You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
394 lines
17 KiB
394 lines
17 KiB
.. _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
|
|
|
|
Implement deferred fbdev setup in the helper
|
|
--------------------------------------------
|
|
|
|
Many (especially embedded drivers) want to delay fbdev setup until there's a
|
|
real screen plugged in. This is to avoid the dreaded fallback to the low-res
|
|
fbdev default. Many drivers have a hacked-up (and often broken) version of this,
|
|
better to do it once in the shared helpers. Thierry has a patch series, but that
|
|
one needs to be rebased and final polish applied.
|
|
|
|
Contact: Thierry Reding, 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.
|
|
|
|
* 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.
|
|
|
|
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
|
|
|
|
Core refactorings
|
|
=================
|
|
|
|
Use new IDR deletion interface to clean up drm_gem_handle_delete()
|
|
------------------------------------------------------------------
|
|
|
|
See the "This is gross" comment -- apparently the IDR system now can return an
|
|
error code instead of oopsing.
|
|
|
|
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
|
|
|
|
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.
|
|
|
|
- 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_lastclose could be drm_fb_helper_lastclose. Only thing we need
|
|
for that is to store the drm_fb_helper pointer somewhere in
|
|
drm_device->mode_config. And then we could roll that out to all the
|
|
drivers.
|
|
|
|
- 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 :-)
|
|
|
|
- With the fbdev pointer in dev->mode_config we could also make
|
|
suspend/resume helpers entirely generic, at least if we add a
|
|
dev->mode_config.suspend_state. We could even provide a generic pm_ops
|
|
structure with those.
|
|
|
|
- also rework the drm_framebuffer_funcs->dirty hook wire-up, see above.
|
|
|
|
Contact: Noralf Trønnes, Daniel Vetter
|
|
|
|
Outside DRM
|
|
===========
|
|
|