Re: [PATCH] mt9p031: Really disable Black Level Calibration in test pattern mode

[Hans Verkuil <hansverk@cisco.com>]

Hi Laurent,

The patch is correct, but I noticed a pre-existing bug that should be
fixed. See below.

On 05/07/14 17:40, Laurent Pinchart wrote:
> The digital side of the Black Level Calibration (BLC) function must be
> disabled when generating a test pattern to avoid artifacts in the image.
> The driver disables BLC correctly at the hardware level, but the feature
> gets reenabled by v4l2_ctrl_handler_setup() the next time the device is
> powered on.
> 
> Fix this by marking the BLC controls as inactive when generating a test
> pattern, and ignoring control set requests on inactive controls.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> ---
>  drivers/media/i2c/mt9p031.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
> index 33daace..9102b23 100644
> --- a/drivers/media/i2c/mt9p031.c
> +++ b/drivers/media/i2c/mt9p031.c
> @@ -655,6 +655,9 @@ static int mt9p031_s_ctrl(struct v4l2_ctrl *ctrl)
>  	u16 data;
>  	int ret;
>  
> +	if (ctrl->flags & V4L2_CTRL_FLAG_INACTIVE)
> +		return 0;
> +
>  	switch (ctrl->id) {
>  	case V4L2_CID_EXPOSURE:
>  		ret = mt9p031_write(client, MT9P031_SHUTTER_WIDTH_UPPER,
> @@ -709,8 +712,16 @@ static int mt9p031_s_ctrl(struct v4l2_ctrl *ctrl)
>  					MT9P031_READ_MODE_2_ROW_MIR, 0);
>  
>  	case V4L2_CID_TEST_PATTERN:
> +		/* The digital side of the Black Level Calibration function must
> +		 * be disabled when generating a test pattern to avoid artifacts
> +		 * in the image. Activate (deactivate) the BLC-related controls
> +		 * when the test pattern is enabled (disabled).
> +		 */
> +		v4l2_ctrl_activate(mt9p031->blc_auto, ctrl->val == 0);
> +		v4l2_ctrl_activate(mt9p031->blc_offset, ctrl->val == 0);
> +
>  		if (!ctrl->val) {
> -			/* Restore the black level compensation settings. */
> +			/* Restore the BLC settings. */
>  			if (mt9p031->blc_auto->cur.val != 0) {
>  				ret = mt9p031_s_ctrl(mt9p031->blc_auto);

This doesn't do what you expect. What you want is to set the blc_auto
control to the current value, but mt9p031_s_ctrl(mt9p031->blc_auto) will
set it to the *new* value, which may not be the same. Ditto for doing the
same for blc_offset.

It's best to just call mt9p031_write directly, rather than going through
mt9p031_s_ctrl.

Regards,

	Hans

>  				if (ret < 0)
> @@ -735,9 +746,7 @@ static int mt9p031_s_ctrl(struct v4l2_ctrl *ctrl)
>  		if (ret < 0)
>  			return ret;
>  
> -		/* Disable digital black level compensation when using a test
> -		 * pattern.
> -		 */
> +		/* Disable digital BLC when generating a test pattern. */
>  		ret = mt9p031_set_mode2(mt9p031, MT9P031_READ_MODE_2_ROW_BLC,
>  					0);
>  		if (ret < 0)
>