linux-kernel - Re: [PATCH v4 3/5] media: i2c: ov5645: Increase tolerance of external clock frequency

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Date:   Thu, 19 Mar 2020 16:50:12 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        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>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Lad Prabhakar <prabhakar.csengg@...il.com>
Subject: Re: [PATCH v4 3/5] media: i2c: ov5645: Increase tolerance of
 external clock frequency

Hi Prabhakar,

Thank you for the patch.

On Thu, Mar 19, 2020 at 12:19:21PM +0000, Lad Prabhakar wrote:
> While testing on Renesas RZ/G2E platform, noticed the clock frequency to
> be 24242424 as a result the probe failed.
> 
> This patch increases the tolerance to 5% so that it avoids patching for
> new platforms and it warns the users if the frequency is not within the
> range and continue further in the probe instead of returning failure.
> 
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> ---
>  drivers/media/i2c/ov5645.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov5645.c b/drivers/media/i2c/ov5645.c
> index e298acdadeef..52a185ed4368 100644
> --- a/drivers/media/i2c/ov5645.c
> +++ b/drivers/media/i2c/ov5645.c
> @@ -1105,13 +1105,11 @@ static int ov5645_probe(struct i2c_client *client)
>  		}
>  	}
>  
> -	/* external clock must be 24MHz, allow 1% tolerance */
> +	/* ideally external clock must be 24MHz, allow 5% tolerance */
>  	xclk_freq = clk_get_rate(ov5645->xclk);
> -	if (xclk_freq < 23760000 || xclk_freq > 24240000) {
> -		dev_err(dev, "external clock frequency %u is not supported\n",
> -			xclk_freq);
> -		return -EINVAL;
> -	}
> +	if (xclk_freq < 22800000 || xclk_freq > 25200000)
> +		dev_warn(dev, "external clock frequency is set to %u, sensor might misbehave\n",
> +			 xclk_freq);

The code looks good to me. You may want to mention in the commit subject
that the probe error is turned into a warning, but that may be hard to
do on a single line. Splitting this in two patches could be best, but is
not worth a new version if it's the only change required. If more
changes are required, you can consider it.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

>  	for (i = 0; i < OV5645_NUM_SUPPLIES; i++)
>  		ov5645->supplies[i].supply = ov5645_supply_name[i];

-- 
Regards,

Laurent Pinchart