The A31 CSI controller supports a MIPI CSI-2 bridge input, which has
its own dedicated port in the fwnode graph.

Support for this input is added with this change:
- two pads are defined for the media entity instead of one
  and only one needs to be connected at a time;
- the pads currently match the fwnode graph representation;
- links are created between our pads and the subdevs for each
  interface and are no longer immutable so that userspace can select
  which interface to use in case both are bound to a subdev;
- fwnode endpoints are parsed and stored for each interface;
- the active subdev (and fwnode endpoint) is retrieved when validating
  the media link at stream on time and cleared at stream off;
- an error is raised if both links are active at the same time;
- the MIPI interface bit is set if the MIPI CSI-2 bridge endpoint is
  active.

In the future, the media entity representation might evolve to:
- distinguish the internal parallel bridge and data formatter;
- represent each of the 4 internal channels that can exist between
  the parallel bridge (for BT656 time-multiplex) and MIPI CSI-2
  (internal channels can be mapped to virtual channels);
- connect the controller's output to the ISP instead of its
  DMA engine.

Finally note that the MIPI CSI-2 bridges should not be linked in
the fwnode graph unless they have a sensor subdev attached.

Signed-off-by: Paul Kocialkowski <redacted>
---
 .../platform/sunxi/sun6i-csi/sun6i_csi.c      | 123 ++++++++++++++----
 .../platform/sunxi/sun6i-csi/sun6i_csi.h      |   3 -
 .../platform/sunxi/sun6i-csi/sun6i_video.c    |  53 ++++----
 .../platform/sunxi/sun6i-csi/sun6i_video.h    |   7 +-
 4 files changed, 135 insertions(+), 51 deletions(-)

diff --git a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
index f1150de94e98..481181038e1e 100644
--- a/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c
+++ b/drivers/media/platform/sunxi/sun6i-csi/sun6i_csi.c

@@ -52,15 +52,16 @@ bool sun6i_csi_is_format_supported(struct sun6i_csi *csi,
 				   u32 pixformat, u32 mbus_code)
 {
 	struct sun6i_csi_dev *sdev = sun6i_csi_to_dev(csi);
+	struct v4l2_fwnode_endpoint *endpoint = sdev->csi.video.source_endpoint;
 
 	/*
 	 * Some video receivers have the ability to be compatible with
 	 * 8bit and 16bit bus width.
 	 * Identify the media bus format from device tree.
 	 */
-	if ((sdev->csi.v4l2_ep.bus_type == V4L2_MBUS_PARALLEL
-	     || sdev->csi.v4l2_ep.bus_type == V4L2_MBUS_BT656)
-	     && sdev->csi.v4l2_ep.bus.parallel.bus_width == 16) {
+	if ((endpoint->bus_type == V4L2_MBUS_PARALLEL
+	     || endpoint->bus_type == V4L2_MBUS_BT656)
+	     && endpoint->bus.parallel.bus_width == 16) {