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

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Date:   Wed, 9 Feb 2022 14:22:33 +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 03:17:06PM +0100, Javier Martinez Canillas wrote:
> On 2/9/22 14:43, Mark Brown wrote:

> > Unless the device supports power being physically omitted regulator
> > usage should not be optional, it's just more code and a recipie for poor
> > error handling.

> The device has a VCC pin but in most cases this is just connected to a
> power provided by the board in its pinout header. For example, I've it
> connected to a rpi4 3.3v pin.

That sounds like a very common configuration.

> 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 old ssd1307fb fbdev driver also had this as optional and I wanted to
> keep the new driver as backward compatible. But I understand now that is
> not describing the hardware properly by making this regulator optional.

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

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