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

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Javier,

On Tue, Feb 8, 2022 at 4:10 PM Javier Martinez Canillas
<javierm@redhat.com> wrote:
> On 2/8/22 15:19, Geert Uytterhoeven wrote:
> > On Fri, Feb 4, 2022 at 2:43 PM Javier Martinez Canillas
> > <javierm@redhat.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.
>
> 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.

> >   - 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.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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