When Gen3 support was first added to this R-Car VIN and CSI-2 driver the
routing was centred around the CHSEL register which multiplexes the
different parallel buses that sit between the CSI-2 receivers source
side and the VIN dma engines. This was a bad design as the multiplexing
do allow for only a few combinations and do not play nice with many
video streams in the system.

For example it's only possible for CSI-2 Virtual Channels 0 and 1 of any
given CSI-2 receiver to be used together with the scaler.

Later datasheets have expanded the documentation and it is now possible
to improve on this design by allowing any Virtual Channel to be routed
to any R-Car VIN instance, provided that there exists a parallel bus
between them. This increases the flexibility as all Virtual Channels can
now be used together with the scaler for example.

The redesign is not however perfect. While the new design allows for
many more routes, two constrains limit a small portion of routes that
was possible in the old design but are no more.

- It is no longer possible to route the same CSI-2 and VC to more then
  one VIN at a time. This was theoretically possible before if the
  specific SoC allowed for the same CSI-2 and VC to be routed to two
  different VIN capture groups.

- It is no longer possible to simultaneously mix links from two CSI-2 IP
  blocks to the same VIN capture group.

  For example if VIN2 is capturing from CSI40 then VIN{0,1,3} must also
  capture from CSI40. While VIN{4,5,6,7} is still free to capture from
  any other CSI-2 IP in the system. Once all VIN{0,1,2,3} links to CSI40
  are disabled that VIN capture group is free again to capture from any
  other CSI-2 IP it is connected to.

At the core of the redesign is greater cooperator of the R-Car VIN and
CSI-2 drivers in configuring the routing. The VIN driver is after this
change only responsible to configure the full VIN capture groups
parallel buses to be to a particular CSI-2 IP. While the configuration
of which CSI-2 Virtual Channel is outputted on which of the R-Car CSI-2
IP output ports is handled by the CSI-2 driver.

Before this change the CSI-2 Virtual Channel to output port was static
in the CSI-2 driver and the different links only manipulated the VIN
capture groups CHSEL register. With this change both the CHSEl register
and the CSI-2 routing VCDT registers are modified for greater
flexibility.

This change touches both the R-Car VIN and R-Car CSI-2 drivers in the
same commit as both drivers cooperate closely and one change without the
other would more or less break video capture.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: fix two trivial checkpatch whitespace issues]