[RFC,0/3] Add support for BCM2835 camera interface (unicam)

Hello !

This patch series adds the BCM2835 CCP2/CSI2 camera interface named
unicam. This driver is already used in the out-of-tree linux-rpi
repository [1], and this work aims to support it in mainline.

The series is based on top of:
- Rebased on top of 5.16 Tomi Valkeinen's multiplexed stream work, on
  his multistream/work branch [2] which has been submitted as v10 at the
  time of this writing. The objective is to demonstrate the use of
  multiplexed streams on a real world widely used example as well as
  supporting unicam mainline.
- "Add 12bit and 14bit luma-only formats" series [3].

The series is made of 4 patches:
- 2/3 introduces dt-bindings documentation and MAINTAINERS entry
  I have tentatively assigned maintainership, is this fine ?
- 2/3 adds the driver support in media/platform
- 3/3 modifies imx219 driver to make it use the multiplexed streams API

All those patches are in my tree [4].

Patch 2/3 comes from the linux-rpi work [1] with substantial
modifications:
- Removed the non-mc API which is deprecated, and not needed upstream
- Moved from one video node with two source pads (image and embedded) to
  two video nodes
- Added a subdev between the sensor and the video nodes to properly
  route the streams
- Added support for multiplexed streams API

In order to test it, one will need a RPi board and the camv2 (imx219)
sensor.  An updated v4l-utils is also needed [5] to have support for
multiplexed streams.

v4l2-compliance passes on both video devices, without streaming testing
though.

The downstream DTB's and overlays are used from the existing Raspberry
Pi OS for testing, and this series does not yet integrate the device
tree nodes into the upstream BCM2835 or BCM2711 device tree support.

The media-ctl topology is:
```
pi@raspberrypi:~ $ media-ctl -d0 -p
Media controller API version 5.16.0

Media device information
------------------------
driver          unicam
model           unicam
serial          
bus info        platform:fe801000.csi
hw revision     0x0
driver version  5.16.0

Device topology
- entity 1: unicam-subdev (3 pads, 3 links, 1 route)
            type V4L2 subdev subtype Unknown flags 0
            device node name /dev/v4l-subdev0
	routes:
		0/0 -> 1/0 [ACTIVE]
	pad0: Sink
		[stream:0 fmt:UYVY8_2X8/640x480 field:none colorspace:srgb xfer:srgb ycbcr:601 quantization:lim-range]
		<- "imx219 10-0010":0 [ENABLED,IMMUTABLE]
	pad1: Source
		[stream:0 fmt:UYVY8_2X8/640x480 field:none colorspace:srgb xfer:srgb ycbcr:601 quantization:lim-range]
		-> "unicam-image":0 [ENABLED,IMMUTABLE]
	pad2: Source
		-> "unicam-embedded":0 [ENABLED,IMMUTABLE]

- entity 5: imx219 10-0010 (1 pad, 1 link, 2 routes)
            type V4L2 subdev subtype Sensor flags 0
            device node name /dev/v4l-subdev1
	routes:
		0/0 -> 0/0 [ACTIVE, IMMUTABLE, SOURCE]
		0/0 -> 0/1 [ACTIVE, SOURCE]
	pad0: Source
		[stream:0 fmt:SRGGB10_1X10/3280x2464 field:none colorspace:raw
		crop.bounds:(8,8)/3280x2464
		crop:(8,8)/3280x2464]
		[stream:1 fmt:METADATA_8/16384x1 field:none
		crop.bounds:(8,8)/3280x2464
		crop:(8,8)/3280x2464]
		-> "unicam-subdev":0 [ENABLED,IMMUTABLE]

- entity 7: unicam-image (1 pad, 1 link, 0 route)
            type Node subtype V4L flags 1
            device node name /dev/video0
	pad0: Sink
		<- "unicam-subdev":1 [ENABLED,IMMUTABLE]

- entity 13: unicam-embedded (1 pad, 1 link, 0 route)
             type Node subtype V4L flags 0
             device node name /dev/video1
	pad0: Sink
		<- "unicam-subdev":2 [ENABLED,IMMUTABLE]
```

In order to properly configure the media pipeline, it is needed to call
the usual ioctls, and configure routing in order to send the embedded
data from the sensor to the "unicam-embedded" device node :

``` media=0
media-ctl -d${media} -l "'imx219 10-0010':0->'unicam-subdev':0 [1]"
media-ctl -d${media} -l "'unicam-subdev':1->'unicam-image':0 [1]"
media-ctl -d${media} -v -R "'unicam-subdev' [0/0->1/0[1],0/1->2/0[1]]"
media-ctl -d${media} -V "'imx219 10-0010':0/0
[fmt:SRGGB10_1X10/3280x2464 field:none]" v4l2-ctl -d0 --set-fmt-video
width=3280,height=2464,pixelformat='pRAA',field=none media-ctl
-d${media} -v -V "'imx219 10-0010':0/1 [fmt:METADATA_8/16384x1
field:none]" media-ctl -d${media} -p ```

Be sure to configure the routes before setting the format, as s_routing
resets the default format.

Then a frame can be capture with yavta:
`yavta --capture=1 /dev/video0 -F/tmp/test-#.bin`


[1]: https://github.com/raspberrypi/linux/tree/rpi-5.15.y
[2]: https://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux.git/log/?h=multistream/work
[3]: https://patchwork.linuxtv.org/project/linux-media/list/?series=7099
[4]: https://github.com/jhautbois/linux-rpi/tree/jmh/tomba/multistream/work-v10
[5]: https://github.com/tomba/v4l-utils

Jean-Michel Hautbois (3):
  media: dt-bindings: media: Add bindings for bcm2835-unicam
  media: bcm2835-unicam: Add support for for CCP2/CSI2 camera interface
  media: imx219: Add support for multiplexed streams

 .../bindings/media/brcm,bcm2835-unicam.yaml   |  103 +
 MAINTAINERS                                   |    7 +
 drivers/media/i2c/imx219.c                    |  458 +--
 drivers/media/platform/Kconfig                |    1 +
 drivers/media/platform/Makefile               |    2 +
 drivers/media/platform/bcm2835/Kconfig        |   21 +
 drivers/media/platform/bcm2835/Makefile       |    3 +
 .../media/platform/bcm2835/bcm2835-unicam.c   | 2694 +++++++++++++++++
 .../media/platform/bcm2835/vc4-regs-unicam.h  |  253 ++
 9 files changed, 3332 insertions(+), 210 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/media/brcm,bcm2835-unicam.yaml
 create mode 100644 drivers/media/platform/bcm2835/Kconfig
 create mode 100644 drivers/media/platform/bcm2835/Makefile
 create mode 100644 drivers/media/platform/bcm2835/bcm2835-unicam.c
 create mode 100644 drivers/media/platform/bcm2835/vc4-regs-unicam.h