Documentation/gpu/todo.rst - third_party/linux - Git at Google

 .. _todo:

 =========
 TODO list
 =========

 This section contains a list of smaller janitorial tasks in the kernel DRM
 graphics subsystem useful as newbie projects. Or for slow rainy days.

 Subsystem-wide refactorings
 ===========================

 Remove custom dumb_map_offset implementations
 ---------------------------------------------

 All GEM based drivers should be using drm_gem_create_mmap_offset() instead.
 Audit each individual driver, make sure it'll work with the generic
 implementation (there's lots of outdated locking leftovers in various
 implementations), and then remove it.

 Contact: Daniel Vetter, respective driver maintainers

 Convert existing KMS drivers to atomic modesetting
 --------------------------------------------------

 3.19 has the atomic modeset interfaces and helpers, so drivers can now be
 converted over. Modern compositors like Wayland or Surfaceflinger on Android
 really want an atomic modeset interface, so this is all about the bright
 future.

 There is a conversion guide for atomic and all you need is a GPU for a
 non-converted driver (again virtual HW drivers for KVM are still all
 suitable).

 As part of this drivers also need to convert to universal plane (which means
 exposing primary & cursor as proper plane objects). But that's much easier to
 do by directly using the new atomic helper driver callbacks.

 Contact: Daniel Vetter, respective driver maintainers

 Clean up the clipped coordination confusion around planes
 ---------------------------------------------------------

 We have a helper to get this right with drm_plane_helper_check_update(), but
 it's not consistently used. This should be fixed, preferrably in the atomic
 helpers (and drivers then moved over to clipped coordinates). Probably the
 helper should also be moved from drm_plane_helper.c to the atomic helpers, to
 avoid confusion - the other helpers in that file are all deprecated legacy
 helpers.

 Contact: Ville Syrjälä, Daniel Vetter, driver maintainers

 Convert early atomic drivers to async commit helpers
 ----------------------------------------------------

 For the first year the atomic modeset helpers didn't support asynchronous /
 nonblocking commits, and every driver had to hand-roll them. This is fixed
 now, but there's still a pile of existing drivers that easily could be
 converted over to the new infrastructure.

 One issue with the helpers is that they require that drivers handle completion
 events for atomic commits correctly. But fixing these bugs is good anyway.

 Contact: Daniel Vetter, respective driver maintainers

 Fallout from atomic KMS
 -----------------------

 ``drm_atomic_helper.c`` provides a batch of functions which implement legacy
 IOCTLs on top of the new atomic driver interface. Which is really nice for
 gradual conversion of drivers, but unfortunately the semantic mismatches are
 a bit too severe. So there's some follow-up work to adjust the function
 interfaces to fix these issues:

 * atomic needs the lock acquire context. At the moment that's passed around
   implicitly with some horrible hacks, and it's also allocate with
   ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
   the acquire context explicitly on stack and then also pass it down into
   drivers explicitly so that the legacy-on-atomic functions can use them.

   Except for some driver code this is done. This task should be finished by
   adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().

 * A bunch of the vtable hooks are now in the wrong place: DRM has a split
   between core vfunc tables (named ``drm_foo_funcs``), which are used to
   implement the userspace ABI. And then there's the optional hooks for the
   helper libraries (name ``drm_foo_helper_funcs``), which are purely for
   internal use. Some of these hooks should be move from ``_funcs`` to
   ``_helper_funcs`` since they are not part of the core ABI. There's a
   ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.

 Contact: Daniel Vetter

 Get rid of dev->struct_mutex from GEM drivers
 ---------------------------------------------

 ``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
 everything. Nowadays in modern drivers the only bit where it's mandatory is
 serializing GEM buffer object destruction. Which unfortunately means drivers
 have to keep track of that lock and either call ``unreference`` or
 ``unreference_locked`` depending upon context.

 Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
 and there's a ``gem_free_object_unlocked`` callback for any drivers which are
 entirely ``struct_mutex`` free.

 For drivers that need ``struct_mutex`` it should be replaced with a driver-
 private lock. The tricky part is the BO free functions, since those can't
 reliably take that lock any more. Instead state needs to be protected with
 suitable subordinate locks or some cleanup work pushed to a worker thread. For
 performance-critical drivers it might also be better to go with a more
 fine-grained per-buffer object and per-context lockings scheme. Currently only the
 ``msm`` driver still use ``struct_mutex``.

