Re: [PATCH v3 23/26] media: venus: vdec: Make the range of us_per_frame explicit

[Hans Verkuil <hverkuil@xs4all.nl>]

On 29/04/2024 17:05, Ricardo Ribalda wrote:
> Unless the fps is smaller than 0.000232829 fps, this fits in a 32 bit
> number. Make that explicit.
> 
> Found by cocci:
> drivers/media/platform/qcom/venus/vdec.c:488:1-7: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
> 
> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  drivers/media/platform/qcom/venus/vdec.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c
> index 29130a9441e7..2b2874aedb2d 100644
> --- a/drivers/media/platform/qcom/venus/vdec.c
> +++ b/drivers/media/platform/qcom/venus/vdec.c
> @@ -464,7 +464,7 @@ static int vdec_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
>  	struct venus_inst *inst = to_inst(file);
>  	struct v4l2_captureparm *cap = &a->parm.capture;
>  	struct v4l2_fract *timeperframe = &cap->timeperframe;
> -	u64 us_per_frame, fps;
> +	u64 us_per_frame;
>  
>  	if (a->type != V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE &&
>  	    a->type != V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE)
> @@ -484,10 +484,7 @@ static int vdec_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
>  	if (!us_per_frame)
>  		return -EINVAL;
>  
> -	fps = (u64)USEC_PER_SEC;
> -	do_div(fps, us_per_frame);
> -
> -	inst->fps = fps;
> +	inst->fps = USEC_PER_SEC / (u32)us_per_frame;

What happens if us_per_frame > USEC_PER_SEC? inst->fps is now 0, and I wonder what
issues that may cause.

I will drop this patch from the PR, as it is probably wise to return an error if
us_per_frame > USEC_PER_SEC.

The same issue is present with the venc patch (24/26), but that wasn't included in
the PR anyway.

Regards,

	Hans

>  	inst->timeperframe = *timeperframe;
>  
>  	return 0;
>