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instead. 36Audit each individual driver, make sure it'll work with the generic 37implementation (there's lots of outdated locking leftovers in various 38implementations), and then remove it. 39 40Contact: Daniel Vetter, respective driver maintainers 41 42Level: Intermediate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 271Generic fbdev defio support 272--------------------------- 273 274The defio support code in the fbdev core has some very specific requirements, 275which means drivers need to have a special framebuffer for fbdev. The main 276issue is that it uses some fields in struct page itself, which breaks shmem 277gem objects (and other things). To support defio, affected drivers require 278the use of a shadow buffer, which may add CPU and memory overhead. 279 280Possible solution would be to write our own defio mmap code in the drm fbdev 281emulation. It would need to fully wrap the existing mmap ops, forwarding 282everything after it has done the write-protect/mkwrite trickery: 283 284- In the drm_fbdev_fb_mmap helper, if we need defio, change the 285 default page prots to write-protected with something like this:: 286 287 vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); 288 289- Set the mkwrite and fsync callbacks with similar implementions to the core 290 fbdev defio stuff. These should all work on plain ptes, they don't actually 291 require a struct page. uff. These should all work on plain ptes, they don't 292 actually require a struct page. 293 294- Track the dirty pages in a separate structure (bitfield with one bit per page 295 should work) to avoid clobbering struct page. 296 297Might be good to also have some igt testcases for this. 298 299Contact: Daniel Vetter, Noralf Tronnes 300 301Level: Advanced 302 303Garbage collect fbdev scrolling acceleration 304-------------------------------------------- 305 306Scroll acceleration has been disabled in fbcon. Now it works as the old 307SCROLL_REDRAW mode. A ton of code was removed in fbcon.c and the hook bmove was 308removed from fbcon_ops. 309Remaining tasks: 310 311- a bunch of the hooks in fbcon_ops could be removed or simplified by calling 312 directly instead of the function table (with a switch on p->rotate) 313 314- fb_copyarea is unused after this, and can be deleted from all drivers 315 316- after that, fb_copyarea can be deleted from fb_ops in include/linux/fb.h as 317 well as cfb_copyarea 318 319Note that not all acceleration code can be deleted, since clearing and cursor 320support is still accelerated, which might be good candidates for further 321deletion projects. 322 323Contact: Daniel Vetter 324 325Level: Intermediate 326 327idr_init_base() 328--------------- 329 330DRM core&drivers uses a lot of idr (integer lookup directories) for mapping 331userspace IDs to internal objects, and in most places ID=0 means NULL and hence 332is never used. Switching to idr_init_base() for these would make the idr more 333efficient. 334 335Contact: Daniel Vetter 336 337Level: Starter 338 339struct drm_gem_object_funcs 340--------------------------- 341 342GEM objects can now have a function table instead of having the callbacks on the 343DRM driver struct. This is now the preferred way. Callbacks in drivers have been 344converted, except for struct drm_driver.gem_prime_mmap. 345 346Level: Intermediate 347 348Rename CMA helpers to DMA helpers 349--------------------------------- 350 351CMA (standing for contiguous memory allocator) is really a bit an accident of 352what these were used for first, a much better name would be DMA helpers. In the 353text these should even be called coherent DMA memory helpers (so maybe CDM, but 354no one knows what that means) since underneath they just use dma_alloc_coherent. 355 356Contact: Laurent Pinchart, Daniel Vetter 357 358Level: Intermediate (mostly because it is a huge tasks without good partial 359milestones, not technically itself that challenging) 360 361connector register/unregister fixes 362----------------------------------- 363 364- For most connectors it's a no-op to call drm_connector_register/unregister 365 directly from driver code, drm_dev_register/unregister take care of this 366 already. We can remove all of them. 367 368- For dp drivers it's a bit more a mess, since we need the connector to be 369 registered when calling drm_dp_aux_register. Fix this by instead calling 370 drm_dp_aux_init, and moving the actual registering into a late_register 371 callback as recommended in the kerneldoc. 