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

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Message-ID: <e209912c-7a5c-b219-5b38-9b0b722be936@ti.com>
Date:   Fri, 23 Jun 2017 17:24:26 -0500
From:   Suman Anna <s-anna@...com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>,
        Andreas Färber <afaerber@...e.de>,
        Hugues Fruchet <hugues.fruchet@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     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

On 06/23/2017 01:59 PM, H. Nikolaus Schaller wrote:
> Hi Suman,
> 
>> Am 23.06.2017 um 20:05 schrieb Suman Anna <s-anna@...com>:
>>
>>>>>
>>>>> Or does it just mean that it defines the property name?
>>>>
>>>> Please read the documentation link I sent - it's in the very bottom and
>>>> should have an example.
>>>
>>> I have seen it but it does not give me a good clue how to translate that into
>>> correct omap3isp node setup in a specific DT. Rather it raises more questions.
>>> Maybe because I don't understand completely what it is talking about.
>>>
>>> The fundamental question is if this "assigned-clock-rates" is already
>>> handled by ov965x->clk = devm_clk_get(&client->dev, NULL); ?
>>>
>>> Or should we define that for the omap3isp node?
>>>
>>> Then of course we need no new code and just use the right property names.
>>> And N900, N9 camera DTs should be updated.
>>
>> Look up of_clk_set_defaults() function in drivers/clk/clk-conf.c. This
>> function gets invoked usually during clock registration, and also gets
>> called in platform_drv_probe(), so the parents and clocks do get
>> configured before your driver gets probed. So, this provides a default
>> configuration if these properties are supplied (in either clock nodes or
>> actual device nodes), and if your driver needs to change the rates at
>> runtime, then you would have to do that in the driver itself.
> 
> Ok, now I understand. Thanks!
> 
> Quite hidden, but nice feature. I would never have thought that it exists.
> Especially as there are no examples around omap3isp cameras...
> 
> And an fgrep assigned-clock-rates shows not many use cases outside CPU/SoC
> include files.
> 
> But interestingly arch/arm/boot/dts/at91sam9g25ek.dts uses it for an ovti,ov2640 camera...
> 
> So it seems that we just have to write:
> 
> 	ov9655@30 {
> 		compatible = "ovti,ov9655";
> 		reg = <0x30>;
> 		clocks = <&isp 0>;	/* cam_clka */
> 		assigned-clocks = <&isp 0>;
> 		assigned-clock-rates = <24000000>;
> 	};

Yeah, that looks alright and should work.

regards
Suman

> 
> instead of introducing a new clock-frequency property and code to handle it.
> 
> Or do I misinterpret what "parents" and "clocks" are in this context?