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

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Message-ID: <87zfgpe7zg.fsf@minerva.mail-host-address-is-not-set>
Date: Wed, 09 Apr 2025 16:15:47 +0200
From: Javier Martinez Canillas <javierm@...hat.com>
To: Marcus Folkesson <marcus.folkesson@...il.com>
Cc: 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

Marcus Folkesson <marcus.folkesson@...il.com> writes:

> Hello Javier,
>
> 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...

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.

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.

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

Nice pictures!

>> -- 
>> Best regards,
>> 
>> Javier Martinez Canillas
>> Core Platforms
>> Red Hat
>> 
>
> Best regards,
> Marcus Folkesson

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat