linux-kernel - Re: [PATCH 25/35] media: venus: Use the correct div

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Message-ID: <06113ffe-11bd-4c73-aff7-5e55aa8e3edc@moroto.mountain>
Date: Wed, 17 Apr 2024 11:36:23 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Martin Tuma <martin.tuma@...iteqautomotive.com>,
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Subject: Re: [PATCH 25/35] media: venus: Use the correct div_ function

On Mon, Apr 15, 2024 at 07:34:42PM +0000, Ricardo Ribalda wrote:
> us_per_frame does not fit in u32
> 

drivers/media/platform/qcom/venus/venc.c
   391  static int venc_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
   392  {
   393          struct venus_inst *inst = to_inst(file);
   394          struct v4l2_outputparm *out = &a->parm.output;
   395          struct v4l2_fract *timeperframe = &out->timeperframe;
   396          u64 us_per_frame, fps;
   397  
   398          if (a->type != V4L2_BUF_TYPE_VIDEO_OUTPUT &&
   399              a->type != V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE)
   400                  return -EINVAL;
   401  
   402          memset(out->reserved, 0, sizeof(out->reserved));
   403  
   404          if (!timeperframe->denominator)
   405                  timeperframe->denominator = inst->timeperframe.denominator;
   406          if (!timeperframe->numerator)
   407                  timeperframe->numerator = inst->timeperframe.numerator;
   408  
   409          out->capability = V4L2_CAP_TIMEPERFRAME;
   410  
   411          us_per_frame = timeperframe->numerator * (u64)USEC_PER_SEC;
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
It looks like in some drivers this multiply can go over U32_MAX.

   412          do_div(us_per_frame, timeperframe->denominator);
                       ^^^^^^^^^^^^
But after this divide, then we're under 1,000,000 again.  Otherwise the
FPS is zero.  So maybe the right thing to do is:

	inst->fps = USEC_PER_SEC / (u32)us_per_frame;

   413  
   414          if (!us_per_frame)
   415                  return -EINVAL;
   416  
   417          fps = (u64)USEC_PER_SEC;
   418          do_div(fps, us_per_frame);
   419  
   420          inst->timeperframe = *timeperframe;
   421          inst->fps = fps;
   422  
   423          return 0;
   424  }

regards,
dan carpenter