Re: [PATCH 1/7] drm: Fix drm_fixp2int_round() making it add 0.5

[Melissa Wen]

On 03/06, Arthur Grillo wrote:
> As well noted by Pekka[1], the rounding of drm_fixp2int_round is wrong.
> To round a number, you need to add 0.5 to the number and floor that,
> drm_fixp2int_round() is adding 0.0000076. Make it add 0.5.
> 
> [1]: https://lore.kernel.org/all/20240301135327.22efe0dd.pekka.paalanen@xxxxxxxxxxxxx/
> 
Hi Arthur,

thanks for addressing this issue.

Please, add a fix tag to the commit that you are fixing, so we can
easily backport. Might be this commit:
https://cgit.freedesktop.org/drm/drm-misc/commit/drivers/gpu/drm/vkms?id=ab87f558dcfb2562c3497e89600dec798a446665
> Suggested-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
> Signed-off-by: Arthur Grillo <arthurgrillo@xxxxxxxxxx>
> ---
>  include/drm/drm_fixed.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
> index 0c9f917a4d4b..de3a79909ac9 100644
> --- a/include/drm/drm_fixed.h
> +++ b/include/drm/drm_fixed.h
> @@ -90,7 +90,7 @@ static inline int drm_fixp2int(s64 a)
>  
>  static inline int drm_fixp2int_round(s64 a)
>  {
> -	return drm_fixp2int(a + (1 << (DRM_FIXED_POINT_HALF - 1)));
Also, this is the only usage of DRM_FIXED_POINT_HALF. Can you also
remove it as it won't be used anymore?

> +	return drm_fixp2int(a + DRM_FIXED_ONE / 2);
Would this division be equivalent to just shifting 1ULL by 31 instead of
32 as done in DRM_FIXED_ONE?

Melissa

>  }
>  
>  static inline int drm_fixp2int_ceil(s64 a)
> 
> -- 
> 2.43.0
>