linux-kernel - Re: [PATCH v3 3/7] drm: Add driver for Solomon SSD130X OLED displays

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Date:   Wed, 9 Feb 2022 15:03:57 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Noralf Trønnes <noralf@...nnes.org>,
        Maxime Ripard <maxime@...no.tech>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-fbdev@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>,
        dri-devel@...ts.freedesktop.org, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Lee Jones <lee.jones@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v3 3/7] drm: Add driver for Solomon SSD130X OLED displays

On Wed, Feb 09, 2022 at 03:50:13PM +0100, Javier Martinez Canillas wrote:
> On 2/9/22 15:22, Mark Brown wrote:
> > On Wed, Feb 09, 2022 at 03:17:06PM +0100, Javier Martinez Canillas wrote:

> >> I guess in that case what we should do then is to just have a regulator
> >> fixed as the vbat-supply in the Device Tree, that's regulator-always-on.

> > Generally I'd suggest labelling things with whatever the supply is
> > called in the board's schematics/documentation, that tends to make
> > things clearer and easier to follow.

> The display controller datasheet and schematics mention VBAT as the power
> supply but the documentation says that it's just connected to VCC and the
> label in the display says VCC.

> But I understand why the Device Tree binding and fbdev driver used VBAT
> since that's what the documentation mentions.

What is "the documentation" in this context and how is that distinct
from the datasheet for the display controller?  In general the consumer
driver should be using the name from the datasheet and the regulator
itself should get a regulator-name reflecting the name in the schematic.

> > It is depressingly common to see broken code here, unfortunately
> > graphics drivers seem like one of the most common offendors.

> I'll include a patch for the existing DT binding and mark the vbat-supply
> property as required. Probably we won't be able to change the fbdev driver
> without causing regressions, and I'm not interested in that driver anyways.

There should be little danger of causing regressions given that a dummy
regualtor will be provided when one is missing.

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