linux-kernel - Re: [PATCH v2 1/3] dt-bindings: media: i2c: Add IMX290 CMOS sensor binding

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Message-ID: <20190813115204.GB2527@valkosipuli.retiisi.org.uk>
Date:   Tue, 13 Aug 2019 14:52:04 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        mchehab@...nel.org, robh+dt@...nel.org, devicetree@...r.kernel.org,
        c.barrett@...mos.com, linux-kernel@...r.kernel.org,
        a.brela@...mos.com, linux-arm-kernel@...ts.infradead.org,
        linux-media@...r.kernel.org
Subject: Re: [PATCH v2 1/3] dt-bindings: media: i2c: Add IMX290 CMOS sensor
 binding

Hi Russell,

On Tue, Aug 13, 2019 at 12:38:46PM +0100, Russell King - ARM Linux admin wrote:
> On Tue, Aug 06, 2019 at 06:39:36PM +0530, Manivannan Sadhasivam wrote:
> > +Required Properties:
> > +- compatible: Should be "sony,imx290"
> > +- reg: I2C bus address of the device
> > +- clocks: Reference to the xclk clock.
> > +- clock-names: Should be "xclk".
> > +- clock-frequency: Frequency of the xclk clock.
> 
> Driver code:
> 
> +       ret = of_property_read_u32(dev->of_node, "clock-frequency", &xclk_freq);+       if (ret) {
> +               dev_err(dev, "Could not get xclk frequency\n");
> +               return ret;
> +       }
> +
> +       /* external clock must be 37.125 MHz */
> +       if (xclk_freq != 37125000) {
> +               dev_err(dev, "External clock frequency %u is not supported\n",
> +                       xclk_freq);
> +               return -EINVAL;
> +       }
> 
> So, only 37125000 is supported - is that not worth mentioning in this
> description?  Is this a hard requirement of the sensor?  If so, why
> does it need to be mentioned in the DT binding?

The driver only supports a particular frequency, but the sensor is not
limited to that. Unfortunately this is not uncommon for camera sensors, for
the vendors often provide register settings for a given configuration only
(external clock frequency, number of CSI-2 lanes, CSI-2 bus frequency,
image cropping, binning etc.).

That still doesn't mean there are no alternative configurations for
different external clock frequencies, or that there could not be a driver
that was able to configure the sensor to use a given frequency.

-- 
Regards,

Sakari Ailus