 Contact: Daniel Vetter, respective driver maintainers

 Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent
 ----------------------------------------------------------------------------

 For drivers which could have multiple instances, it is necessary to
 differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
 don't do this, drivers used dev_info/warn/err to make this differentiation. We
 now have DRM_DEV_* variants of the drm print macros, so we can start to convert
 those drivers back to using drm-formwatted specific log messages.

 Before you start this conversion please contact the relevant maintainers to make
 sure your work will be merged - not everyone agrees that the DRM dmesg macros
 are better.

 Contact: Sean Paul, Maintainer of the driver you plan to convert

 Convert drivers to use simple modeset suspend/resume
 ----------------------------------------------------

 Most drivers (except i915 and nouveau) that use
 drm_atomic_helper_suspend/resume() can probably be converted to use
 drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
 of the atomic suspend/resume code in older atomic modeset drivers.

 Contact: Maintainer of the driver you plan to convert

 Convert drivers to use drm_fb_helper_fbdev_setup/teardown()
 -----------------------------------------------------------

 Most drivers can use drm_fb_helper_fbdev_setup() except maybe:

 - amdgpu which has special logic to decide whether to call
   drm_helper_disable_unused_functions()

 - armada which isn't atomic and doesn't call
   drm_helper_disable_unused_functions()

 - i915 which calls drm_fb_helper_initial_config() in a worker

 Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can
 probably use drm_fb_helper_fbdev_teardown().

 Contact: Maintainer of the driver you plan to convert

 Clean up mmap forwarding
 ------------------------

 A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
 And also a lot of them forward dma-buf mmap to the gem mmap implementations.
 There's drm_gem_prime_mmap() for this now, but still needs to be rolled out.

 Contact: Daniel Vetter

 Generic fbdev defio support
 ---------------------------

 The defio support code in the fbdev core has some very specific requirements,
 which means drivers need to have a special framebuffer for fbdev. Which prevents
 us from using the generic fbdev emulation code everywhere. The main issue is
 that it uses some fields in struct page itself, which breaks shmem gem objects
 (and other things).

 Possible solution would be to write our own defio mmap code in the drm fbdev
 emulation. It would need to fully wrap the existing mmap ops, forwarding
 everything after it has done the write-protect/mkwrite trickery:

 - In the drm_fbdev_fb_mmap helper, if we need defio, change the
   default page prots to write-protected with something like this::

       vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot);

 - Set the mkwrite and fsync callbacks with similar implementions to the core
   fbdev defio stuff. These should all work on plain ptes, they don't actually
   require a struct page.  uff. These should all work on plain ptes, they don't
   actually require a struct page.

 - Track the dirty pages in a separate structure (bitfield with one bit per page
   should work) to avoid clobbering struct page.

 Might be good to also have some igt testcases for this.

 Contact: Daniel Vetter, Noralf Tronnes

 idr_init_base()
 ---------------

 DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
 userspace IDs to internal objects, and in most places ID=0 means NULL and hence
 is never used. Switching to idr_init_base() for these would make the idr more
 efficient.

 Contact: Daniel Vetter

 struct drm_gem_object_funcs
 ---------------------------

 GEM objects can now have a function table instead of having the callbacks on the
 DRM driver struct. This is now the preferred way and drivers can be moved over.

 We also need a 2nd version of the CMA define that doesn't require the
 vmapping to be present (different hook for prime importing). Plus this needs to
 be rolled out to all drivers using their own implementations, too.

 Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate
 ---------------------------------------------------------

 For cases where drivers are attempting to grab the modeset locks with a local
 acquire context. Replace the boilerplate code surrounding
 drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and
 DRM_MODESET_LOCK_ALL_END() instead.

 This should also be done for all places where drm_modest_lock_all() is still
 used.

 As a reference, take a look at the conversions already completed in drm core.

 Contact: Sean Paul, respective driver maintainers

 Rename CMA helpers to DMA helpers
 ---------------------------------

 CMA (standing for contiguous memory allocator) is really a bit an accident of
 what these were used for first, a much better name would be DMA helpers. In the
 text these should even be called coherent DMA memory helpers (so maybe CDM, but
 no one knows what that means) since underneath they just use dma_alloc_coherent.

