Re: [PATCH 07/14] dt-bindings: media: i2c: Add A31 MIPI CSI-2 bindings documentation

[Maxime Ripard <maxime@cerno.tech>]

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On Wed, Nov 04, 2020 at 11:48:27AM +0100, Paul Kocialkowski wrote:
> Hi,
> 
> On Tue 27 Oct 20, 19:44, Maxime Ripard wrote:
> > On Tue, Oct 27, 2020 at 10:52:21AM +0100, Paul Kocialkowski wrote:
> > > Hi,
> > > 
> > > On Mon 26 Oct 20, 17:14, Maxime Ripard wrote:
> > > > i2c? :)
> > > 
> > > Oops, good catch!
> > >  
> > > > On Fri, Oct 23, 2020 at 07:45:39PM +0200, Paul Kocialkowski wrote:
> > > > > This introduces YAML bindings documentation for the A31 MIPI CSI-2
> > > > > controller.
> > > > > 
> > > > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > > > > ---
> > > > >  .../media/allwinner,sun6i-a31-mipi-csi2.yaml  | 168 ++++++++++++++++++
> > > > >  1 file changed, 168 insertions(+)
> > > > >  create mode 100644 Documentation/devicetree/bindings/media/allwinner,sun6i-a31-mipi-csi2.yaml
> > > > > 
> > > > > diff --git a/Documentation/devicetree/bindings/media/allwinner,sun6i-a31-mipi-csi2.yaml b/Documentation/devicetree/bindings/media/allwinner,sun6i-a31-mipi-csi2.yaml
> > > > > new file mode 100644
> > > > > index 000000000000..9adc0bc27033
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/media/allwinner,sun6i-a31-mipi-csi2.yaml
> > > > > @@ -0,0 +1,168 @@
> > > > > +# SPDX-License-Identifier: GPL-2.0
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +$id: http://devicetree.org/schemas/media/allwinner,sun6i-a31-mipi-csi2.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: Allwinner A31 MIPI CSI-2 Device Tree Bindings
> > > > > +
> > > > > +maintainers:
> > > > > +  - Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > > > > +
> > > > > +properties:
> > > > > +  compatible:
> > > > > +    oneOf:
> > > > > +      - const: allwinner,sun6i-a31-mipi-csi2
> > > > > +      - items:
> > > > > +          - const: allwinner,sun8i-v3s-mipi-csi2
> > > > > +          - const: allwinner,sun6i-a31-mipi-csi2
> > > > > +
> > > > > +  reg:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  interrupts:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  clocks:
> > > > > +    items:
> > > > > +      - description: Bus Clock
> > > > > +      - description: Module Clock
> > > > > +
> > > > > +  clock-names:
> > > > > +    items:
> > > > > +      - const: bus
> > > > > +      - const: mod
> > > > > +
> > > > > +  phys:
> > > > > +    items:
> > > > > +      - description: MIPI D-PHY
> > > > > +
> > > > > +  phy-names:
> > > > > +    items:
> > > > > +      - const: dphy
> > > > > +
> > > > > +  resets:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  # See ./video-interfaces.txt for details
> > > > > +  ports:
> > > > > +    type: object
> > > > > +
> > > > > +    properties:
> > > > > +      port@0:
> > > > > +        type: object
> > > > > +        description: Input port, connect to a MIPI CSI-2 sensor
> > > > > +
> > > > > +        properties:
> > > > > +          reg:
> > > > > +            const: 0
> > > > > +
> > > > > +          endpoint:
> > > > > +            type: object
> > > > > +
> > > > > +            properties:
> > > > > +              remote-endpoint: true
> > > > > +
> > > > > +              bus-type:
> > > > > +                const: 4
> > > > > +
> > > > > +              clock-lanes:
> > > > > +                maxItems: 1
> > > > > +
> > > > > +              data-lanes:
> > > > > +                minItems: 1
> > > > > +                maxItems: 4
> > > > > +
> > > > > +            required:
> > > > > +              - bus-type
> > > > > +              - data-lanes
> > > > > +              - remote-endpoint
> > > > > +
> > > > > +            additionalProperties: false
> > > > > +
> > > > > +        required:
> > > > > +          - endpoint
> > > > > +
> > > > > +        additionalProperties: false
> > > > > +
> > > > > +      port@1:
> > > > > +        type: object
> > > > > +        description: Output port, connect to a CSI controller
> > > > > +
> > > > > +        properties:
> > > > > +          reg:
> > > > > +            const: 1
> > > > > +
> > > > > +          endpoint:
> > > > > +            type: object
> > > > > +
> > > > > +            properties:
> > > > > +              remote-endpoint: true
> > > > > +
> > > > > +              bus-type:
> > > > > +                const: 4
> > > > 
> > > > That one seems a bit weird. If the input and output ports are using the
> > > > same format, what is that "bridge" supposed to be doing?
> > > 
> > > Fair enough. What this represents is the internal link (likely a FIFO) between
> > > the two controllers. It is definitely not a MIPI CSI-2 bus but there's no
> > > mbus type for an internal link (probably because it's not a bus after all).
> > > 
> > > Note that on the CSI controller side, we need the bus-type to be set to 4 for it
> > > to properly select the MIPI CSI-2 input. So it just felt more logical to have
> > > the same on the other side of the endpoint. On the other hand, we can just
> > > remove it on the MIPI CSI-2 controller side since it won't check it and have it
> > > fallback to the unknown mbus type.
> > > 
> > > But that would make the types inconsistent on the two sides of the link.
> > > I don't think V4L2 will complain about it at the moment, but it would also make
> > > sense that it does eventually.
> > > 
> > > What do you think?
> > 
> > There's still the same issue though, it doesn't make any sense that a
> > bridge doesn't change the bus type. If it really did, we wouldn't need
> > that in the first place.
> 
> Yes I agreee.
> 
> > What you want to check in your driver is whether the subdev you're
> > connected to has a sink pad that uses MIPI-CSI
> 
> I'm not really sure that's possible, but if it is it would indeed be the most
> appropriate solution. If it's not, we still need to know that we need to feed
> from MIPI CSI-2 so I don't see any other option than report MIPI CSI-2 on both
> ends of MIPI CSI-2 controller.
> 
> But there's still the question of what media bus type should be reported for
> the CSI <-> MIPI CSI-2 link. I'm fine with unknown but we could also add a
> generic internal bus type for this case.

I guess both questions would need to be discussed more on the v4l2 side.

Maxime

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