The A83T supports MIPI CSI-2 with a composite controller, covering
both the protocol logic and the D-PHY implementation. This controller
seems to be found on the A83T only and probably was abandoned since.

This implementation splits the protocol and D-PHY registers and
uses the PHY framework internally. The D-PHY is not registered as a
standalone PHY driver since it cannot be used with any other
controller.

There are a few notable points about the controller:
- The initialisation sequence involes writing specific magic init
  values that do not seem to make any particular sense given the
  concerned register fields;
- Interrupts appear to be hitting regardless of the interrupt mask
  registers, which can cause a serious flood when transmission errors
  occur.

Only 8-bit and 10-bit Bayer formats are currently supported.
While up to 4 internal channels to the CSI controller exist, only one
is currently supported by this implementation.

This work is based on the first version of the driver submitted by
Kévin L'hôpital, which was adapted to mainline from the Allwinner BSP.
This version integrates MIPI CSI-2 support as a standalone V4L2 subdev
instead of merging it in the sun6i-csi driver.

It was tested on a Banana Pi M3 board with an OV8865 sensor in a 4-lane
configuration.
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>