 Contact: Laurent Pinchart, Daniel Vetter

 Convert direct mode.vrefresh accesses to use drm_mode_vrefresh()
 ----------------------------------------------------------------

 drm_display_mode.vrefresh isn't guaranteed to be populated. As such, using it
 is risky and has been known to cause div-by-zero bugs. Fortunately, drm core
 has helper which will use mode.vrefresh if it's !0 and will calculate it from
 the timings when it's 0.

 Use simple search/replace, or (more fun) cocci to replace instances of direct
 vrefresh access with a call to the helper. Check out
 https://lists.freedesktop.org/archives/dri-devel/2019-January/205186.html for
 inspiration.

 Once all instances of vrefresh have been converted, remove vrefresh from
 drm_display_mode to avoid future use.

 Contact: Sean Paul

 Remove drm_display_mode.hsync
 -----------------------------

 We have drm_mode_hsync() to calculate this from hsync_start/end, since drivers
 shouldn't/don't use this, remove this member to avoid any temptations to use it
 in the future. If there is any debug code using drm_display_mode.hsync, convert
 it to use drm_mode_hsync() instead.

 Contact: Sean Paul

 drm_fb_helper tasks
 -------------------

 - drm_fb_helper_restore_fbdev_mode_unlocked() should call restore_fbdev_mode()
   not the _force variant so it can bail out if there is a master. But first
   these igt tests need to be fixed: kms_fbcon_fbt@psr and
   kms_fbcon_fbt@psr-suspend.

 - The max connector argument for drm_fb_helper_init() and
   drm_fb_helper_fbdev_setup() isn't used anymore and can be removed.

 - The helper doesn't keep an array of connectors anymore so these can be
   removed: drm_fb_helper_single_add_all_connectors(),
   drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector().

 Core refactorings
 =================

 Clean up the DRM header mess
 ----------------------------

 The DRM subsystem originally had only one huge global header, ``drmP.h``. This
 is now split up, but many source files still include it. The remaining part of
 the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the
 headers needed (and fixing up any missing pre-declarations in the headers).

 In the end no .c file should need to include ``drmP.h`` anymore.

 Contact: Daniel Vetter

 Make panic handling work
 ------------------------

 This is a really varied tasks with lots of little bits and pieces:

 * The panic path can't be tested currently, leading to constant breaking. The
   main issue here is that panics can be triggered from hardirq contexts and
   hence all panic related callback can run in hardirq context. It would be
   awesome if we could test at least the fbdev helper code and driver code by
   e.g. trigger calls through drm debugfs files. hardirq context could be
   achieved by using an IPI to the local processor.

 * There's a massive confusion of different panic handlers. DRM fbdev emulation
   helpers have one, but on top of that the fbcon code itself also has one. We
   need to make sure that they stop fighting over each another.

 * ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
   isn't a full solution for panic paths. We need to make sure that it only
   returns true if there's a panic going on for real, and fix up all the
   fallout.

 * The panic handler must never sleep, which also means it can't ever
   ``mutex_lock()``. Also it can't grab any other lock unconditionally, not
   even spinlocks (because NMI and hardirq can panic too). We need to either
   make sure to not call such paths, or trylock everything. Really tricky.

 * For the above locking troubles reasons it's pretty much impossible to
   attempt a synchronous modeset from panic handlers. The only thing we could
   try to achive is an atomic ``set_base`` of the primary plane, and hope that
   it shows up. Everything else probably needs to be delayed to some worker or
   something else which happens later on. Otherwise it just kills the box
   harder, prevent the panic from going out on e.g. netconsole.

 * There's also proposal for a simplied DRM console instead of the full-blown
   fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
   obviously work for both console, in case we ever get kmslog merged.

 Contact: Daniel Vetter

 Clean up the debugfs support
 ----------------------------

 There's a bunch of issues with it:

 - The drm_info_list ->show() function doesn't even bother to cast to the drm
   structure for you. This is lazy.

 - We probably want to have some support for debugfs files on crtc/connectors and
   maybe other kms objects directly in core. There's even drm_print support in
   the funcs for these objects to dump kms state, so it's all there. And then the
   ->show() functions should obviously give you a pointer to the right object.

