| Message ID | 1644395913-4091-1-git-send-email-wangqing@vivo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | media: qcom: use div64_u64() instead of do_div() | expand |
On 09/02/2022 11:38, Qing Wang wrote: > From: Wang Qing <wangqing@vivo.com> > > do_div() does a 64-by-32 division. > When the divisor is u64, do_div() truncates it to 32 bits, this means it > can test non-zero and be truncated to zero for division. > > fix do_div.cocci warning: > do_div() does a 64-by-32 division, please consider using div64_u64 instead. NAK The div64_u64 is not equivalent to do_div. It returns the quotient rather than modifying the first arg. Moreover it is unoptimal on 32-bit arches. > > Signed-off-by: Wang Qing <wangqing@vivo.com> > --- > drivers/media/platform/qcom/venus/vdec.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c > index 91da3f5..941a904 > --- a/drivers/media/platform/qcom/venus/vdec.c > +++ b/drivers/media/platform/qcom/venus/vdec.c > @@ -435,7 +435,7 @@ static int vdec_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a) > return -EINVAL; > > fps = (u64)USEC_PER_SEC; > - do_div(fps, us_per_frame); > + div64_u64(fps, us_per_frame); > > inst->fps = fps; > inst->timeperframe = *timeperframe;
From: Dmitry Baryshkov > Sent: 10 February 2022 10:17 > > On 09/02/2022 11:38, Qing Wang wrote: > > From: Wang Qing <wangqing@vivo.com> > > > > do_div() does a 64-by-32 division. > > When the divisor is u64, do_div() truncates it to 32 bits, this means it > > can test non-zero and be truncated to zero for division. > > > > fix do_div.cocci warning: > > do_div() does a 64-by-32 division, please consider using div64_u64 instead. > > > NAK > > The div64_u64 is not equivalent to do_div. It returns the quotient > rather than modifying the first arg. Moreover it is unoptimal on 32-bit > arches. > > > > > Signed-off-by: Wang Qing <wangqing@vivo.com> > > --- > > drivers/media/platform/qcom/venus/vdec.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c > > index 91da3f5..941a904 > > --- a/drivers/media/platform/qcom/venus/vdec.c > > +++ b/drivers/media/platform/qcom/venus/vdec.c > > @@ -435,7 +435,7 @@ static int vdec_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a) > > return -EINVAL; > > > > fps = (u64)USEC_PER_SEC; > > - do_div(fps, us_per_frame); > > + div64_u64(fps, us_per_frame); That one is particularly insane to begin with. Why was it even do_div()? I guess because: fps = USEC_PER_SEC / us_per_frame; caused the compiler to call the 64bit divide function because the 'us_per_frame' is 64bit - even though the code only makes sense if it is small. The correct fix here is probably to change the type of us_per_frame to 32bit or just do: fps = USEC_PER_FRAM / (unsigned int)us_per_frame. Oh, and fps definitely doesn't need to be 64bit either. IMHO all (and I mean ALL) of these patches to change do_div() to div64_u64() need dropping. Maybe one or two are real problems, but the surrounding code needs correctly examining. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c index 91da3f5..941a904 --- a/drivers/media/platform/qcom/venus/vdec.c +++ b/drivers/media/platform/qcom/venus/vdec.c @@ -435,7 +435,7 @@ static int vdec_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a) return -EINVAL; fps = (u64)USEC_PER_SEC; - do_div(fps, us_per_frame); + div64_u64(fps, us_per_frame); inst->fps = fps; inst->timeperframe = *timeperframe;