linux-kernel - Re: [RFC PATCH 00/16] drm/rockchip: Rockchip EBC ("E-Book Controller") display driver

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Message-ID: <1790161.aHo8FjPgqx@archbook>
Date:   Thu, 21 Apr 2022 09:10:15 +0200
From:   Nicolas Frattaroli <frattaroli.nicolas@...il.com>
To:     Samuel Holland <samuel@...lland.org>,
        Andreas Kemnade <andreas@...nade.info>
Cc:     Heiko Stübner <heiko@...ech.de>,
        Sandy Huang <hjc@...k-chips.com>,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        Alistair Francis <alistair@...stair23.me>,
        Ondřej Jirman <x@....cz>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Liang Chen <cl@...k-chips.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Michael Riesch <michael.riesch@...fvision.net>,
        Peter Geis <pgwipeout@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/16] drm/rockchip: Rockchip EBC ("E-Book Controller") display driver

On Donnerstag, 21. April 2022 08:43:38 CEST Andreas Kemnade wrote:
> On Wed, 13 Apr 2022 17:19:00 -0500
> Samuel Holland <samuel@...lland.org> wrote:
> > Blitting/Blending in Software
> > =============================
> > There are multiple layers to this topic (pun slightly intended):
> >  1) Today's userspace does not expect a grayscale framebuffer.
> >     Currently, the driver advertises XRGB8888 and converts to Y4
> >     in software. This seems to match other drivers (e.g. repaper).
> > 
> >  2) Ignoring what userspace "wants", the closest existing format is
> >     DRM_FORMAT_R8. Geert sent a series[4] adding DRM_FORMAT_R1 through
> >     DRM_FORMAT_R4 (patch 9), which I believe are the "correct" formats
> >     to use.
> >
> hmm R=red? That sounds strange. I am unsure whether doing things with
> lower bit depths actually really helps. 

Hi,

for single-component formats, the name of the component plays
practically no role. Even if said component was really red,
it makes little difference to either side.

For example, the OpenGL straight up refers to all single component
image formats as only using the red component:

	OpenGL only allows "R", "RG", "RGB", or "RGBA"; other
	combinations are not allowed as internal image formats.

from https://www.khronos.org/opengl/wiki/Image_Format

In truth it would of course be nice if the world agreed on
not making the name of data structures imply some way they
are to be processed, but humanity hasn't gotten there yet.

> 
> Regards,
> Andreas
> 

Regards,
Nicolas Frattaroli