linux-kernel - Re: [PATCH 0/2] drm/panel: Add support for the Sitronix ST7789V

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Date:   Mon, 6 Feb 2017 12:29:31 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 0/2] drm/panel: Add support for the Sitronix ST7789V

Den 06.02.2017 11.39, skrev Maxime Ripard:
> Hi Noralf,
>
> On Fri, Feb 03, 2017 at 07:48:51PM +0100, Noralf Trønnes wrote:
>> Den 03.02.2017 10.59, skrev Maxime Ripard:
>>> Hi,
>>>
>>> Here is an attempt at supporting the ST7789V LCD controller from Sitronix.
>> What happens if there's another panel driven by ST7789V that needs
>> a different controller initialization?
> You know those panels / controllers much better than I do, but why
> would that be the case?
>
>> Maybe it's better to name it after the panel, not the controller.
> I guess you could also use that panel directly without the controller?

A controller can drive many different panels that can require different
initializations. I faced that with staging/fbtft, when I wrote
controller drivers having initialization code, and then came across
displays with the same controller but with a different initialization.

Trying to write controller drivers for these controllers is very
difficult with all the possible permutations. On top of that we have
those undocumented commands/registers.

Some panels come with embedded controllers, in which case it makes
sense to write a driver for the panel.

But if the panel and controller are separate, then I don't know. Maybe
the chance of coming across two uncompatible ST7789V and panel
combinations in drm/panel is extremly low.

Noralf.