Re: [Intel-gfx] [PATCH 1/2] drm/v3d: Avoid -Wconstant-logical-operand in nsecs_to_jiffies_timeout()

[Nathan Chancellor <nathan@kernel.org>]

Hi Maira,

On Thu, Jul 27, 2023 at 11:01:27AM -0300, Maira Canal wrote:
> Hi Nathan,
> 
> On 7/18/23 18:44, Nathan Chancellor wrote:
> > A proposed update to clang's -Wconstant-logical-operand to warn when the
> > left hand side is a constant shows the following instance in
> > nsecs_to_jiffies_timeout() when NSEC_PER_SEC is not a multiple of HZ,
> > such as CONFIG_HZ=300:
> > 
> >    In file included from drivers/gpu/drm/v3d/v3d_debugfs.c:12:
> >    drivers/gpu/drm/v3d/v3d_drv.h:343:24: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand]
> >      343 |         if (NSEC_PER_SEC % HZ &&
> >          |             ~~~~~~~~~~~~~~~~~ ^
> >    drivers/gpu/drm/v3d/v3d_drv.h:343:24: note: use '&' for a bitwise operation
> >      343 |         if (NSEC_PER_SEC % HZ &&
> >          |                               ^~
> >          |                               &
> >    drivers/gpu/drm/v3d/v3d_drv.h:343:24: note: remove constant to silence this warning
> >    1 warning generated.
> > 
> > Turn this into an explicit comparison against zero to make the
> > expression a boolean to make it clear this should be a logical check,
> > not a bitwise one.
> > 
> > Link: https://reviews.llvm.org/D142609
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> 
> Reviewed-by: Maíra Canal <mcanal@igalia.com>
> 
> Thanks for all the hard work with clang! Let me know if you need someone
> to push it to drm-misc-next.

Yes I will, I do not have drm commit rights. I think the i915 patch can
go to drm-misc as well with Tvrtko's ack. Thanks a lot for taking a
look!

Cheers,
Nathan

> Best Regards,
> - Maíra
> 
> > ---
> >   drivers/gpu/drm/v3d/v3d_drv.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
> > index b74b1351bfc8..7f664a4b2a75 100644
> > --- a/drivers/gpu/drm/v3d/v3d_drv.h
> > +++ b/drivers/gpu/drm/v3d/v3d_drv.h
> > @@ -340,7 +340,7 @@ struct v3d_submit_ext {
> >   static inline unsigned long nsecs_to_jiffies_timeout(const u64 n)
> >   {
> >   	/* nsecs_to_jiffies64() does not guard against overflow */
> > -	if (NSEC_PER_SEC % HZ &&
> > +	if ((NSEC_PER_SEC % HZ) != 0 &&
> >   	    div_u64(n, NSEC_PER_SEC) >= MAX_JIFFY_OFFSET / HZ)
> >   		return MAX_JIFFY_OFFSET;
> >