Re: [PATCH] [media] mt9v032: do not clear reserved bits in read mode register

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Philipp,

Thank you for the patch.

On Monday 26 May 2014 15:59:35 Philipp Zabel wrote:
> The read mode register bits 8 and 9 are set and marked as reserved.
> Don't clear them.

Good catch. Have you noticed any issue in practice ?

> Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> ---
>  drivers/media/i2c/mt9v032.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/i2c/mt9v032.c b/drivers/media/i2c/mt9v032.c
> index 33a110a..052e754 100644
> --- a/drivers/media/i2c/mt9v032.c
> +++ b/drivers/media/i2c/mt9v032.c
> @@ -415,6 +415,7 @@ static int mt9v032_s_stream(struct v4l2_subdev *subdev,
> int enable) struct i2c_client *client = v4l2_get_subdevdata(subdev);
>  	struct mt9v032 *mt9v032 = to_mt9v032(subdev);
>  	struct v4l2_rect *crop = &mt9v032->crop;
> +	unsigned int read_mode;
>  	unsigned int hbin;
>  	unsigned int vbin;
>  	int ret;
> @@ -425,9 +426,11 @@ static int mt9v032_s_stream(struct v4l2_subdev *subdev,
> int enable) /* Configure the window size and row/column bin */
>  	hbin = fls(mt9v032->hratio) - 1;
>  	vbin = fls(mt9v032->vratio) - 1;
> -	ret = mt9v032_write(client, MT9V032_READ_MODE,
> -			    hbin << MT9V032_READ_MODE_COLUMN_BIN_SHIFT |
> -			    vbin << MT9V032_READ_MODE_ROW_BIN_SHIFT);
> +	read_mode = mt9v032_read(client, MT9V032_READ_MODE);

Shouldn't you check the return value for errors here ?

> +	read_mode &= ~0xff; /* bits 0x300 are reserved */

What about defining an MT9V032_READ_MODE_RESERVED macro set to 0x0300 and 
using it here ?

> +	read_mode |= hbin << MT9V032_READ_MODE_COLUMN_BIN_SHIFT |
> +		     vbin << MT9V032_READ_MODE_ROW_BIN_SHIFT;
> +	ret = mt9v032_write(client, MT9V032_READ_MODE, read_mode);

I'm tempted to create an mt9v032_write_read_mode function, as the code is 
getting a bit complex:

static int mt9v032_write_read_mode(struct mt9v032 *mt9v032, u16 value)
{
	struct i2c_client *client = v4l2_get_subdevdata(&mt9v032->subdev);
	int ret;

	ret = mt9v032_read(client, MT9V032_READ_MODE);
	if (ret < 0)
		return ret;

	ret &= ~MT9V032_READ_MODE_RESERVED;
	ret |= value;

	return mt9v032_write(client, MT9V032_READ_MODE, ret);
}

But I'll leave that up to you, feel free to ignore the suggestion.

>  	if (ret < 0)
>  		return ret;

-- 
Regards,

Laurent Pinchart