372 373Level: Intermediate 374 375Remove load/unload callbacks from all non-DRIVER_LEGACY drivers 376--------------------------------------------------------------- 377 378The load/unload callbacks in struct &drm_driver are very much midlayers, plus 379for historical reasons they get the ordering wrong (and we can't fix that) 380between setting up the &drm_driver structure and calling drm_dev_register(). 381 382- Rework drivers to no longer use the load/unload callbacks, directly coding the 383 load/unload sequence into the driver's probe function. 384 385- Once all non-DRIVER_LEGACY drivers are converted, disallow the load/unload 386 callbacks for all modern drivers. 387 388Contact: Daniel Vetter 389 390Level: Intermediate 391 392Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi 393--------------------------------------------------------------- 394 395Once EDID is parsed, the monitor HDMI support information is available through 396drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to 397retrieve the same information, which is less efficient. 398 399Audit each individual driver calling drm_detect_hdmi_monitor() and switch to 400drm_display_info.is_hdmi if applicable. 401 402Contact: Laurent Pinchart, respective driver maintainers 403 404Level: Intermediate 405 406Consolidate custom driver modeset properties 407-------------------------------------------- 408 409Before atomic modeset took place, many drivers where creating their own 410properties. Among other things, atomic brought the requirement that custom, 411driver specific properties should not be used. 412 413For this task, we aim to introduce core helpers or reuse the existing ones 414if available: 415 416A quick, unconfirmed, examples list. 417 418Introduce core helpers: 419- audio (amdgpu, intel, gma500, radeon) 420- brightness, contrast, etc (armada, nouveau) - overlay only (?) 421- broadcast rgb (gma500, intel) 422- colorkey (armada, nouveau, rcar) - overlay only (?) 423- dither (amdgpu, nouveau, radeon) - varies across drivers 424- underscan family (amdgpu, radeon, nouveau) 425 426Already in core: 427- colorspace (sti) 428- tv format names, enhancements (gma500, intel) 429- tv overscan, margins, etc. (gma500, intel) 430- zorder (omapdrm) - same as zpos (?) 431 432 433Contact: Emil Velikov, respective driver maintainers 434 435Level: Intermediate 436 437Use struct dma_buf_map throughout codebase 438------------------------------------------ 439 440Pointers to shared device memory are stored in struct dma_buf_map. Each 441instance knows whether it refers to system or I/O memory. Most of the DRM-wide 442interface have been converted to use struct dma_buf_map, but implementations 443often still use raw pointers. 444 445The task is to use struct dma_buf_map where it makes sense. 446 447* Memory managers should use struct dma_buf_map for dma-buf-imported buffers. 448* TTM might benefit from using struct dma_buf_map internally. 449* Framebuffer copying and blitting helpers should operate on struct dma_buf_map. 450 451Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Daniel Vetter 452 453Level: Intermediate 454 455Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly 456-------------------------------------------------------------------------------------- 457 458The values in struct drm_mode_config.{max_width,max_height} describe the 459maximum supported framebuffer size. It's the virtual screen size, but many 460drivers treat it like limitations of the physical resolution. 461 462The maximum width depends on the hardware's maximum scanline pitch. The 463maximum height depends on the amount of addressable video memory. Review all 464drivers to initialize the fields to the correct values. 465 466Contact: Thomas Zimmermann <tzimmermann@suse.de> 467 468Level: Intermediate 469 470 471Core refactorings 472================= 473 474Make panic handling work 475------------------------ 476 477This is a really varied tasks with lots of little bits and pieces: 478 479* The panic path can't be tested currently, leading to constant breaking. The 480 main issue here is that panics can be triggered from hardirq contexts and 481 hence all panic related callback can run in hardirq context. It would be 482 awesome if we could test at least the fbdev helper code and driver code by 483 e.g. trigger calls through drm debugfs files. hardirq context could be 484 achieved by using an IPI to the local processor. 