 - The drm_info_list stuff is centered on drm_minor instead of drm_device. For
   anything we want to print drm_device (or maybe drm_file) is the right thing.

 - The drm_driver->debugfs_init hooks we have is just an artifact of the old
   midlayered load sequence. DRM debugfs should work more like sysfs, where you
   can create properties/files for an object anytime you want, and the core
   takes care of publishing/unpuplishing all the files at register/unregister
   time. Drivers shouldn't need to worry about these technicalities, and fixing
   this (together with the drm_minor->drm_device move) would allow us to remove
   debugfs_init.

 - Drop the return code and error checking from all debugfs functions. Greg KH is
   working on this already.

 Contact: Daniel Vetter

 KMS cleanups
 ------------

 Some of these date from the very introduction of KMS in 2008 ...

 - Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
   function tables in drivers, but before we can remove them we need to make sure
   that all the users in helpers and drivers do correctly check for a NULL
   vtable.

 - Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
   drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
   end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
   historical reasons) misnamed drm_primary_helper_destroy() function.

 Level: Intermediate

 Remove automatic page mapping from dma-buf importing
 ----------------------------------------------------

 When importing dma-bufs, the dma-buf and PRIME frameworks automatically map
 imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and
 drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach()
 even if they never do actual device DMA, but only CPU access through
 dma_buf_vmap(). This is a problem for USB devices, which do not support DMA
 operations.

 To fix the issue, automatic page mappings should be removed from the
 buffer-sharing code. Fixing this is a bit more involved, since the import/export
 cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over
 this problem for USB devices by fishing out the USB host controller device, as
 long as that supports DMA. Otherwise importing can still needlessly fail.

 Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter

 Level: Advanced


 Better Testing
 ==============

 Enable trinity for DRM
 ----------------------

 And fix up the fallout. Should be really interesting ...

 Make KMS tests in i-g-t generic
 -------------------------------

 The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
 including tons of testcases for corner-cases in the modesetting API. It would
 be awesome if those tests (at least the ones not relying on Intel-specific GEM
 features) could be made to run on any KMS driver.

 Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
 converting things over. For modeset tests we also first need a bit of
 infrastructure to use dumb buffers for untiled buffers, to be able to run all
 the non-i915 specific modeset tests.

 Extend virtual test driver (VKMS)
 ---------------------------------

 See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
 internship task, since it only requires a virtual machine and can be sized to
 fit the available time.

 Contact: Daniel Vetter

 Backlight Refactoring
 ---------------------

 Backlight drivers have a triple enable/disable state, which is a bit overkill.
 Plan to fix this:

 1. Roll out backlight_enable() and backlight_disable() helpers everywhere. This
    has started already.
 2. In all, only look at one of the three status bits set by the above helpers.
 3. Remove the other two status bits.

 Contact: Daniel Vetter

 Driver Specific
 ===============

 AMD DC Display Driver
 ---------------------

 AMD DC is the display driver for AMD devices starting with Vega. There has been
 a bunch of progress cleaning it up but there's still plenty of work to be done.

 See drivers/gpu/drm/amd/display/TODO for tasks.

 Contact: Harry Wentland, Alex Deucher

 i915
 ----

 - Our early/late pm callbacks could be removed in favour of using
   device_link_add to model the dependency between i915 and snd_had. See
   https://dri.freedesktop.org/docs/drm/driver-api/device_link.html

 Bootsplash
 ==========

 There is support in place now for writing internal DRM clients making it
 possible to pick up the bootsplash work that was rejected because it was written
 for fbdev.

 - [v6,8/8] drm/client: Hack: Add bootsplash example
   https://patchwork.freedesktop.org/patch/306579/

 - [RFC PATCH v2 00/13] Kernel based bootsplash
   https://lkml.org/lkml/2017/12/13/764

 Contact: Sam Ravnborg

 Outside DRM
 ===========
	.. _todo:

	=========
	TODO list
	=========

	This section contains a list of smaller janitorial tasks in the kernel DRM
	graphics subsystem useful as newbie projects. Or for slow rainy days.

	Subsystem-wide refactorings
	===========================

	Remove custom dumb_map_offset implementations
	---------------------------------------------

	All GEM based drivers should be using drm_gem_create_mmap_offset() instead.
	Audit each individual driver, make sure it'll work with the generic
	implementation (there's lots of outdated locking leftovers in various
	implementations), and then remove it.

