linux-kernel - Re: [RFC PATCH] drm/tiny: Add support for Sitronix ST7539

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Message-ID: <3f4e9dfa-6373-4b34-8097-48c870e69daa@lechnology.com>
Date: Wed, 3 Jul 2024 11:07:35 -0500
From: David Lechner <david@...hnology.com>
To: Christian Eggers <ceggers@...i.de>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc: Noralf Trønnes <noralf@...nnes.org>,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH] drm/tiny: Add support for Sitronix ST7539

On 7/3/24 9:05 AM, Christian Eggers wrote:
> Based on the existing ST7586 driver. But the ST7539 ...
> - is monochrome only
> - has 8 VERTICAL pixels per byte
> - doesn't support any MIPI DCS commands
> - has (a few) 16 bit commands
> - doesn't support setting a clipping rect when writing to the RAM
> - doesn't support rotation (only mirroring of X and/or Y axis)
> 
> Questions/TODO:

To start with, I would suggest reading [1]. This patch is really hard to
read because it isn't properly formatted. If you don't change the patch,
you can resend it as [RFC PATCH RESEND] using `git send-email`, or if you
do change the patch before re-sending, e.g. because you fixed checkpatch
style issues, just call it v2.

[1]: https://www.kernel.org/doc/html/latest/process/submitting-patches.html

> - should drivers for such old displays be mainlined?

If it is actually going to be used and you are willing to maintain it,
then yes.

> - shall I use mipi_dbi_ although the display doesn't implement MIPI DCS
> (and has some 16 bit commands)?
> - can the conversion to 8 vertical pixels/byte (taken from
> solomon/ssd130x.c) be avoided / simplified / made more efficient?
> - how to implement setting of the display contrast (required by my
> application)?

I see that ssd130x_update_bl() is using brightness to control
contrast. Don't know if it that is the best way though.

> - add device tree binding
> 
> Signed-off-by: Christian Eggers <ceggers@...i.de>
> ---