linux-kernel - Re: [PATCH v3 2/3] drm/st7571-i2c: add support for Sitronix ST7571 LCD controller

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Message-ID: <CAMuHMdVF+QOm5JZf+1ztu=aEW_3+aFkpThzsLWMv3D=Anny_Tg@mail.gmail.com>
Date: Fri, 11 Apr 2025 08:47:33 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Javier Martinez Canillas <javierm@...hat.com>
Cc: Marcus Folkesson <marcus.folkesson@...il.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Thomas Zimmermann <tzimmrmann@...e.de>
Subject: Re: [PATCH v3 2/3] drm/st7571-i2c: add support for Sitronix ST7571
 LCD controller

On Wed, 9 Apr 2025 at 16:16, Javier Martinez Canillas
<javierm@...hat.com> wrote:
> Marcus Folkesson <marcus.folkesson@...il.com> writes:
> > On Wed, Apr 09, 2025 at 11:43:54AM +0200, Javier Martinez Canillas wrote:
>
> [...]
>
> >>
> >> Likely you will need to define more stuff to be specific for each entry, maybe
> >> you will need different primary plane update handlers too. Similar to how I had
> >> to do it the ssd130x driver to support all the Solomon OLED controller families:
> >>
> >> https://elixir.bootlin.com/linux/v6.11/source/drivers/gpu/drm/solomon/ssd130x.c#L1439
> >
> > Thanks, that sounds like a good idea.
> >
> > I've now experimenting with XRGB8888, and, well, it works. I guess.
> > The thresholds levels in the all conversion steps for  XRGB8888 -> 8 bit grayscale -> monochrome
> > makes my penguin look a bit boring.
> >
> > But I guess that is expected.
>
> Yeah, the XRGB8888 version is a boring indeed comparing with the C1 one...

To see the nice monochrome penguin logo, fb-helper needs to gain
support for R1 first...

> The drm_fb_xrgb8888_to_mono() helper is very naive and just uses a very
> naive midpoint thresholding to choose if the pixel should be 1 or 0. So
> there is a lot of information lost there unfortunately.

In theory, it could use Floyd–Steinberg dithering, like I did for modetest.
However, given the display receives partial updates from damage clips,
it will look ugly, and may flicker.

> But that's what I did for ssd130x, to at least have a working driver. Then
> support for R1 (for ssd130x family) and R4 (for the ssd132x family) could
> be added as follow-ups. I never did it but Geert has some patches for this.

[1] needs an update, and still more rework to make them acceptable.

> > Please compare
> > https://www.marcusfolkesson.se/xrgb8888.png
> > and
> > https://www.marcusfolkesson.se/c1.png

Yep, the latter is using the correct logo.

[1]  "[PATCH v2 0/8] drm: fb-helper/ssd130x: Add support for DRM_FORMAT_R1"
    https://lore.kernel.org/all/cover.1692888745.git.geert@linux-m68k.org/

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds