• Niklas Söderlund's avatar
    media: rcar-{csi2,vin}: Move to full Virtual Channel routing per CSI-2 IP · 3e52419e
    Niklas Söderlund authored
    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: default avatarNiklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
    Tested-by: default avatarJacopo Mondi <jacopo+renesas@jmondi.org>
    Signed-off-by: default avatarHans Verkuil <hverkuil-cisco@xs4all.nl>
    [hverkuil: fix two trivial checkpatch whitespace issues]
    3e52419e
rcar-vin.h 7.92 KB