media: cedrus: Update TODO with future rework plans

The current TODO list of the cedrus driver is now outdated as most of the
points it mentions were already tackled. In addition it is no longer
considered relevant to wait for a stateless encoder driver to move it out
of staging. The hantro/verisilicon driver was already unstaged without this
condition.

However the driver suffers from a bad initial design that showed to be very
limiting. It was also not a very good fit for a video codec driver either.

Since a rework of the driver was already carried out for the purpose of
adding encoding support, update the TODO list with a description of the
rework. This reworked driver will be published soon and transitional
commits from the current driver will be submitted upstreamer after that.

It seems best to wait for the rework to land upstream before unstaging the
driver, since a major rework is best operated on a staging driver instead
of a fully upstream one.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

media: cedrus: Remove completed item from TODO list (dma-buf references)

Access to reference frames that were imported from dma-buf was taken
care of and is no longer a pending item on the driver's TODO list.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

media: cedrus: add action item to the TODO

Mention that the request validation should increment the memory refcount
of reference buffers so we don't forget to do this.

Acked-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

media: platform: Add Cedrus VPU decoder driver

This introduces the Cedrus VPU driver that supports the VPU found in
Allwinner SoCs, also known as Video Engine. It is implemented through
a V4L2 M2M decoder device and a media device (used for media requests).
So far, it only supports MPEG-2 decoding.

Since this VPU is stateless, synchronization with media requests is
required in order to ensure consistency between frame headers that
contain metadata about the frame to process and the raw slice data that
is used to generate the frame.

This driver was made possible thanks to the long-standing effort
carried out by the linux-sunxi community in the interest of reverse
engineering, documenting and implementing support for the Allwinner VPU.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
[hans.verkuil@cisco.com: dropped obsolete MEDIA_REQUEST_API from Kconfig]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>