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

[Nick Desaulniers]

On Tue, Jul 18, 2023 at 2:44 PM Nathan Chancellor <nathan at kernel.org> 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 at kernel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers at google.com>

> ---
>  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;
>
>
> --
> 2.41.0
>


-- 
Thanks,
~Nick Desaulniers