[PATCH 0/2] drm/amdgpu/display: Make multi-plane configurations more flexible

[<sunpeng.li@amd.com>]

From: Leo Li <sunpeng.li@amd.com>

These patches aim to make the amdgpgu KMS driver play nicer with compositors
when building multi-plane scanout configurations. They do so by:

1. Making cursor behavior more sensible.
2. Allowing placement of DRM OVERLAY planes underneath the PRIMARY plane for
   'underlay' configurations (perhaps more of a RFC, see below).

Please see the commit messages for details.


For #2, the simplest way to accomplish this was to increase the value of the
immutable zpos property for the PRIMARY plane. This allowed OVERLAY planes with
a mutable zpos range of (0-254) to be positioned underneath the PRIMARY for an
underlay scanout configuration.

Technically speaking, DCN hardware does not have a concept of primary or overlay
planes - there are simply 4 general purpose hardware pipes that can be maped in
any configuration. So the immutable zpos restriction on the PRIMARY plane is
kind of arbitrary; it can have a mutable range of (0-254) just like the
OVERLAYs. The distinction between PRIMARY and OVERLAY planes is also somewhat
arbitrary. We can interpret PRIMARY as the first plane that should be enabled on
a CRTC, but beyond that, it doesn't mean much for amdgpu.

Therefore, I'm curious about how compositors devs understand KMS planes and
their zpos properties, and how we would like to use them. It isn't clear to me
how compositors wish to interpret and use the DRM zpos property, or
differentiate between OVERLAY and PRIMARY planes, when it comes to setting up
multi-plane scanout.

Ultimately, what I'd like to answer is "What can we do on the KMS driver and DRM
plane API side, that can make building multi-plane scanout configurations easier
for compositors?" I'm hoping we can converge on something, whether that be
updating the existing documentation to better define the usage, or update the
API to provide support for something that is lacking.

Thanks,
Leo


Some links to provide context and details:
* What is underlay?: https://gitlab.freedesktop.org/emersion/libliftoff/-/issues/76
* Discussion on how to implement underlay on Weston: https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/1258#note_2325164

Cc: Joshua Ashton <joshua@froggi.es>
Cc: Michel Dänzer <mdaenzer@redhat.com>
Cc: Chao Guo <chao.guo@nxp.com>
Cc: Xaver Hugl <xaver.hugl@gmail.com>
Cc: Vikas Korjani <Vikas.Korjani@amd.com>
Cc: Robert Mader <robert.mader@posteo.de>
Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Simon Ser <contact@emersion.fr>
Cc: Shashank Sharma <shashank.sharma@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Sebastian Wick <sebastian.wick@redhat.com>

Leo Li (2):
  drm/amd/display: Introduce overlay cursor mode
  drm/amd/display: Move PRIMARY plane zpos higher

 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 405 ++++++++++++++++--
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h |   7 +
 .../amd/display/amdgpu_dm/amdgpu_dm_crtc.c    |   1 +
 .../amd/display/amdgpu_dm/amdgpu_dm_plane.c   |  28 +-
 4 files changed, 391 insertions(+), 50 deletions(-)

-- 
2.44.0