Re: [PATCH v4 6/6] media: venus: vdec: Make the range of us_per_frame explicit

[Stanimir Varbanov <svarbanov@suse.de>]

On 1/7/25 11:35 AM, Hans Verkuil wrote:
> On 06/01/2025 14:40, Ricardo Ribalda wrote:
>> Fps bigger than 0.000232829 fps, this fits in a 32 bit us_per_frame.
>> There is no need to do a 64 bit division here.
>> Also, the driver only works with whole fps.
>>
>> 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 6b8906ced6bc..88f6b5a3a4fe 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)
>> @@ -486,10 +486,7 @@ static int vdec_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
>>  	if (!us_per_frame || us_per_frame > USEC_PER_SEC)
>>  		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;
> 
> This still allows for an fps value of USEC_PER_SEC if us_per_frame is 1.
> 
> Looking at where inst->fps is used I see:
> 
> drivers/media/platform/qcom/venus/pm_helpers.c: return mbs * inst->fps;
> drivers/media/platform/qcom/venus/venc.c:       frate.framerate = inst->fps * (1 << 16);
> 
> (mbs is at most 512x512)
> 
> So if fps is USEC_PER_SEC those calculations will wrap around.
> 
> What is the real maximum fps that the HW can handle?
> 
> Stan? Bryan? It would be nice if there is a proper sanity check here.

It depends on the resolution but I think we could limit the maximum to
240 FPS per instance.

~Stan