linux-kernel - Re: [PATCH v4 1/4] dt-bindings: media: imx258: add bindings for IMX258 sensor

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Message-ID: <20200929110255.GJ26842@paasikivi.fi.intel.com>
Date:   Tue, 29 Sep 2020 14:02:55 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/4] dt-bindings: media: imx258: add bindings for
 IMX258 sensor

On Tue, Sep 29, 2020 at 11:46:36AM +0200, Krzysztof Kozlowski wrote:
> On Tue, Sep 29, 2020 at 12:40:46PM +0300, Sakari Ailus wrote:
> > On Tue, Sep 29, 2020 at 11:18:46AM +0200, Krzysztof Kozlowski wrote:
> > > On Tue, 29 Sep 2020 at 11:15, Sakari Ailus <sakari.ailus@...ux.intel.com> wrote:
> > > >
> > > > Hi Krzysztof,
> > > >
> > > > On Wed, Sep 23, 2020 at 05:21:26PM +0200, Krzysztof Kozlowski wrote:
> > > > > Add bindings for the IMX258 camera sensor.  The bindings, just like the
> > > > > driver, are quite limited, e.g. do not support regulator supplies.
> > > > >
> > > > > Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> > > > >
> > > > > ---
> > > > >
> > > > > Changes since v3:
> > > > > 1. Document also two lane setup.
> > > > >
> > > > > Changes since v2:
> > > > > 1. Remove clock-frequency, add reset GPIOs, add supplies.
> > > >
> > > > Oops. I missed this one.
> > > >
> > > > How does the driver know the appropriate clock frequency for the platform
> > > > if it's not in DT? The sensor supports a range of frequencies, not a single
> > > > frequency.
> > > >
> > > > Could you add clock-frequency back?
> > > 
> > > Not really, it was removed on Rob's request. The bindings do not
> > > describe driver's behavior so how the driver gets frequency should not
> > > be part of the bindings. Also it's not a real problem - the driver
> > > just calls clk_get_rate().
> > 
> > How is the rate determined? I mean, many ISPs or CSI-2 receivers that
> > provide the clock are also capable of using a variety of frequencies. But
> > only one can be used on the platform in general.
> 
> Having "clock-frequency" property in DTS did not solve that. It has no
> effect on actual frequency.

It's up to the driver to do what's needed, yes.

Please see examples in e.g. drivers/media/i2c/ov8856.c and
Documentation/devicetree/bindings/media/i2c/ov8856.yaml .

-- 
Sakari Ailus