Date:   Wed, 4 Nov 2020 11:26:43 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Maxime Ripard <mripard@...nel.org>, kevin.lhopital@...mail.com,
        Kévin L'hôpital <kevin.lhopital@...tlin.com>
Subject: Re: [PATCH 1/3] dt-bindings: media: i2c: Add OV8865 bindings
 documentation

Hi Sakari and thanks for the review!

On Tue 03 Nov 20, 01:24, Sakari Ailus wrote:
> On Fri, Oct 23, 2020 at 07:54:04PM +0200, Paul Kocialkowski wrote:
> > This introduces YAML bindings documentation for the OV8865
> > image sensor.
> > 
> > Co-developed-by: Kévin L'hôpital <kevin.lhopital@...tlin.com>
> > Signed-off-by: Kévin L'hôpital <kevin.lhopital@...tlin.com>
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > ---
> >  .../bindings/media/i2c/ovti,ov8865.yaml       | 124 ++++++++++++++++++
> >  1 file changed, 124 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/media/i2c/ovti,ov8865.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/media/i2c/ovti,ov8865.yaml b/Documentation/devicetree/bindings/media/i2c/ovti,ov8865.yaml
> > new file mode 100644
> > index 000000000000..807f1a94afae
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/i2c/ovti,ov8865.yaml
> > @@ -0,0 +1,124 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/media/i2c/ovti,ov8865.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: OmniVision OV8865 Image Sensor Device Tree Bindings
> > +
> > +maintainers:
> > +  - Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > +
> > +properties:
> > +  compatible:
> > +    const: ovti,ov8865
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  clocks:
> > +    items:
> > +      - description: EXTCLK Clock
> > +
> > +  clock-names:
> > +    items:
> > +      - const: extclk
> 
> Is this needed with a single clock?

Yes I think so: we grab the clock with devm_clk_get which takes a name string
that matches the clock-names property.

> And... shouldn't this also come with assigned-clock-rates etc., to set the
> clock frequency?

I'm a bit confused why we would need to do that in the device-tree rather than
setting the clock rate with clk_set_rate in the driver, like any other driver
does. I think this was discussed before (on the initial ov8865 series) and the
conclusion was that there is no particular reason for media i2c drivers to
behave differently. So I believe this is the correct approach.

> > +
> > +  dvdd-supply:
> > +    description: Digital Domain Power Supply
> > +
> > +  avdd-supply:
> > +    description: Analog Domain Power Supply (internal AVDD is used if missing)
> > +
> > +  dovdd-supply:
> > +    description: I/O Domain Power Supply
> > +
> > +  powerdown-gpios:
> > +    maxItems: 1
> > +    description: Power Down Pin GPIO Control (active low)
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> > +    description: Reset Pin GPIO Control (active low)
> > +
> > +  port:
> > +    type: object
> > +    description: Input port, connect to a MIPI CSI-2 receiver
> > +
> > +    properties:
> > +      endpoint:
> > +        type: object
> > +
> > +        properties:
> > +          remote-endpoint: true
> > +
> > +          bus-type:
> > +            const: 4
> > +
> > +          clock-lanes:
> > +            maxItems: 1
> 
> I believe you can drop clock-lanes and bus-type; these are both constants.

I don't understand why bus-type should be dropped because it is constant:
if bus-type is set to something else, the driver will definitely not probe
since we're requesting V4L2_MBUS_CSI2_DPHY for v4l2_fwnode_endpoint_parse.
So I think it's quite important for the bindings to reflect this.

> I presume the device does not support lane remapping?

That's correct so this is indeed not something we can configure.
But shouldn't we instead specift clock-lanes = <0> as a const rather than
getting rid of it?

> Could you also add link-frequencies, to list which frequencies are known to
> be good?

Ah right, I had missed it. I'm a bit unsure about what I should do with the
information from the driver though: should I refuse to use link frequencies that
are not in the list?

Cheers,

Paul

> Same comments on the other OV sensor bindings.
> 
> > +
> > +          data-lanes:
> > +            minItems: 1
> > +            maxItems: 4
> > +
> > +        required:
> > +          - bus-type
> > +          - data-lanes
> > +          - remote-endpoint
> > +
> > +        additionalProperties: false
> > +
> > +    required:
> > +      - endpoint
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - clocks
> > +  - clock-names
> > +  - dvdd-supply
> > +  - dovdd-supply
> > +  - port
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/clock/sun8i-a83t-ccu.h>
> > +    #include <dt-bindings/gpio/gpio.h>
> > +
> > +    i2c2 {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        ov8865: camera@36 {
> > +            compatible = "ovti,ov8865";
> > +            reg = <0x36>;
> > +
> > +            pinctrl-names = "default";
> > +            pinctrl-0 = <&csi_mclk_pin>;
> > +
> > +            clocks = <&ccu CLK_CSI_MCLK>;
> > +            clock-names = "extclk";
> > +
> > +            avdd-supply = <&reg_ov8865_avdd>;
> > +            dovdd-supply = <&reg_ov8865_dovdd>;
> > +            dvdd-supply = <&reg_ov8865_dvdd>;
> > +
> > +            powerdown-gpios = <&pio 4 17 GPIO_ACTIVE_LOW>; /* PE17 */
> > +            reset-gpios = <&pio 4 16 GPIO_ACTIVE_LOW>; /* PE16 */
> > +
> > +            port {
> > +                ov8865_out_mipi_csi2: endpoint {
> > +                    bus-type = <4>; /* MIPI CSI-2 D-PHY */
> > +                    clock-lanes = <0>;
> > +                    data-lanes = <1 2 3 4>;
> > +
> > +                    remote-endpoint = <&mipi_csi2_in_ov8865>;
> > +                };
> > +            };
> > +        };
> > +    };
> > +
> > +...
> 
> -- 
> Regards,
> 
> Sakari Ailus

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

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