[RFC/PATCH v2 0/5] Add live source objects to DRM

[Laurent Pinchart]

Hello,

Here's a proposal for a different approach to live source in DRM based on an
idea by Daniel Vetter. The previous version can be found at
http://lists.freedesktop.org/archives/dri-devel/2015-March/079319.html.

The need comes from the Renesas R-Car SoCs in which a video processing engine
(named VSP1) that operates from memory to memory has one output directly
connected to a plane of the display engine (DU) without going through memory.

The VSP1 is supported by a V4L2 driver. While it could be argued that it
should instead be supported directly by the DRM rcar-du driver, this wouldn't
be a good idea for at least two reasons. First, the R-Car SoCs contain several
VSP1 instances, of which only a subset have a direct DU connection. The only
other instances operate solely in memory to memory mode. Then, the VSP1 is a
video processing engine and not a display engine. Its features are easily
supported by the V4L2 API, but don't map to the DRM/KMS API. Significant
changes to DRM/KMS would be required, beyond what is in my opinion an
acceptable scope for a display API.

Now that the need to interface two separate devices supported by two different
drivers in two separate subsystems has been established, we need an API to do
so. It should be noted that while that API doesn't exist in the mainline
kernel, the need isn't limited to Renesas SoCs.

This patch set proposes one possible solution for the problem in the form of a
new DRM object named live source. Live sources are created by drivers to model
hardware connections between a plane input and an external source, and are
attached to planes through the KMS userspace API.

Patch 1/5 adds live source objects to DRM, with an in-kernel API for drivers
to register the sources, and a userspace API to enumerate them.

Patch 2/5 implements connection between live sources and planes through
framebuffers. It introduces a new live source flag for framebuffers. When a
framebuffer is created with that flag set, a live source is associated with
the framebuffer instead of buffer objects. The framebuffer can then be used
with a plane to connect it with the live source. This is the biggest
difference compared to the previous approach, and has several benefits:

- Changes are less intrusive in the DRM core
- The implementation supports both the legacy API and atomic updates without
  any code specific to either
- No changes to existing drivers are needed
- The framebuffer format and size configuration API is reused

The framebuffer format and size should ideally be validated using information
queried directly from the driver that supports the live source device, but
I've decided not to implement such communication between V4L2 and DRM/KMS at
the moment to keep the proposal simple.

Patches 3/5 to 5/5 then implement support for live sources in the R-Car DU
driver. The rcar_du_live_framebuffer structure and its associated helper
functions could be moved to the DRM core later if other drivers need a similar
implementation. I've decided to keep them in the rcar-du driver for now as
it's not clear yet what other drivers might need.

Once again nothing here is set in stone.

Laurent Pinchart (5):
  drm: Add live source object
  drm: Connect live source to framebuffers
  drm/rcar-du: Add VSP1 support to the planes allocator
  drm/rcar-du: Add VSP1 live source support
  drm/rcar-du: Restart the DU group when a plane source changes

 drivers/gpu/drm/drm_crtc.c              | 287 +++++++++++++++++++++++++++++---
 drivers/gpu/drm/drm_ioctl.c             |   2 +
 drivers/gpu/drm/rcar-du/rcar_du_crtc.c  |  10 +-
 drivers/gpu/drm/rcar-du/rcar_du_drv.c   |   6 +-
 drivers/gpu/drm/rcar-du/rcar_du_drv.h   |   3 +
 drivers/gpu/drm/rcar-du/rcar_du_group.c |  21 ++-
 drivers/gpu/drm/rcar-du/rcar_du_group.h |   2 +
 drivers/gpu/drm/rcar-du/rcar_du_kms.c   | 132 ++++++++++++++-
 drivers/gpu/drm/rcar-du/rcar_du_kms.h   |   3 +
 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 191 ++++++++++++++++-----
 drivers/gpu/drm/rcar-du/rcar_du_plane.h |  11 ++
 drivers/gpu/drm/rcar-du/rcar_du_regs.h  |   1 +
 include/drm/drm_crtc.h                  |  35 ++++
 include/uapi/drm/drm.h                  |   3 +
 include/uapi/drm/drm_mode.h             |  23 +++
 15 files changed, 647 insertions(+), 83 deletions(-)

-- 
Regards,

Laurent Pinchart