linux-kernel - Re: [PATCH v3 19/23] media: atmel: atmel-isc-base: clamp wb gain coefficients

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Date:   Wed, 12 Jan 2022 10:04:05 +0100
From:   Jacopo Mondi <jacopo@...ndi.org>
To:     Eugen Hristev <eugen.hristev@...rochip.com>
Cc:     linux-media@...r.kernel.org, robh+dt@...nel.org,
        laurent.pinchart@...asonboard.com, sakari.ailus@....fi,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, nicolas.ferre@...rochip.com
Subject: Re: [PATCH v3 19/23] media: atmel: atmel-isc-base: clamp wb gain
 coefficients

Hi Eugen

On Mon, Dec 13, 2021 at 03:49:36PM +0200, Eugen Hristev wrote:
> White balance computed gains can overflow above the 13 bits hardware
> coefficient that can be used, in some specific scenarios like a subexposure
> from the sensor when the image is mostly black.
> In this case the computed gain has to be clamped to the maximum value
> allowed by the hardware.
>
> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
> ---
>  drivers/media/platform/atmel/atmel-isc-base.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/media/platform/atmel/atmel-isc-base.c b/drivers/media/platform/atmel/atmel-isc-base.c
> index f1f1019f9d82..31c8e3029eee 100644
> --- a/drivers/media/platform/atmel/atmel-isc-base.c
> +++ b/drivers/media/platform/atmel/atmel-isc-base.c
> @@ -1415,6 +1415,10 @@ static void isc_wb_update(struct isc_ctrls *ctrls)
>  		/* multiply both gains and adjust for decimals */
>  		ctrls->gain[c] = s_gain[c] * gw_gain[c];
>  		ctrls->gain[c] >>= 9;
> +
> +		/* make sure we are not out of range */
> +		ctrls->gain[c] = clamp_val(ctrls->gain[c], 0, GENMASK(12, 0));

#include <linux/minmax.h>

What is the type of gain[c} ? If it's unsigned clamping with [0 is not
required. I would in that case gain[c] = min(gain[c], ...)

It's fine anyway
Reviewed-by: Jacopo Mondi <jacopo+renesas@...ndi.org>

Thanks
   j


> +
>  		v4l2_dbg(1, debug, &isc->v4l2_dev,
>  			 "isc wb: component %d, final gain %u\n",
>  			 c, ctrls->gain[c]);
> --
> 2.25.1
>