linux-kernel - Re: [PATCH v2 6/6] media: imx335: Limit analogue gain value

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Date: Fri, 8 Mar 2024 12:25:05 +0100
From: Tommaso Merciai <tomm.merciai@...il.com>
To: Umang Jain <umang.jain@...asonboard.com>
Cc: linux-media@...r.kernel.org,
	Alexander Shiyan <eagle.alexander923@...il.com>,
	Kieran Bingham <kieran.bingham@...asonboard.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	open list <linux-kernel@...r.kernel.org>,
	Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: Re: [PATCH v2 6/6] media: imx335: Limit analogue gain value

Hi Umang,

On Fri, Mar 08, 2024 at 02:03:12PM +0530, Umang Jain wrote:
> The sensor gain (both analog and digital) are controlled by a
> single gain value where:
> - 0dB to 30dB correspond to analog gain
> - 30.3dB to 72dB correspond to digital gain
>   (with 0.3dB step)
> 
> Hence, limit the analogue gain value to 100.
> For digital gain, support can be added later if needed.
> 
> Signed-off-by: Umang Jain <umang.jain@...asonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham@...asonboard.com>
> ---
>  drivers/media/i2c/imx335.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/imx335.c b/drivers/media/i2c/imx335.c
> index 85cb53e3d5d4..cc59f446cd09 100644
> --- a/drivers/media/i2c/imx335.c
> +++ b/drivers/media/i2c/imx335.c
> @@ -53,7 +53,7 @@
>  /* Analog gain control */
>  #define IMX335_REG_AGAIN		CCI_REG8(0x30e8)
>  #define IMX335_AGAIN_MIN		0
> -#define IMX335_AGAIN_MAX		240
> +#define IMX335_AGAIN_MAX		100
>  #define IMX335_AGAIN_STEP		1
>  #define IMX335_AGAIN_DEFAULT		0
>  
> @@ -1174,6 +1174,14 @@ static int imx335_init_controls(struct imx335 *imx335)
>  					     IMX335_EXPOSURE_STEP,
>  					     IMX335_EXPOSURE_DEFAULT);
>  
> +	/*
> +	 * The sensor has an analog gain and a digital gain, both controlled
> +	 * through a single gain value, expressed in 0.3dB increments. Values
> +	 * from 0.0dB (0) to 30.0dB (100) apply analog gain only, higher values
> +	 * up to 72.0dB (240) add further digital gain. Limit the range to
> +	 * analog gain only, support for digital gain can be added separately
> +	 * if needed.
> +	 */
>  	imx335->again_ctrl = v4l2_ctrl_new_std(ctrl_hdlr,
>  					       &imx335_ctrl_ops,
>  					       V4L2_CID_ANALOGUE_GAIN,
> -- 
> 2.43.0
> 
> 

Unfortunately I don't have the datasheet of this sensor but the logic
behind this patch looks good to me. :)

Btw I check the datasheet of IMX323LQN-C and the gain controll logic
it's pretty similar except for the values in dB (different sensor).
Hope this help.

Reviewed-by: Tommaso Merciai <tomm.merciai@...il.com>

Thanks & Regards,
Tommaso