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 15:19:58 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <maxime@...no.tech>,
        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>,
        Mark Brown <broonie@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux PWM List <linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] drm/tiny: Add driver for Solomon SSD1307 OLED displays

Hi Javier,

On Fri, Feb 4, 2022 at 2:43 PM Javier Martinez Canillas
<javierm@...hat.com> wrote:
> This patch series adds a DRM driver for the Solomon OLED SSD1305, SSD1306,
> SSD1307 and SSD1309 displays. It is a port of the ssd1307fb fbdev driver.

I gave it a try on an Adafruit FeatherWing 128x32 OLED, connected to an
OrangeCrab ECP5 FPGA board running a 64 MHz VexRiscv RISC-V softcore.

Findings:
  - Kernel size increased by 349 KiB,
  - The "Memory:" line reports 412 KiB less memory,
  - On top of that, "free" shows ca. 92 KiB more memory in use after
    bootup.
  - The logo (I have a custom monochrome logo enabled) is no longer shown.
  - The screen is empty, with a (very very slow) flashing cursor in the
    middle of the screen, with a bogus long line next to it, which I can
    see being redrawn.
  - Writing text (e.g. hello) to /dev/tty0, I first see the text,
    followed by an enlargement of some of the characters.
  - "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.

So while the displays seems to be initialized correctly, it looks like
there are some serious bugs in the conversion from xrgb8888 to
monochrome.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds