linux-kernel - Re: [PATCH v3 3/9] drm/vkms: write/update the documentation for pixel conversion and pixel write functions

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Date: Tue, 27 Feb 2024 16:02:10 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Arthur Grillo <arthurgrillo@...eup.net>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
	Melissa Wen <melissa.srw@...il.com>,
	Maíra Canal <mairacanal@...eup.net>,
	Haneen Mohammed <hamohammed.sa@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	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>,
	pekka.paalanen@...oniitty.fi, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, jeremie.dautheribes@...tlin.com,
	miquel.raynal@...tlin.com, thomas.petazzoni@...tlin.com,
	seanpaul@...gle.com, marcheu@...gle.com, nicolejadeyee@...gle.com
Subject: Re: [PATCH v3 3/9] drm/vkms: write/update the documentation for
 pixel conversion and pixel write functions

Le 26/02/24 - 10:07, Arthur Grillo a écrit :
> 
> 
> On 26/02/24 05:46, Louis Chauvet wrote:
> > Add some documentation on pixel conversion functions.
> > Update of outdated comments for pixel_write functions.
> > 
> > Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> > ---
> >  drivers/gpu/drm/vkms/vkms_composer.c |  4 +++
> >  drivers/gpu/drm/vkms/vkms_drv.h      | 13 ++++++++
> >  drivers/gpu/drm/vkms/vkms_formats.c  | 58 ++++++++++++++++++++++++++++++------
> >  3 files changed, 66 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> > index c6d9b4a65809..5b341222d239 100644
> > --- a/drivers/gpu/drm/vkms/vkms_composer.c
> > +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> > @@ -189,6 +189,10 @@ static void blend(struct vkms_writeback_job *wb,
> >  
> >  	size_t crtc_y_limit = crtc_state->base.crtc->mode.vdisplay;
> >  
> > +	/*
> > +	 * The planes are composed line-by-line. It is a necessary complexity to avoid poor
> > +	 * blending performance.
> 
> At this moment in the series, you have not yet reintroduced the
> line-by-line algorithm yet. Maybe it's better to add this comment when
> you do.

Is it better with this:

	/*
	 * The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
	 * complexity to avoid poor blending performance.
	 *
	 * The function vkms_compose_row is used to read a line, pixel-by-pixel, into the staging
	 * buffer.
	 */
 
> Also, I think it's good to give more context, like:
> "The planes are composed line-by-line, instead of pixel-by-pixel"

And after PATCHv3 5/9:

	/*
	 * The planes are composed line-by-line to avoid heavy memory usage. It is a necessary
	 * complexity to avoid poor blending performance.
	 *
	 * The function pixel_read_line callback is used to read a line, using an efficient 
	 * algorithm for a specific format, into the staging buffer.
	 */

Kind regards,
Louis Chauvet

> Best Regards,
> ~Arthur Grillo

[...]

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com