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

[Laurent Pinchart]

Hello,

I have a feeling that RFC/PATCH will work better than just RFC, so here's a
patch set that adds a new object named live source to DRM.

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 and configure them.
Configuring a live source sets the width, height and pixel format of the
video stream. This should ideally be 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.

Patch 2/2 implements connection between live sources and planes. This takes
different forms depending on whether drivers use the setplane or the atomic
updates API:

- For setplane, the fb field can now contain a live source ID in addition to
  a framebuffer ID. As DRM allocates object IDs from a single ID space, the
  type can be inferred from the ID. This makes specifying both a framebuffer
  and a live source impossible, which isn't an issue given that such a
  configuration would be invalid.

  The live source is looked up by the DRM core and passed as a pointer to the
  .update_plane() operation. Unlike framebuffers live sources are not
  refcounted as they're created statically at driver initialization time.

- For atomic update, a new SRC_ID property has been added to planes. The live
  source is looked up from the source ID and stored into the plane state.

Patches 3/5 to 5/5 then implement support for live sources in the R-Car DU
driver.

Nothing here is set in stone. One point I'm not sure about is whether live
sources support should be enabled for setplane or only for atomic updates.
Other parts of the API can certainly be modified as well, and I'm open for
totally different implementations as well.

Laurent Pinchart (5):
  drm: Add live source object
  drm: Connect live source to plane
  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/armada/armada_overlay.c     |   2 +-
 drivers/gpu/drm/drm_atomic.c                |   7 +
 drivers/gpu/drm/drm_atomic_helper.c         |   4 +
 drivers/gpu/drm/drm_crtc.c                  | 365 ++++++++++++++++++++++++++--
 drivers/gpu/drm/drm_fops.c                  |   6 +-
 drivers/gpu/drm/drm_ioctl.c                 |   3 +
 drivers/gpu/drm/drm_plane_helper.c          |   1 +
 drivers/gpu/drm/exynos/exynos_drm_crtc.c    |   4 +-
 drivers/gpu/drm/exynos/exynos_drm_plane.c   |   3 +-
 drivers/gpu/drm/exynos/exynos_drm_plane.h   |   3 +-
 drivers/gpu/drm/i915/intel_display.c        |   4 +-
 drivers/gpu/drm/i915/intel_sprite.c         |   2 +-
 drivers/gpu/drm/imx/ipuv3-plane.c           |   3 +-
 drivers/gpu/drm/nouveau/dispnv04/overlay.c  |   6 +-
 drivers/gpu/drm/omapdrm/omap_plane.c        |   1 +
 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       |  62 ++++-
 drivers/gpu/drm/rcar-du/rcar_du_plane.c     | 196 ++++++++++++---
 drivers/gpu/drm/rcar-du/rcar_du_plane.h     |  11 +
 drivers/gpu/drm/rcar-du/rcar_du_regs.h      |   1 +
 drivers/gpu/drm/rockchip/rockchip_drm_vop.c |   5 +-
 drivers/gpu/drm/shmobile/shmob_drm_plane.c  |   3 +-
 drivers/gpu/drm/sti/sti_drm_plane.c         |   3 +-
 drivers/gpu/drm/sti/sti_hqvdp.c             |   2 +-
 include/drm/drmP.h                          |   3 +
 include/drm/drm_atomic_helper.h             |   1 +
 include/drm/drm_crtc.h                      |  48 ++++
 include/drm/drm_plane_helper.h              |   1 +
 include/uapi/drm/drm.h                      |   4 +
 include/uapi/drm/drm_mode.h                 |  32 +++
 34 files changed, 728 insertions(+), 100 deletions(-)

-- 
Regards,

Laurent Pinchart