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Date:   Mon, 29 May 2023 09:39:07 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Sakari Ailus <sakari.ailus@linux.intel.com>
Cc:     Tommaso Merciai <tomm.merciai@gmail.com>,
        jacopo.mondi@ideasonboard.com, martin.hecht@avnet.eu,
        linuxfancy@googlegroups.com,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Marco Felsch <m.felsch@pengutronix.de>,
        Gerald Loacker <gerald.loacker@wolfvision.net>,
        Krzysztof =?utf-8?Q?Ha=C5=82asa?= <khalasa@piap.pl>,
        Shawn Tu <shawnx.tu@intel.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Benjamin Mugnier <benjamin.mugnier@foss.st.com>,
        Mikhail Rudenko <mike.rudenko@gmail.com>,
        Nicholas Roth <nicholas@rothemail.net>,
        linux-media@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] media: dt-bindings: alvium: add document YAML
 binding
Message-ID: <20230529063907.GB25984@pendragon.ideasonboard.com>
References: <20230526173955.797226-1-tomm.merciai@gmail.com>
 <20230526173955.797226-2-tomm.merciai@gmail.com>
 <ZHPElYOeD2C1qo4R@kekkonen.localdomain>
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On Sun, May 28, 2023 at 09:16:05PM +0000, Sakari Ailus wrote:
> On Fri, May 26, 2023 at 07:39:43PM +0200, Tommaso Merciai wrote:
> > Add documentation of device tree in YAML schema for the ALVIUM
> > Camera from Allied Vision Inc.
> > 
> > References:
> >  - https://www.alliedvision.com/en/products/embedded-vision-solutions
> > 
> > Signed-off-by: Tommaso Merciai <tomm.merciai@gmail.com>
> > ---
> > Changes since v1:
> >  - Fixed build error as suggested by RHerring bot
> > 
> >  .../media/i2c/alliedvision,alvium.yaml        | 115 ++++++++++++++++++
> >  1 file changed, 115 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/media/i2c/alliedvision,alvium.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/media/i2c/alliedvision,alvium.yaml b/Documentation/devicetree/bindings/media/i2c/alliedvision,alvium.yaml
> > new file mode 100644
> > index 000000000000..81e9e560c99d
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/i2c/alliedvision,alvium.yaml
> > @@ -0,0 +1,115 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/media/i2c/alliedvision,alvium.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Alliedvision Alvium Camera

s/Alliedvision/Allied Vision/

> > +
> > +maintainers:
> > +  - Tommaso Merciai <tomm.merciai@gmail.com>
> > +  - Martin Hecht <martin.hecht@avnet.eu>
> > +
> > +allOf:
> > +  - $ref: /schemas/media/video-interface-devices.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    const: alliedvision,alvium

The name is very generic. There are Alvium camera modules that have a
GMSL or FPD-Link interface, and I'm pretty sure those will require a
different driver. I would add module-specific compatible strings (e.g.
"alliedvision,alvium-1500c", ...) here, with a generic fallback.
"alliedvision,alvium" isn't good as it won't cover GMSL or FPD-Link,
maybe "alliedvision,alvium-csi2" would be an option.

> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  clocks:
> > +    description: XCLK Input Clock
> > +
> > +  clock-names:
> > +    const: xclk
> 
> I'd also drop this as you have a single clock only: it's redundant.
> 
> > +
> > +  powerdown-gpios:
> > +    maxItems: 1
> > +    description: >
> > +      Reference to the GPIO connected to the powerdown pin, if any.
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> > +    description: >
> > +      Reference to the GPIO connected to the reset pin, if any.

Reading the Alvium CSI-2 Cameras User Guide, I don't see any powerdown
or reset pin on the 22-pin connector. Am I missing something ? There are
however two GPIOs (in addition to the I2C signals that are also
documented as GPIOs), do you plan to support those ?

> > +
> > +  streamon-delay:
> > +    maxItems: 1
> > +    description: >
> > +      Delay before camera start capturing frames in us.

Add "-us" to the property name to indicate the unit.

This is a vendor-specific property, and should thus have a vendor
prefix.

A longer description is needed, from that single line I have no idea
what the property does exactly.

> > +
> > +  rotation:
> > +    enum:
> > +      - 0
> > +      - 180

Why is the rotation restricted to 0 or 180 ? Someone could mount the
module with  90 degrees rotation, shouldn't the DT bindings allow
describing that ?

You need a property for the vcc-ext-in supply.

> > +
> > +  port:
> > +    description: Digital Output Port
> > +    $ref: /schemas/graph.yaml#/$defs/port-base
> > +    additionalProperties: false
> > +
> > +    properties:
> > +      endpoint:
> > +        $ref: /schemas/media/video-interfaces.yaml#
> > +        unevaluatedProperties: false
> > +
> > +        properties:
> > +          clock-lanes:
> > +            const: 0
> 
> The driver can know this, no need to have it in DT, i.e. please drop it.
> 
> > +          data-lanes:
> > +            minItems: 1
> > +            maxItems: 4
> > +          link-frequencies: true
> > +
> > +        required:
> > +          - data-lanes
> > +          - link-frequencies
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - clocks
> > +  - clock-names
> > +  - port
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +      #include <dt-bindings/gpio/gpio.h>
> > +      #include <dt-bindings/clock/imx8mp-clock.h>
> > +
> > +      i2c {
> > +          #address-cells = <1>;
> > +          #size-cells = <0>;
> > +
> > +          camera: alvium@3c {
> > +              compatible = "alliedvision,alvium";

The "alliedvision" prefix is missing from
Documentation/devicetree/bindings/vendor-prefixes.yaml.

> > +              pinctrl-names = "default";
> > +              pinctrl-0 = <&pinctrl_csi0_pwn>, <&pinctrl_csi0_rst>, <&pinctrl_csi_mclk>;

I'd drop pinctrl, it makes the example longer without adding much value.

> > +              reg = <0x3c>;
> > +              clocks = <&clk IMX8MP_CLK_IPP_DO_CLKO2>;
> > +              clock-names = "xclk";
> > +              assigned-clocks = <&clk IMX8MP_CLK_IPP_DO_CLKO2>;
> > +              assigned-clock-parents = <&clk IMX8MP_CLK_24M>;
> > +              assigned-clock-rates = <24000000>;
> > +              streamon-delay = <20>;
> > +              powerdown-gpios = <&gpio2 11 GPIO_ACTIVE_HIGH>;
> > +              reset-gpios = <&gpio1 6 GPIO_ACTIVE_LOW>;
> > +              status = "okay";
> > +
> > +              port {
> > +                  alvium_out: endpoint {
> > +                      remote-endpoint = <&mipi_csi_0_in>;
> > +                      data-lanes = <1 2 3 4>;
> > +                      link-frequencies = /bits/ 64 <681250000>;
> > +                      clock-lanes = <0>;
> > +                  };
> > +              };
> > +          };
> > +      };
> > +
> > +...

-- 
Regards,

Laurent Pinchart