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

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Message-ID: <875xjb2jeg.fsf@minerva.mail-host-address-is-not-set>
Date: Fri, 11 Apr 2025 10:26:47 +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 Marcus,

[...]

>> static const struct of_device_id st7571_of_match[] = {
>> 	/* monochrome displays */
>> 	{
>> 		.compatible = "sinocrystal,sc128128012-v01",
>> 		.data = monochrome_formats,
>> 	},
>> ...
>>         /* grayscale displays */
>> 	{
>> 		.compatible = "foo,bar",
>> 		.data = grayscale_formats,
>> 	},
>> };
>
> A comment for v4:
>
> I think I will go for a property in the device tree. I've implemented
> board entries as above, but I'm not satisfied for two reasons:
>
> 1. All other properties like display size and resolution are already
>    specified in the device tree. If I add entries for specific boards,
>    these properties will be somehow redundant and not as generic.
>
> 2. I could not find a ST7571 with a grayscale display as a off-the-shelf
>    product.

Sure, that makes sense to me.

Can I ask if you could still add reasonable default values that could be set
in the device ID .data fields ?

As mentioned, I've a ST7567 based LCD and a WIP driver for it. But I could
just drop that and use your driver, since AFAICT the expected display data
RAM format is exactly the same than when using monochrome for the ST7571.

But due the ST7567 only supporting R1, it would be silly to always have to
define a property in the DT node given that does not support other format.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat