linux-kernel - Re: [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

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Date:   Tue, 8 Feb 2022 15:18:14 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Maxime Ripard <maxime@...no.tech>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED
 displays

On Tue, Feb 08, 2022 at 04:10:49PM +0100, Javier Martinez Canillas wrote:
> On 2/8/22 15:19, Geert Uytterhoeven wrote:

> >   - "time ls" on the serial console (no files in the current directory,
> >     so nothing to print) increases from 0.86s to 1.92s, so the system is
> >     more loaded.  As ssd1307fb relied on deferred I/O too, the slowdown
> >     might be (partly) due to redrawing of the visual artefacts
> >     mentioned above.

> I was trying to first have the driver and then figure out how to optimize
> it. For v3 I'm using regmap to access instead of the I2C layer directly.

> I noticed that this is even slower but it makes the driver more clean and
> allows to support both I2C and SPI (untested but will include it as a WIP).

I wouldn't have expected regmap to add huge overhead relative to I2C,
partly predicated on I2C being rather slow itself.  There will be some
overhead for concurrency protection and data marshalling but for I2C
clocked at normal speeds it's surprising.

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