Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 479 insertions, 0 deletions

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+.. _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
+===========================
+
+De-midlayer drivers
+-------------------
+
+With the recent ``drm_bus`` cleanup patches for 3.17 it is no longer required
+to have a ``drm_bus`` structure set up. Drivers can directly set up the
+``drm_device`` structure instead of relying on bus methods in ``drm_usb.c``
+and ``drm_pci.c``. The goal is to get rid of the driver's ``->load`` /
+``->unload`` callbacks and open-code the load/unload sequence properly, using
+the new two-stage ``drm_device`` setup/teardown.
+
+Once all existing drivers are converted we can also remove those bus support
+files for USB and platform devices.
+
+All you need is a GPU for a non-converted driver (currently almost all of
+them, but also all the virtual ones used by KVM, so everyone qualifies).
+
+Contact: Daniel Vetter, Thierry Reding, respective driver maintainers
+
+Switch from reference/unreference to get/put
+--------------------------------------------
+
+For some reason DRM core uses ``reference``/``unreference`` suffixes for
+refcounting functions, but kernel uses ``get``/``put`` (e.g.
+``kref_get``/``put()``). It would be good to switch over for consistency, and
+it's shorter. Needs to be done in 3 steps for each pair of functions:
+
+* Create new ``get``/``put`` functions, define the old names as compatibility
+  wrappers
+* Switch over each file/driver using a cocci-generated spatch.
+* Once all users of the old names are gone, remove them.
+
+This way drivers/patches in the progress of getting merged won't break.
+
+Contact: Daniel Vetter
+
+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
+
+Better manual-upload support for atomic
+---------------------------------------
+
+This would be especially useful for tinydrm:
+
+- Add a struct drm_rect dirty_clip to drm_crtc_state. When duplicating the
+  crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in
+  __drm_atomic_helper_crtc_duplicate_state().
+
+- Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_
+  prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this
+  is a function useful to implement the fb->dirty function.
+
+- Create a new drm_fb_dirty function which does essentially what e.g.
+  mipi_dbi_fb_dirty does. You can use e.g. drm_atomic_helper_update_plane as the
+  template. But instead of doing a simple full-screen plane update, this new
+  helper also sets crtc_state->dirty_clip to the right coordinates. And of
+  course it needs to check whether the fb is actually active (and maybe where),
+  so there's some book-keeping involved. There's also some good fun involved in
+  scaling things appropriately. For that case we might simply give up and
+  declare the entire area covered by the plane as dirty.
+
+Contact: Noralf Trønnes, Daniel Vetter
+
+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.
+
+* 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``.
+
+* There's a new helper ``drm_atomic_helper_best_encoder()`` which could be
+  used by all atomic drivers which don't select the encoder for a given
+  connector at runtime. That's almost all of them, and would allow us to get
+  rid of a lot of ``best_encoder`` boilerplate in drivers.
+
+  This was almost done, but new drivers added a few more cases again.
+
+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 the
+following drivers still use ``struct_mutex``: ``msm``, ``omapdrm`` and
+``udl``.
+
+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().
+
+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.
+Would be great to refactor this all into a set of small common helpers.
+
+Contact: Daniel Vetter
+
+Put a reservation_object into drm_gem_object
+--------------------------------------------
+
+This would remove the need for the ->gem_prime_res_obj callback. It would also
+allow us to implement generic helpers for waiting for a bo, allowing for quite a
+bit of refactoring in the various wait ioctl implementations.
+
+Contact: Daniel Vetter
+
+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
+
+Core refactorings
+=================
+
+Clean up the DRM header mess
+----------------------------
+
+Currently the DRM subsystem has only one global header, ``drmP.h``. This is
+used both for functions exported to helper libraries and drivers and functions
+only used internally in the ``drm.ko`` module. The goal would be to move all
+header declarations not needed outside of ``drm.ko`` into
+``drivers/gpu/drm/drm_*_internal.h`` header files. ``EXPORT_SYMBOL`` also
+needs to be dropped for these functions.
+
+This would nicely tie in with the below task to create kerneldoc after the API
+is cleaned up. Or with the "hide legacy cruft better" task.
+
+Note that this is well in progress, but ``drmP.h`` is still huge. The updated
+plan is to switch to per-file driver API headers, which will also structure
+the kerneldoc better. This should also allow more fine-grained ``#include``
+directives.
+
+In the end no .c file should need to include ``drmP.h`` anymore.
