Re: [PATCH v2 2/6] media: i2c: mt9p031: Rewrite a bitwise mask

[Laurent Pinchart]

On Fri, May 01, 2026 at 11:32:47AM +0000, Ricardo Ribalda wrote:
> The current code makes smatch a bit uncomfortable:
> drivers/media/i2c/mt9p031.c:799 mt9p031_s_ctrl() warn: assigning (-1952) to unsigned variable 'data'
> 
> Probably because smatch is not clever enough (yet). Do a simple rewrite
> to make sure that smatch understands what we are doing here.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
>  drivers/media/i2c/mt9p031.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
> index ea5d43d925ff..5c9dff030b4d 100644
> --- a/drivers/media/i2c/mt9p031.c
> +++ b/drivers/media/i2c/mt9p031.c
> @@ -795,7 +795,7 @@ static int mt9p031_s_ctrl(struct v4l2_ctrl *ctrl)
>  			ctrl->val &= ~1;
>  			data = (1 << 6) | (ctrl->val >> 1);
>  		} else {
> -			ctrl->val &= ~7;
> +			ctrl->val -= ctrl->val % 8;
>  			data = ((ctrl->val - 64) << 5) | (1 << 6) | 32;

I'd still like to keep the ~7 (and, while at it, making the register
computation easier to read). I previously proposed

			ctrl->val &= ~7;
			data = (ctrl->val - 64) >> 3;
			data = (data << 8) | (1 << 6) | 32;

which didn't quite appease smatch. We could use an explicit mask:

			ctrl->val &= ~7;
			data = ((ctrl->val - 64) >> 3) & 0xff;
			data = (data << 8) | (1 << 6) | 32;

>  		}
>  
> 

-- 
Regards,

Laurent Pinchart