linux-kernel - Re: VESA and VGA16 framebuffer drivers clash sometimes

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Date:	Fri, 20 Apr 2012 13:12:10 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Boszormenyi Zoltan <zboszor@...hu>
Cc:	linux-kernel@...r.kernel.org,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>
Subject: Re: VESA and VGA16 framebuffer drivers clash sometimes

2012/4/20 Boszormenyi Zoltan <zboszor@...hu>:
> on an embedded x86 board with Intel Atom, text on vesafb
> gets distorted if both vesafb and vga16fb are compiled in.
> The strange thing is that it doesn't happen all the time but
> about once out of 15 boots.
>
> The distortion looks like this:
> http://www.postgresql-support.de/private/IMG_7221.jpg
>
> The relevant kernel messages:
>
> Apr 13 11:14:30 term002 kernel: vesafb: mode is 800x600x16, linelength=1600,
> pages=7
> Apr 13 11:14:30 term002 kernel: vesafb: scrolling: redraw
> Apr 13 11:14:30 term002 kernel: vesafb: Truecolor: size=0:5:6:5,
> shift=0:11:5:0
> Apr 13 11:14:30 term002 kernel: vesafb: framebuffer at 0xa0000000, mapped to
> 0xdf580000, using 1875k, total 8128k
> Apr 13 11:14:30 term002 kernel: Console: switching to colour frame buffer
> device 100x37
> Apr 13 11:14:30 term002 kernel: fb0: VESA VGA frame buffer device
> Apr 13 11:14:30 term002 BOOTLOG: Terminal startup
> Apr 13 11:14:30 term002 kernel: vga16fb: mapped to 0xc00a0000
> Apr 13 11:14:30 term002 kernel: fbcon: VGA16 VGA (fb1) is primary device
> Apr 13 11:14:30 term002 kernel: fbcon: Remapping primary device, fb1, to tty
> 1-63
> Apr 13 11:14:30 term002 kernel: fb1: VGA16 VGA frame buffer device
>
> It's strange that vga16fb is always detected as primary
> and vesafb gets remapped to fb1 even when there is no
> screen distortion. The kernel is compiled for SMP.

IIRC, the request_region()/request_mem_region() calls in vga16fb.c that would
avoid this were removed several years ago. Unfortunately I don't remember
anymore why. Google or full-history-linux may help you...

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
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