	Contact: Daniel Vetter, respective driver maintainers

	Convert existing KMS drivers to atomic modesetting
	--------------------------------------------------

	3.19 has the atomic modeset interfaces and helpers, so drivers can now be
	converted over. Modern compositors like Wayland or Surfaceflinger on Android
	really want an atomic modeset interface, so this is all about the bright
	future.

	There is a conversion guide for atomic and all you need is a GPU for a
	non-converted driver (again virtual HW drivers for KVM are still all
	suitable).

	As part of this drivers also need to convert to universal plane (which means
	exposing primary & cursor as proper plane objects). But that's much easier to
	do by directly using the new atomic helper driver callbacks.

	Contact: Daniel Vetter, respective driver maintainers

	Clean up the clipped coordination confusion around planes
	---------------------------------------------------------

	We have a helper to get this right with drm_plane_helper_check_update(), but
	it's not consistently used. This should be fixed, preferrably in the atomic
	helpers (and drivers then moved over to clipped coordinates). Probably the
	helper should also be moved from drm_plane_helper.c to the atomic helpers, to
	avoid confusion - the other helpers in that file are all deprecated legacy
	helpers.

	Contact: Ville Syrjälä, Daniel Vetter, driver maintainers

	Convert early atomic drivers to async commit helpers
	----------------------------------------------------

	For the first year the atomic modeset helpers didn't support asynchronous /
	nonblocking commits, and every driver had to hand-roll them. This is fixed
	now, but there's still a pile of existing drivers that easily could be
	converted over to the new infrastructure.

	One issue with the helpers is that they require that drivers handle completion
	events for atomic commits correctly. But fixing these bugs is good anyway.

	Contact: Daniel Vetter, respective driver maintainers

	Fallout from atomic KMS
	-----------------------

	``drm_atomic_helper.c`` provides a batch of functions which implement legacy
	IOCTLs on top of the new atomic driver interface. Which is really nice for
	gradual conversion of drivers, but unfortunately the semantic mismatches are
	a bit too severe. So there's some follow-up work to adjust the function
	interfaces to fix these issues:

	* atomic needs the lock acquire context. At the moment that's passed around
	implicitly with some horrible hacks, and it's also allocate with
	``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating
	the acquire context explicitly on stack and then also pass it down into
	drivers explicitly so that the legacy-on-atomic functions can use them.

	Except for some driver code this is done. This task should be finished by
	adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().

	* A bunch of the vtable hooks are now in the wrong place: DRM has a split
	between core vfunc tables (named ``drm_foo_funcs``), which are used to
	implement the userspace ABI. And then there's the optional hooks for the
	helper libraries (name ``drm_foo_helper_funcs``), which are purely for
	internal use. Some of these hooks should be move from ``_funcs`` to
	``_helper_funcs`` since they are not part of the core ABI. There's a
	``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``.

	Contact: Daniel Vetter

	Get rid of dev->struct_mutex from GEM drivers
	---------------------------------------------

	``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested
	everything. Nowadays in modern drivers the only bit where it's mandatory is
	serializing GEM buffer object destruction. Which unfortunately means drivers
	have to keep track of that lock and either call ``unreference`` or
	``unreference_locked`` depending upon context.

	Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8,
	and there's a ``gem_free_object_unlocked`` callback for any drivers which are
	entirely ``struct_mutex`` free.

	For drivers that need ``struct_mutex`` it should be replaced with a driver-
	private lock. The tricky part is the BO free functions, since those can't
	reliably take that lock any more. Instead state needs to be protected with
	suitable subordinate locks or some cleanup work pushed to a worker thread. For
	performance-critical drivers it might also be better to go with a more
	fine-grained per-buffer object and per-context lockings scheme. Currently only the
	``msm`` driver still use ``struct_mutex``.

	Contact: Daniel Vetter, respective driver maintainers

	Convert instances of dev_info/dev_err/dev_warn to their DRM_DEV_* equivalent
	----------------------------------------------------------------------------

	For drivers which could have multiple instances, it is necessary to
	differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR
	don't do this, drivers used dev_info/warn/err to make this differentiation. We
	now have DRM_DEV_* variants of the drm print macros, so we can start to convert
	those drivers back to using drm-formwatted specific log messages.