485 486* There's a massive confusion of different panic handlers. DRM fbdev emulation 487 helpers have one, but on top of that the fbcon code itself also has one. We 488 need to make sure that they stop fighting over each another. 489 490* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and 491 isn't a full solution for panic paths. We need to make sure that it only 492 returns true if there's a panic going on for real, and fix up all the 493 fallout. 494 495* The panic handler must never sleep, which also means it can't ever 496 ``mutex_lock()``. Also it can't grab any other lock unconditionally, not 497 even spinlocks (because NMI and hardirq can panic too). We need to either 498 make sure to not call such paths, or trylock everything. Really tricky. 499 500* For the above locking troubles reasons it's pretty much impossible to 501 attempt a synchronous modeset from panic handlers. The only thing we could 502 try to achive is an atomic ``set_base`` of the primary plane, and hope that 503 it shows up. Everything else probably needs to be delayed to some worker or 504 something else which happens later on. Otherwise it just kills the box 505 harder, prevent the panic from going out on e.g. netconsole. 506 507* There's also proposal for a simplied DRM console instead of the full-blown 508 fbcon and DRM fbdev emulation. Any kind of panic handling tricks should 509 obviously work for both console, in case we ever get kmslog merged. 510 511Contact: Daniel Vetter 512 513Level: Advanced 514 515Clean up the debugfs support 516---------------------------- 517 518There's a bunch of issues with it: 519 520- The drm_info_list ->show() function doesn't even bother to cast to the drm 521 structure for you. This is lazy. 522 523- We probably want to have some support for debugfs files on crtc/connectors and 524 maybe other kms objects directly in core. There's even drm_print support in 525 the funcs for these objects to dump kms state, so it's all there. And then the 526 ->show() functions should obviously give you a pointer to the right object. 527 528- The drm_info_list stuff is centered on drm_minor instead of drm_device. For 529 anything we want to print drm_device (or maybe drm_file) is the right thing. 530 531- The drm_driver->debugfs_init hooks we have is just an artifact of the old 532 midlayered load sequence. DRM debugfs should work more like sysfs, where you 533 can create properties/files for an object anytime you want, and the core 534 takes care of publishing/unpuplishing all the files at register/unregister 535 time. Drivers shouldn't need to worry about these technicalities, and fixing 536 this (together with the drm_minor->drm_device move) would allow us to remove 537 debugfs_init. 538 539Previous RFC that hasn't landed yet: https://lore.kernel.org/dri-devel/20200513114130.28641-2-wambui.karugax@gmail.com/ 540 541Contact: Daniel Vetter 542 543Level: Intermediate 544 545Object lifetime fixes 546--------------------- 547 548There's two related issues here 549 550- Cleanup up the various ->destroy callbacks, which often are all the same 551 simple code. 552 553- Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, 554 which results in use-after free issues on driver unload. This can be serious 555 trouble even for drivers for hardware integrated on the SoC due to 556 EPROBE_DEFERRED backoff. 557 558Both these problems can be solved by switching over to drmm_kzalloc(), and the 559various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), 560drmm_universal_plane_alloc(), ... and so on. 561 562Contact: Daniel Vetter 563 564Level: Intermediate 565 566Remove automatic page mapping from dma-buf importing 567---------------------------------------------------- 568 569When importing dma-bufs, the dma-buf and PRIME frameworks automatically map 570imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and 571drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() 572even if they never do actual device DMA, but only CPU access through 573dma_buf_vmap(). This is a problem for USB devices, which do not support DMA 574operations. 