linux-kernel - Re: [PATCH v11 06/15] drm/vkms: Avoid computing blending limits inside pre_mul_alpha

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Message-ID: <30573f5a-d3dd-4aa4-ac5a-cf6df77b79dc@infradead.org>
Date: Tue, 1 Oct 2024 20:54:41 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Louis Chauvet <louis.chauvet@...tlin.com>,
 Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
 Melissa Wen <melissa.srw@...il.com>, Maíra Canal
 <mairacanal@...eup.net>, Haneen Mohammed <hamohammed.sa@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Jonathan Corbet <corbet@....net>,
 Simona Vetter <simona@...ll.ch>, arthurgrillo@...eup.net,
 pekka.paalanen@...oniitty.fi, Simona Vetter <simona.vetter@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, thomas.petazzoni@...tlin.com,
 jeremie.dautheribes@...tlin.com, miquel.raynal@...tlin.com,
 seanpaul@...gle.com, marcheu@...gle.com, nicolejadeyee@...gle.com,
 Pekka Paalanen <pekka.paalanen@...labora.com>
Subject: Re: [PATCH v11 06/15] drm/vkms: Avoid computing blending limits
 inside pre_mul_alpha_blend

Hi--

On 9/30/24 8:31 AM, Louis Chauvet wrote:
> The pre_mul_alpha_blend is dedicated to blending, so to avoid mixing
> different concepts (coordinate calculation and color management), extract
> the x_limit and x_dst computation outside of this helper.
> It also increases the maintainability by grouping the computation related
> to coordinates in the same place: the loop in `blend`.
> 
> Reviewed-by: Pekka Paalanen <pekka.paalanen@...labora.com>
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> ---
>  drivers/gpu/drm/vkms/vkms_composer.c | 40 +++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index 931e214b225c..4d220bbb023c 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -24,34 +24,30 @@ static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)
>  
>  /**
>   * pre_mul_alpha_blend - alpha blending equation
> - * @frame_info: Source framebuffer's metadata
>   * @stage_buffer: The line with the pixels from src_plane
>   * @output_buffer: A line buffer that receives all the blends output
> + * @x_start: The start offset
> + * @pixel_count: The number of pixels to blend

so is this actually pixel count + 1; or

>   *
> - * Using the information from the `frame_info`, this blends only the
> - * necessary pixels from the `stage_buffer` to the `output_buffer`
> - * using premultiplied blend formula.
> + * The pixels 0..@...el_count in stage_buffer are blended at @x_start..@...tart+@...el_count in

should these ranges include a "- 1"?
Else please explain.

> + * output_buffer.