linux-kernel - Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module

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Date:   Fri, 23 Jun 2017 12:59:24 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Andreas Färber <afaerber@...e.de>,
        Suman Anna <s-anna@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Hugues Fruchet <hugues.fruchet@...com>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Alexandre Torgue <alexandre.torgue@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Yannick Fertre <yannick.fertre@...com>,
        Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Guennadi Liakhovetski <g.liakhovetski@....de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-media@...r.kernel.org
Subject: Re: [PATCH v1 1/6] DT bindings: add bindings for ov965x camera module


> Am 23.06.2017 um 12:46 schrieb Andreas Färber <afaerber@...e.de>:
> 
> Hi,
> 
> Am 23.06.2017 um 12:25 schrieb H. Nikolaus Schaller:
>>> diff --git a/Documentation/devicetree/bindings/media/i2c/ov965x.txt b/Documentation/devicetree/bindings/media/i2c/ov965x.txt
>>> new file mode 100644
>>> index 0000000..0e0de1f
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/media/i2c/ov965x.txt
>>> @@ -0,0 +1,37 @@
>>> +* Omnivision OV9650/9652/9655 CMOS sensor
>>> +
>>> +The Omnivision OV965x sensor support multiple resolutions output, such as
>>> +CIF, SVGA, UXGA. It also can support YUV422/420, RGB565/555 or raw RGB
>>> +output format.
>>> +
>>> +Required Properties:
>>> +- compatible: should be one of
>>> +	"ovti,ov9650"
>>> +	"ovti,ov9652"
>>> +	"ovti,ov9655"
>>> +- clocks: reference to the mclk input clock.
>> 
>> I wonder why you have removed the clock-frequency property?
>> 
>> In some situations the camera driver must be able to tell the clock source
>> which frequency it wants to see.
> 
> That's what assigned-clock-rates property is for:
> 
> https://www.kernel.org/doc/Documentation/devicetree/bindings/clock/clock-bindings.txt
> 
> AFAIU clock-frequency on devices is deprecated and equivalent to having
> a clocks property pointing to a fixed-clock, which is different from a
> clock with varying rate.

I am not sure if that helps here. The OMAP3-ISP does not have a fixed clock rate
so we can only have the driver define what it wants to see.

And common practise for OMAP3-ISP based camera modules (e.g. N900, N9) is that they do it in the driver.

Maybe ISP developers can comment?

BR,
Nikolaus