+
+Contact: Daniel Vetter
+
+Add missing kerneldoc for exported functions
+--------------------------------------------
+
+The DRM reference documentation is still lacking kerneldoc in a few areas. The
+task would be to clean up interfaces like moving functions around between
+files to better group them and improving the interfaces like dropping return
+values for functions that never fail. Then write kerneldoc for all exported
+functions and an overview section and integrate it all into the drm book.
+
+See https://dri.freedesktop.org/docs/drm/ for what's there already.
+
+Contact: Daniel Vetter
+
+Hide legacy cruft better
+------------------------
+
+Way back DRM supported only drivers which shadow-attached to PCI devices with
+userspace or fbdev drivers setting up outputs. Modern DRM drivers take charge
+of the entire device, you can spot them with the DRIVER_MODESET flag.
+
+Unfortunately there's still large piles of legacy code around which needs to
+be hidden so that driver writers don't accidentally end up using it. And to
+prevent security issues in those legacy IOCTLs from being exploited on modern
+drivers. This has multiple possible subtasks:
+
+* Extract support code for legacy features into a ``drm-legacy.ko`` kernel
+  module and compile it only when one of the legacy drivers is enabled.
+
+This is mostly done, the only thing left is to split up ``drm_irq.c`` into
+legacy cruft and the parts needed by modern KMS drivers.
+
+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.
+
+Contact: Daniel Vetter
+
+KMS cleanups
+------------
+
+Some of these date from the very introduction of KMS in 2008 ...
+
+- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should
+  be renamed to drm_mode_config.object_idr.
+
+- drm_display_mode doesn't need to be derived from drm_mode_object. That's
+  leftovers from older (never merged into upstream) KMS designs where modes
+  where set using their ID, including support to add/remove modes.
+
+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.
+
+Contact: Daniel Vetter
+
+Create a virtual KMS driver for testing (vkms)
+----------------------------------------------
+
+With all the latest helpers it should be fairly simple to create a virtual KMS
+driver useful for testing, or for running X or similar on headless machines
+(to be able to still use the GPU). This would be similar to vgem, but aimed at
+the modeset side.
+
+Once the basics are there there's tons of possibilities to extend it.
+
+Contact: Daniel Vetter
+
+Driver Specific
+===============
+
+tinydrm
+-------
+
+Tinydrm is the helper driver for really simple fb drivers. The goal is to make
+those drivers as simple as possible, so lots of room for refactoring:
+
+- backlight helpers, probably best to put them into a new drm_backlight.c.
+  This is because drivers/video is de-facto unmaintained. We could also
+  move drivers/video/backlight to drivers/gpu/backlight and take it all
+  over within drm-misc, but that's more work. Backlight helpers require a fair
+  bit of reworking and refactoring. A simple example is the enabling of a backlight.
+  Tinydrm has helpers for this. It would be good if other drivers can also use the
+  helper. However, there are various cases we need to consider i.e different
+  drivers seem to have different ways of enabling/disabling a backlight.
+  We also need to consider the backlight drivers (like gpio_backlight). The situation
+  is further complicated by the fact that the backlight is tied to fbdev
+  via fb_notifier_callback() which has complicated logic. For further details, refer
+  to the following discussion thread:
+  https://groups.google.com/forum/#!topic/outreachy-kernel/8rBe30lwtdA
+
+- spi helpers, probably best put into spi core/helper code. Thierry said
+  the spi maintainer is fast&reactive, so shouldn't be a big issue.
+
+- extract the mipi-dbi helper (well, the non-tinydrm specific parts at
+  least) into a separate helper, like we have for mipi-dsi already. Or follow
+  one of the ideas for having a shared dsi/dbi helper, abstracting away the
+  transport details more.
+
+- tinydrm_gem_cma_prime_import_sg_table should probably go into the cma
+  helpers, as a _vmapped variant (since not every driver needs the vmap).
+  And tinydrm_gem_cma_free_object could the be merged into
+  drm_gem_cma_free_object().
+
+- tinydrm_fb_create we could move into drm_simple_pipe, only need to add
+  the fb_create hook to drm_simple_pipe_funcs, which would again simplify a
+  bunch of things (since it gives you a one-stop vfunc for simple drivers).
+
+- Quick aside: The unregister devm stuff is kinda getting the lifetimes of
+  a drm_device wrong. Doesn't matter, since everyone else gets it wrong
+  too :-)
+
+- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above.
+
+Contact: Noralf Trønnes, Daniel Vetter
+
+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
+
+Outside DRM
+===========