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 16:40:12 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "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>,
        Mark Brown <broonie@...nel.org>,
        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 2/8/22 16:23, Geert Uytterhoeven wrote:

[snip]

>>>   - The logo (I have a custom monochrome logo enabled) is no longer shown.
>>
>> I was able to display your tux monochrome with ./fbtest -f /dev/fb1 test004
> 
> I meant the kernel's logo (FB_LOGO_*),. Obviously you need to enable
> a smaller one, as the default 80x80 logo is too large, and thus can't
> be drawn on your 128x64 or my 128x32 display.
>

That makes sense.
 
>>>   - 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.
>>
>> So far I was mostly testing using your fbtest repo tests and all of them
>> (modulo test009 that says "Screen size too small for this test").
>>
>> But I've tried now using as a VT and I see the same visual artifacts. I
>> wonder what's the difference between fbcon and the way your tests use
>> the fbdev API.
> 
> Fbcon does small writes to the shadow frame buffer, while fbtest
> writes to the mmap()ed /dev/fbX, causing a full page to be updated.
>

I see. Thanks for the information.

Best regards, -- 
Javier Martinez Canillas
Linux Engineering
Red Hat