	Before you start this conversion please contact the relevant maintainers to make
	sure your work will be merged - not everyone agrees that the DRM dmesg macros
	are better.

	Contact: Sean Paul, Maintainer of the driver you plan to convert

	Convert drivers to use simple modeset suspend/resume
	----------------------------------------------------

	Most drivers (except i915 and nouveau) that use
	drm_atomic_helper_suspend/resume() can probably be converted to use
	drm_mode_config_helper_suspend/resume(). Also there's still open-coded version
	of the atomic suspend/resume code in older atomic modeset drivers.

	Contact: Maintainer of the driver you plan to convert

	Convert drivers to use drm_fb_helper_fbdev_setup/teardown()
	-----------------------------------------------------------

	Most drivers can use drm_fb_helper_fbdev_setup() except maybe:

	- amdgpu which has special logic to decide whether to call
	drm_helper_disable_unused_functions()

	- armada which isn't atomic and doesn't call
	drm_helper_disable_unused_functions()

	- i915 which calls drm_fb_helper_initial_config() in a worker

	Drivers that use drm_framebuffer_remove() to clean up the fbdev framebuffer can
	probably use drm_fb_helper_fbdev_teardown().

	Contact: Maintainer of the driver you plan to convert

	Clean up mmap forwarding
	------------------------

	A lot of drivers forward gem mmap calls to dma-buf mmap for imported buffers.
	And also a lot of them forward dma-buf mmap to the gem mmap implementations.
	There's drm_gem_prime_mmap() for this now, but still needs to be rolled out.

	Contact: Daniel Vetter

	Generic fbdev defio support
	---------------------------

	The defio support code in the fbdev core has some very specific requirements,
	which means drivers need to have a special framebuffer for fbdev. Which prevents
	us from using the generic fbdev emulation code everywhere. The main issue is
	that it uses some fields in struct page itself, which breaks shmem gem objects
	(and other things).

	Possible solution would be to write our own defio mmap code in the drm fbdev
	emulation. It would need to fully wrap the existing mmap ops, forwarding
	everything after it has done the write-protect/mkwrite trickery:

	- In the drm_fbdev_fb_mmap helper, if we need defio, change the
	default page prots to write-protected with something like this::

	vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot);

	- Set the mkwrite and fsync callbacks with similar implementions to the core
	fbdev defio stuff. These should all work on plain ptes, they don't actually
	require a struct page. uff. These should all work on plain ptes, they don't
	actually require a struct page.

	- Track the dirty pages in a separate structure (bitfield with one bit per page
	should work) to avoid clobbering struct page.

	Might be good to also have some igt testcases for this.

	Contact: Daniel Vetter, Noralf Tronnes

	idr_init_base()
	---------------

	DRM core&drivers uses a lot of idr (integer lookup directories) for mapping
	userspace IDs to internal objects, and in most places ID=0 means NULL and hence
	is never used. Switching to idr_init_base() for these would make the idr more
	efficient.

	Contact: Daniel Vetter

	struct drm_gem_object_funcs
	---------------------------

	GEM objects can now have a function table instead of having the callbacks on the
	DRM driver struct. This is now the preferred way and drivers can be moved over.

	We also need a 2nd version of the CMA define that doesn't require the
	vmapping to be present (different hook for prime importing). Plus this needs to
	be rolled out to all drivers using their own implementations, too.

	Use DRM_MODESET_LOCK_ALL_* helpers instead of boilerplate
	---------------------------------------------------------

	For cases where drivers are attempting to grab the modeset locks with a local
	acquire context. Replace the boilerplate code surrounding
	drm_modeset_lock_all_ctx() with DRM_MODESET_LOCK_ALL_BEGIN() and
	DRM_MODESET_LOCK_ALL_END() instead.

	This should also be done for all places where drm_modest_lock_all() is still
	used.

	As a reference, take a look at the conversions already completed in drm core.

	Contact: Sean Paul, respective driver maintainers

	Rename CMA helpers to DMA helpers
	---------------------------------

	CMA (standing for contiguous memory allocator) is really a bit an accident of
	what these were used for first, a much better name would be DMA helpers. In the
	text these should even be called coherent DMA memory helpers (so maybe CDM, but
	no one knows what that means) since underneath they just use dma_alloc_coherent.

