linux-kernel - Re: [PATCH v2] drm: Fix drm_fixp2int

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Date: Sun, 17 Mar 2024 14:50:42 -0300
From: Melissa Wen <mwen@...lia.com>
To: Arthur Grillo <arthurgrillo@...eup.net>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Maíra Canal <mcanal@...lia.com>, Pekka Paalanen <pekka.paalanen@...labora.com>, 
	Harry Wentland <harry.wentland@....com>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm: Fix drm_fixp2int_round() making it add 0.5

On 03/16, 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@collabora.com/
> 
> Fixes: 8b25320887d7 ("drm: Add fixed-point helper to get rounded integer values")
> Suggested-by: Pekka Paalanen <pekka.paalanen@...labora.com>
> Reviewed-by: Harry Wentland <harry.wentland@....com>
> Signed-off-by: Arthur Grillo <arthurgrillo@...eup.net>

Great, thanks!

Reviewed-by: Melissa Wen <mwen@...lia.com>

I'll apply to drm-misc-next.

Melissa

> ---
> Changes in v2:
> - Add Fixes tag (Melissa Wen)
> - Remove DRM_FIXED_POINT_HALF (Melissa Wen)
> - Link to v1: https://lore.kernel.org/all/20240306-louis-vkms-conv-v1-1-5bfe7d129fdd@riseup.net/
> ---
>  include/drm/drm_fixed.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
> index 0c9f917a4d4b..81572d32db0c 100644
> --- a/include/drm/drm_fixed.h
> +++ b/include/drm/drm_fixed.h
> @@ -71,7 +71,6 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
>  }
>  
>  #define DRM_FIXED_POINT		32
> -#define DRM_FIXED_POINT_HALF	16
>  #define DRM_FIXED_ONE		(1ULL << DRM_FIXED_POINT)
>  #define DRM_FIXED_DECIMAL_MASK	(DRM_FIXED_ONE - 1)
>  #define DRM_FIXED_DIGITS_MASK	(~DRM_FIXED_DECIMAL_MASK)
> @@ -90,7 +89,7 @@ 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)));
> +	return drm_fixp2int(a + DRM_FIXED_ONE / 2);
>  }
>  
>  static inline int drm_fixp2int_ceil(s64 a)
> 
> ---
> base-commit: f89632a9e5fa6c4787c14458cd42a9ef42025434
> change-id: 20240315-drm_fixed-c680ba078ecb
> 
> Best regards,
> -- 
> Arthur Grillo <arthurgrillo@...eup.net>
>