact: Sam Ravnborg 673 674Level: Advanced 675 676Outside DRM 677=========== 678 679Convert fbdev drivers to DRM 680---------------------------- 681 682There are plenty of fbdev drivers for older hardware. Some hardware has 683become obsolete, but some still provides good(-enough) framebuffers. The 684drivers that are still useful should be converted to DRM and afterwards 685removed from fbdev. 686 687Very simple fbdev drivers can best be converted by starting with a new 688DRM driver. Simple KMS helpers and SHMEM should be able to handle any 689existing hardware. The new driver's call-back functions are filled from 690existing fbdev code. 691 692More complex fbdev drivers can be refactored step-by-step into a DRM 693driver with the help of the DRM fbconv helpers. [1] These helpers provide 694the transition layer between the DRM core infrastructure and the fbdev 695driver interface. Create a new DRM driver on top of the fbconv helpers, 696copy over the fbdev driver, and hook it up to the DRM code. Examples for 697several fbdev drivers are available at [1] and a tutorial of this process 698available at [2]. The result is a primitive DRM driver that can run X11 699and Weston. 700 701 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 702 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 703 704Contact: Thomas Zimmermann <tzimmermann@suse.de> 705 706Level: Advanced 707