575 576To fix the issue, automatic page mappings should be removed from the 577buffer-sharing code. Fixing this is a bit more involved, since the import/export 578cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over 579this problem for USB devices by fishing out the USB host controller device, as 580long as that supports DMA. Otherwise importing can still needlessly fail. 581 582Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter 583 584Level: Advanced 585 586 587Better Testing 588============== 589 590Enable trinity for DRM 591---------------------- 592 593And fix up the fallout. Should be really interesting ... 594 595Level: Advanced 596 597Make KMS tests in i-g-t generic 598------------------------------- 599 600The i915 driver team maintains an extensive testsuite for the i915 DRM driver, 601including tons of testcases for corner-cases in the modesetting API. It would 602be awesome if those tests (at least the ones not relying on Intel-specific GEM 603features) could be made to run on any KMS driver. 604 605Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- 606converting things over. For modeset tests we also first need a bit of 607infrastructure to use dumb buffers for untiled buffers, to be able to run all 608the non-i915 specific modeset tests. 609 610Level: Advanced 611 612Extend virtual test driver (VKMS) 613--------------------------------- 614 615See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal 616internship task, since it only requires a virtual machine and can be sized to 617fit the available time. 618 619Level: See details 620 621Backlight Refactoring 622--------------------- 623 624Backlight drivers have a triple enable/disable state, which is a bit overkill. 625Plan to fix this: 626 6271. Roll out backlight_enable() and backlight_disable() helpers everywhere. This 628 has started already. 6292. In all, only look at one of the three status bits set by the above helpers. 6303. Remove the other two status bits. 631 632Contact: Daniel Vetter 633 634Level: Intermediate 635 636Driver Specific 637=============== 638 639AMD DC Display Driver 640--------------------- 641 642AMD DC is the display driver for AMD devices starting with Vega. There has been 643a bunch of progress cleaning it up but there's still plenty of work to be done. 644 645See drivers/gpu/drm/amd/display/TODO for tasks. 646 647Contact: Harry Wentland, Alex Deucher 648 649vmwgfx: Replace hashtable with Linux' implementation 650---------------------------------------------------- 651 652The vmwgfx driver uses its own hashtable implementation. Replace the 653code with Linux' implementation and update the callers. It's mostly a 654refactoring task, but the interfaces are different. 655 656Contact: Zack Rusin, Thomas Zimmermann <tzimmermann@suse.de> 657 658Level: Intermediate 659 660Bootsplash 661========== 662 663There is support in place now for writing internal DRM clients making it 664possible to pick up the bootsplash work that was rejected because it was written 665for fbdev. 666 667- [v6,8/8] drm/client: Hack: Add bootsplash example 668 https://patchwork.freedesktop.org/patch/306579/ 669 670- [RFC PATCH v2 00/13] Kernel based bootsplash 671 https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de 672 673Contact: Sam Ravnborg 674 675Level: Advanced 676 677Outside DRM 678=========== 679 680Convert fbdev drivers to DRM 681---------------------------- 682 683There are plenty of fbdev drivers for older hardware. Some hardware has 684become obsolete, but some still provides good(-enough) framebuffers. The 685drivers that are still useful should be converted to DRM and afterwards 686removed from fbdev. 687 688Very simple fbdev drivers can best be converted by starting with a new 689DRM driver. Simple KMS helpers and SHMEM should be able to handle any 690existing hardware. The new driver's call-back functions are filled from 691existing fbdev code. 692 693More complex fbdev drivers can be refactored step-by-step into a DRM 694driver with the help of the DRM fbconv helpers. [1] These helpers provide 695the transition layer between the DRM core infrastructure and the fbdev 696driver interface. Create a new DRM driver on top of the fbconv helpers, 697copy over the fbdev driver, and hook it up to the DRM code. Examples for 698several fbdev drivers are available at [1] and a tutorial of this process 699available at [2]. The result is a primitive DRM driver that can run X11 700and Weston. 701 702 - [1] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv 703 - [2] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c 704 705Contact: Thomas Zimmermann <tzimmermann@suse.de> 706 707Level: Advanced 708