linux-kernel - Re: [PATCH v4 2/2] media: dt-bindings: media: st,stm32-dcmi: Add support of BT656

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Date:   Wed, 21 Oct 2020 16:00:33 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Hugues Fruchet <hugues.fruchet@...com>
Cc:     Alexandre Torgue <alexandre.torgue@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        Alain Volmat <alain.volmat@...com>,
        Yannick Fertre <yannick.fertre@...com>,
        Philippe CORNU <philippe.cornu@...com>
Subject: Re: [PATCH v4 2/2] media: dt-bindings: media: st,stm32-dcmi: Add
 support of BT656

Hi Hugues,

On Tue, Oct 20, 2020 at 12:14:49PM +0200, Hugues Fruchet wrote:
> Add support of BT656 parallel bus mode in DCMI.
> This mode is enabled when hsync-active & vsync-active
> fields are not specified.
> 
> Signed-off-by: Hugues Fruchet <hugues.fruchet@...com>
> ---
>  .../devicetree/bindings/media/st,stm32-dcmi.yaml   | 30 ++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
> index 3fe778c..1ee521a 100644
> --- a/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
> +++ b/Documentation/devicetree/bindings/media/st,stm32-dcmi.yaml
> @@ -44,6 +44,36 @@ properties:
>        bindings defined in
>        Documentation/devicetree/bindings/media/video-interfaces.txt.
>  
> +    properties:
> +      endpoint:
> +        type: object
> +
> +        properties:
> +          bus-width: true
> +
> +          hsync-active:
> +            description:
> +              If both HSYNC and VSYNC polarities are not specified, BT656
> +              embedded synchronization is selected.
> +            default: 0
> +
> +          vsync-active:
> +            description:
> +              If both HSYNC and VSYNC polarities are not specified, BT656
> +              embedded synchronization is selected.
> +            default: 0

Should I understand this as if the polarities were not specified, BT.656
will be used? The bindings previously documented BT.601 (parallel) only, so
it was somewhat ambigious to begin with. Is there a risk of interpreting
old BT.601 bindings as BT.656? With bus-type property, I believe you could
avoid at least that risk.

Also not specifying at least one of the default values leads to BT.656
without bus-type. That could be addressed by removing the defaults.

> +
> +          pclk-sample: true
> +
> +          remote-endpoint: true
> +
> +        required:
> +          - remote-endpoint
> +
> +        additionalProperties: false
> +
> +    additionalProperties: false
> +
>  required:
>    - compatible
>    - reg

-- 
Regards,

Sakari Ailus