Re: [PATCH] drm/vkms: Extend todo

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Oct 03, 2018 at 10:35:18AM -0300, Rodrigo Siqueira wrote:
> On 10/03, Daniel Vetter wrote:
> > Typed up all the items Rodrigo capture at the vkms workshop at
> > xdc2018:
> > 
> > https://etherpad.net/p/vkms_todo
> > 
> > v2: Review from Rodrigo.
> > - Add eBPF for atomic check, I forgot it.
> > - Improve spelling.
> > 
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Gustavo Padovan <gustavo@padovan.org>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Sean Paul <sean@poorly.run>
> > Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
> > Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> > ---
> >  Documentation/gpu/vkms.rst | 101 ++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 99 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
> > index 0a6ea6216e41..7dfc349a4508 100644
> > --- a/Documentation/gpu/vkms.rst
> > +++ b/Documentation/gpu/vkms.rst
> > @@ -10,8 +10,8 @@
> >  TODO
> >  ====
> >  
> > -CRC API
> > --------
> > +CRC API Improvements
> > +--------------------
> >  
> >  - Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``
> >  
> > @@ -22,3 +22,100 @@ CRC API
> >  
> >  - Add igt test to check extreme alpha values i.e. fully opaque and fully
> >    transparent (intermediate values are affected by hw-specific rounding modes).
> > +
> > +Vblank issues
> > +-------------
> > +
> > +Some IGT test cases are failing. Need to analyze why and fix the issues:
> > +
> > +- plain-flip-fb-recreate
> > +- plain-flip-ts-check
> > +- flip-vs-blocking-wf-vblank
> > +- plain-flip-fb-recreate-interruptible
> > +- flip-vs-wf_vblank-interruptible
> > +
> > +Runtime Configuration
> > +---------------------
> > +
> > +We want to be able to reconfigure vkms instance without having to reload the
> > +module. Use/Test-cases:
> > +
> > +- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling of
> > +  compositors).
> > +
> > +- Configure planes/crtcs/connectors (we'd need some code to have more than 1 of
> > +  them first).
> > +
> > +- Change output configuration: Plug/unplug screens, change EDID, allow changing
> > +  the refresh rate.
> > +
> > +The currently proposed solution is to expose vkms configuration through
> > +configfs.  All existing module options should be supported through configfs too.
> > +
> > +Add Plane Features
> > +------------------
> > +
> > +There's lots of plane features we could add support for:
> > +
> > +- Real overlay planes, not just cursor.
> > +
> > +- Full alpha blending on all planes.
> > +
> > +- Rotation, scaling.
> > +
> > +- Additional buffer formats, especially YUV formats for video like NV12.
> > +  Low/high bpp RGB formats would also be interesting.
> > +
> > +- Async updates (currently only possible on cursor plane using the legacy cursor
> > +  api).
> > +
> > +For all of these, we also want to review the igt test coverage and make sure all
> > +relevant igt testcases work on vkms.
> > +
> > +Writeback support
> > +-----------------
> > +
> > +Currently vkms only computes a CRC for each frame. Once we have additional plane
> > +features, we could write back the entire composited frame, and expose it as:
> > +
> > +- Writeback connector. This is useful for testing compositors if you don't have
> > +  hardware with writeback support.
> > +
> > +- As a v4l device. This is useful for debugging compositors on special vkms
> > +  configurations, so that developers see what's really going on.
> > +
> > +Prime Buffer Sharing
> > +--------------------
> > +
> > +We already have vgem, which is a gem driver for testing rendering, similar to
> > +how vkms is for testing the modeset side. Adding buffer sharing support to vkms
> > +allows us to test them together, to test synchronization and lots of other
> > +features. Also, this allows compositors to test whether they work correctly on
> > +SoC chips, where the display and rendering is very often split between 2
> > +drivers.
> > +
> > +Output Features
> > +---------------
> > +
> > +- Variable refresh rate/freesync support. This probably needs prime buffer
> > +  sharing support, so that we can use vgem fences to simulate rendering in
> > +  testing. Also needs support to specify the EDID.
> > +
> > +- Add support for link status, so that compositors can validate their runtime
> > +  fallbacks when e.g. a Display Port link goes bad.
> > +
> > +- All the hotplug handling describe under "Runtime Configuration".
> > +
> > +Atomic Check using eBPF
> > +-----------------------
> > +
> > +Atomic drivers have lots of restrictions which are not exposed to userspace in
> > +any explicit form through e.g. possible property values. Userspace can only
> > +inquiry about these limits through the atomic IOCTL, possibly using the
> > +TEST_ONLY flag. Trying to add configurable code for all these limits, to allow
> > +compositors to be tested against them, would be rather futile exercise. Instead
> > +we could add support for eBPF to validate any kind of atomic state, and
> > +implement a library of different restrictions.
> > +
> > +This needs a bunch of features (plane compositing, multiple outputs, ...)
> > +enabled already to make sense.
> > -- 
> > 2.19.0.rc2
> > 
> 
> Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>

Thanks for your review, patch applied to drm-misc-next.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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