linux-kernel - Re: [PATCH v2 1/3] dt-bindings: media: ov772x: Document endpoint properties

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Message-ID: <20200806143559.ha6amfa4gq2o4jbi@uno.localdomain>
Date:   Thu, 6 Aug 2020 16:35:59 +0200
From:   Jacopo Mondi <jacopo@...ndi.org>
To:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Prabhakar <prabhakar.csengg@...il.com>,
        linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2 1/3] dt-bindings: media: ov772x: Document endpoint
 properties

Hi Prabhakar,

On Mon, Aug 03, 2020 at 12:39:11PM +0100, Lad Prabhakar wrote:
> Document endpoint properties required for parallel interface
>
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> ---
>  .../devicetree/bindings/media/i2c/ov772x.txt     | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/media/i2c/ov772x.txt b/Documentation/devicetree/bindings/media/i2c/ov772x.txt
> index 0b3ede5b8e6a..1f4153484717 100644
> --- a/Documentation/devicetree/bindings/media/i2c/ov772x.txt
> +++ b/Documentation/devicetree/bindings/media/i2c/ov772x.txt
> @@ -21,6 +21,22 @@ subnode for its digital output video port, in accordance with the video
>  interface bindings defined in Documentation/devicetree/bindings/media/
>  video-interfaces.txt.
>
> +Endpoint node required properties for parallel connection are:
> +- remote-endpoint: a phandle to the bus receiver's endpoint node.

we allow endpoints without a remote end connected usually. They can be
filled in later, in example, with an overlay.

> +- bus-width: shall be set to <8> for 8 bits parallel bus
> +	     or <10> for 10 bits parallel bus
> +- data-shift: shall be set to <2> for 8 bits parallel bus
> +	      (lines 9:2 are used) or <0> for 10 bits parallel bus

defining what is required or optional might be hard. I don't see the
driver enforcing their presence and I assume they have safe default.
Maybe make them optional and specify what the defaul value is ?


> +- hsync-active: active state of the HSYNC signal, 0/1 for LOW/HIGH respectively.
> +		(Not required for bus-type equal 6)
> +- vsync-active: active state of the VSYNC signal, 0/1 for LOW/HIGH respectively.
> +		(Not required for bus-type equal 6)

If they're not required, they're optional, aren't they ? :)

> +- pclk-sample: sample data on rising (1) or falling (0) edge of the pixel clock
> +	       signal. (Not required for bus-type equal 6)

Why the pclk polarity is does not apply to BT.656 ?

> +- bus-type: data bus type. Possible values are:
> +	    5 - Parallel
> +	    6 - Bt.656

Are we making this required, or do we expect this to be deduced
depending on which other properties have been specified ? Sakari it
seems you would like this to become a properties that has to be
specified most of the times, right ? (I tend to agree with that FWIW),
but does it impact retro-compatibility ?

> +
>  Example:
>
>  &i2c0 {
> --
> 2.17.1
>