	Contact: Laurent Pinchart, Daniel Vetter

	Convert direct mode.vrefresh accesses to use drm_mode_vrefresh()
	----------------------------------------------------------------

	drm_display_mode.vrefresh isn't guaranteed to be populated. As such, using it
	is risky and has been known to cause div-by-zero bugs. Fortunately, drm core
	has helper which will use mode.vrefresh if it's !0 and will calculate it from
	the timings when it's 0.

	Use simple search/replace, or (more fun) cocci to replace instances of direct
	vrefresh access with a call to the helper. Check out
	https://lists.freedesktop.org/archives/dri-devel/2019-January/205186.html for
	inspiration.

	Once all instances of vrefresh have been converted, remove vrefresh from
	drm_display_mode to avoid future use.

	Contact: Sean Paul

	Remove drm_display_mode.hsync
	-----------------------------

	We have drm_mode_hsync() to calculate this from hsync_start/end, since drivers
	shouldn't/don't use this, remove this member to avoid any temptations to use it
	in the future. If there is any debug code using drm_display_mode.hsync, convert
	it to use drm_mode_hsync() instead.

	Contact: Sean Paul

	drm_fb_helper tasks
	-------------------

	- drm_fb_helper_restore_fbdev_mode_unlocked() should call restore_fbdev_mode()
	not the _force variant so it can bail out if there is a master. But first
	these igt tests need to be fixed: kms_fbcon_fbt@psr and
	kms_fbcon_fbt@psr-suspend.

	- The max connector argument for drm_fb_helper_init() and
	drm_fb_helper_fbdev_setup() isn't used anymore and can be removed.

	- The helper doesn't keep an array of connectors anymore so these can be
	removed: drm_fb_helper_single_add_all_connectors(),
	drm_fb_helper_add_one_connector() and drm_fb_helper_remove_one_connector().

	Core refactorings
	=================

	Clean up the DRM header mess
	----------------------------

	The DRM subsystem originally had only one huge global header, ``drmP.h``. This
	is now split up, but many source files still include it. The remaining part of
	the cleanup work here is to replace any ``#include <drm/drmP.h>`` by only the
	headers needed (and fixing up any missing pre-declarations in the headers).

	In the end no .c file should need to include ``drmP.h`` anymore.

	Contact: Daniel Vetter

	Make panic handling work
	------------------------

	This is a really varied tasks with lots of little bits and pieces:

	* The panic path can't be tested currently, leading to constant breaking. The
	main issue here is that panics can be triggered from hardirq contexts and
	hence all panic related callback can run in hardirq context. It would be
	awesome if we could test at least the fbdev helper code and driver code by
	e.g. trigger calls through drm debugfs files. hardirq context could be
	achieved by using an IPI to the local processor.

	* There's a massive confusion of different panic handlers. DRM fbdev emulation
	helpers have one, but on top of that the fbcon code itself also has one. We
	need to make sure that they stop fighting over each another.

	* ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and
	isn't a full solution for panic paths. We need to make sure that it only
	returns true if there's a panic going on for real, and fix up all the
	fallout.

	* The panic handler must never sleep, which also means it can't ever
	``mutex_lock()``. Also it can't grab any other lock unconditionally, not
	even spinlocks (because NMI and hardirq can panic too). We need to either
	make sure to not call such paths, or trylock everything. Really tricky.

	* For the above locking troubles reasons it's pretty much impossible to
	attempt a synchronous modeset from panic handlers. The only thing we could
	try to achive is an atomic ``set_base`` of the primary plane, and hope that
	it shows up. Everything else probably needs to be delayed to some worker or
	something else which happens later on. Otherwise it just kills the box
	harder, prevent the panic from going out on e.g. netconsole.

	* There's also proposal for a simplied DRM console instead of the full-blown
	fbcon and DRM fbdev emulation. Any kind of panic handling tricks should
	obviously work for both console, in case we ever get kmslog merged.

	Contact: Daniel Vetter

	Clean up the debugfs support
	----------------------------

	There's a bunch of issues with it:

	- The drm_info_list ->show() function doesn't even bother to cast to the drm
	structure for you. This is lazy.

	- We probably want to have some support for debugfs files on crtc/connectors and
	maybe other kms objects directly in core. There's even drm_print support in
	the funcs for these objects to dump kms state, so it's all there. And then the
	->show() functions should obviously give you a pointer to the right object.

	- The drm_info_list stuff is centered on drm_minor instead of drm_device. For
	anything we want to print drm_device (or maybe drm_file) is the right thing.

	- The drm_driver->debugfs_init hooks we have is just an artifact of the old
	midlayered load sequence. DRM debugfs should work more like sysfs, where you
	can create properties/files for an object anytime you want, and the core
	takes care of publishing/unpuplishing all the files at register/unregister
	time. Drivers shouldn't need to worry about these technicalities, and fixing
	this (together with the drm_minor->drm_device move) would allow us to remove
	debugfs_init.

	- Drop the return code and error checking from all debugfs functions. Greg KH is
	working on this already.

	Contact: Daniel Vetter

	KMS cleanups
	------------

	Some of these date from the very introduction of KMS in 2008 ...

	- Make ->funcs and ->helper_private vtables optional. There's a bunch of empty
	function tables in drivers, but before we can remove them we need to make sure
	that all the users in helpers and drivers do correctly check for a NULL
	vtable.

	- Cleanup up the various ->destroy callbacks. A lot of them just wrapt the
	drm_*_cleanup implementations and can be removed. Some tack a kfree() at the
	end, for which we could add drm_*_cleanup_kfree(). And then there's the (for
	historical reasons) misnamed drm_primary_helper_destroy() function.

	Level: Intermediate

	Remove automatic page mapping from dma-buf importing
	----------------------------------------------------

	When importing dma-bufs, the dma-buf and PRIME frameworks automatically map
	imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and
	drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach()
	even if they never do actual device DMA, but only CPU access through
	dma_buf_vmap(). This is a problem for USB devices, which do not support DMA
	operations.

	To fix the issue, automatic page mappings should be removed from the
	buffer-sharing code. Fixing this is a bit more involved, since the import/export
	cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over
	this problem for USB devices by fishing out the USB host controller device, as
	long as that supports DMA. Otherwise importing can still needlessly fail.

	Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter

	Level: Advanced


	Better Testing
	==============

	Enable trinity for DRM
	----------------------

	And fix up the fallout. Should be really interesting ...

	Make KMS tests in i-g-t generic
	-------------------------------

	The i915 driver team maintains an extensive testsuite for the i915 DRM driver,
	including tons of testcases for corner-cases in the modesetting API. It would
	be awesome if those tests (at least the ones not relying on Intel-specific GEM
	features) could be made to run on any KMS driver.

	Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass-
	converting things over. For modeset tests we also first need a bit of
	infrastructure to use dumb buffers for untiled buffers, to be able to run all
	the non-i915 specific modeset tests.

	Extend virtual test driver (VKMS)
	---------------------------------

	See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal
	internship task, since it only requires a virtual machine and can be sized to
	fit the available time.

	Contact: Daniel Vetter

	Backlight Refactoring
	---------------------

	Backlight drivers have a triple enable/disable state, which is a bit overkill.
	Plan to fix this:

	1. Roll out backlight_enable() and backlight_disable() helpers everywhere. This
	has started already.
	2. In all, only look at one of the three status bits set by the above helpers.
	3. Remove the other two status bits.

	Contact: Daniel Vetter

	Driver Specific
	===============

	AMD DC Display Driver
	---------------------

	AMD DC is the display driver for AMD devices starting with Vega. There has been
	a bunch of progress cleaning it up but there's still plenty of work to be done.

	See drivers/gpu/drm/amd/display/TODO for tasks.

	Contact: Harry Wentland, Alex Deucher

	i915
	----

	- Our early/late pm callbacks could be removed in favour of using
	device_link_add to model the dependency between i915 and snd_had. See
	https://dri.freedesktop.org/docs/drm/driver-api/device_link.html

	Bootsplash
	==========

	There is support in place now for writing internal DRM clients making it
	possible to pick up the bootsplash work that was rejected because it was written
	for fbdev.

	- [v6,8/8] drm/client: Hack: Add bootsplash example
	https://patchwork.freedesktop.org/patch/306579/

	- [RFC PATCH v2 00/13] Kernel based bootsplash
	https://lkml.org/lkml/2017/12/13/764

	Contact: Sam Ravnborg

	Outside DRM
	===========