Re: [PATCH v2 61/66] dt-bindings: media: Add Allwinner A31 ISP bindings documentation

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

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Hi Laurent,

On Mon 14 Feb 22, 19:09, Laurent Pinchart wrote:
> Hi Paul,
> 
> On Mon, Feb 14, 2022 at 05:18:07PM +0100, Paul Kocialkowski wrote:
> > On Mon 07 Feb 22, 17:51, Laurent Pinchart wrote:
> > > On Sat, Feb 05, 2022 at 07:54:24PM +0100, Paul Kocialkowski wrote:
> > > > This introduces YAML bindings documentation for the Allwinner A31 Image
> > > > Signal Processor (ISP).
> > > > 
> > > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > > > ---
> > > >  .../media/allwinner,sun6i-a31-isp.yaml        | 117 ++++++++++++++++++
> > > >  1 file changed, 117 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/media/allwinner,sun6i-a31-isp.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/media/allwinner,sun6i-a31-isp.yaml b/Documentation/devicetree/bindings/media/allwinner,sun6i-a31-isp.yaml
> > > > new file mode 100644
> > > > index 000000000000..2d87022c43ce
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/media/allwinner,sun6i-a31-isp.yaml
> > > > @@ -0,0 +1,117 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/media/allwinner,sun6i-a31-isp.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Allwinner A31 Image Signal Processor Driver (ISP) Device Tree Bindings
> > > > +
> > > > +maintainers:
> > > > +  - Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    enum:
> > > > +      - allwinner,sun6i-a31-isp
> > > > +      - allwinner,sun8i-v3s-isp
> > > > +
> > > > +  reg:
> > > > +    maxItems: 1
> > > > +
> > > > +  interrupts:
> > > > +    maxItems: 1
> > > > +
> > > > +  clocks:
> > > > +    items:
> > > > +      - description: Bus Clock
> > > > +      - description: Module Clock
> > > > +      - description: DRAM Clock
> > > 
> > > That's interesting, does the ISP have a dedicated DRAM ?
> > 
> > It doesn't, it actually uses the main DRAM with the "mbus" interconnect.
> > The clock is probably for the DMA engine.
> > 
> > > > +
> > > > +  clock-names:
> > > > +    items:
> > > > +      - const: bus
> > > > +      - const: mod
> > > > +      - const: ram
> > > > +
> > > > +  resets:
> > > > +    maxItems: 1
> > > > +
> > > > +  ports:
> > > > +    $ref: /schemas/graph.yaml#/properties/ports
> > > > +
> > > > +    properties:
> > > > +      port@0:
> > > > +        $ref: /schemas/graph.yaml#/$defs/port-base
> > > > +        description: CSI0 input port
> > > > +
> > > > +        properties:
> > > > +          reg:
> > > > +            const: 0
> > > > +
> > > > +          endpoint:
> > > > +            $ref: video-interfaces.yaml#
> > > > +            unevaluatedProperties: false
> > > 
> > > If no other property than remote-endpoint are allowed, I'd write
> > > 
> > >           endpoint:
> > >             $ref: video-interfaces.yaml#
> > > 	    remote-endpoint: true
> > >             additionalProperties: false
> > > 
> > > Same below.
> > > 
> > > > +
> > > > +        additionalProperties: false
> > > > +
> > > > +      port@1:
> > > > +        $ref: /schemas/graph.yaml#/$defs/port-base
> > > > +        description: CSI1 input port
> > > > +
> > > > +        properties:
> > > > +          reg:
> > > > +            const: 0
> > > 
> > > This should be 1.
> > 
> > Correct, thanks!
> > 
> > > > +
> > > > +          endpoint:
> > > > +            $ref: video-interfaces.yaml#
> > > > +            unevaluatedProperties: false
> > > > +
> > > > +        additionalProperties: false
> > > > +
> > > > +    anyOf:
> > > > +      - required:
> > > > +        - port@0
> > > > +      - required:
> > > > +        - port@1
> > > 
> > > As ports are an intrinsic property of the ISP, both should be required,
> > > but they don't have to be connected.
> > 
> > Well the ISP does have the ability to source from either CSI0 and CSI1
> > but I don't really get the point of declaring both ports when only one
> > of the two controllers is present.
> 
> If it's within an SoC I don't mind too much. What I usually insist on is
> declaring all ports even when no external devices are connected on the
> board. It may however be easier to implement things on the driver side
> when all the ports are declared, even for internal devices. I won't
> insist either way here.
> 
> > > By the way, how do you select at runtime which CSI-2 RX the ISP gets its
> > > image stream from ? Is it configured through registers of the ISP ?
> > 
> > Actually what the ISP gets is fully dependent on what is received by the
> > CSI controller it is connected to (which can be the mipi csi-2 controller
> > or its direct parallel pins), so the configuration happens on the CSI side.
> 
> OK, then how do you select at runtime which CSI the ISP gets its image
> stream from ? :-)

What is done in the driver is that all available csi(s) entities pads are linked
to a single csi sink media pad, which allows userspace to enable one or the
other. If there's only one, it's enabled by default.

The actual stream source (isp_dev->proc.source) is selected at link_validate
time and the source bit is set in sun6i_isp_proc_enable.

I hope this answers your question!

Thanks,

Paul

> > > > +
> > > > +required:
> > > > +  - compatible
> > > > +  - reg
> > > > +  - interrupts
> > > > +  - clocks
> > > > +  - clock-names
> > > > +  - resets
> > > > +
> > > > +additionalProperties: false
> > > > +
> > > > +examples:
> > > > +  - |
> > > > +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> > > > +    #include <dt-bindings/clock/sun8i-v3s-ccu.h>
> > > > +    #include <dt-bindings/reset/sun8i-v3s-ccu.h>
> > > > +
> > > > +    isp: isp@1cb8000 {
> > > > +        compatible = "allwinner,sun8i-v3s-isp";
> > > > +        reg = <0x01cb8000 0x1000>;
> > > > +        interrupts = <GIC_SPI 83 IRQ_TYPE_LEVEL_HIGH>;
> > > > +        clocks = <&ccu CLK_BUS_CSI>,
> > > > +             <&ccu CLK_CSI1_SCLK>,
> > > > +             <&ccu CLK_DRAM_CSI>;
> > > > +        clock-names = "bus", "mod", "ram";
> > > > +        resets = <&ccu RST_BUS_CSI>;
> > > > +
> > > > +        ports {
> > > > +            #address-cells = <1>;
> > > > +            #size-cells = <0>;
> > > > +
> > > > +            port@0 {
> > > > +                reg = <0>;
> > > > +
> > > > +                isp_in_csi0: endpoint {
> > > > +                    remote-endpoint = <&csi0_out_isp>;
> > > > +                };
> > > > +            };
> > > > +        };
> > > > +    };
> > > > +
> > > > +...
> 
> -- 
> Regards,
> 
> Laurent Pinchart

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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