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Re: linux-mips fbdev

To: nsauzede <nsauzede@online.fr>
Subject: Re: linux-mips fbdev
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Sun, 22 Dec 2002 14:58:48 +0100 (MET)
Cc: linux-mips <linux-mips@linux-mips.org>
In-reply-to: <013b01c2a16c$68385f60$0100a8c0@yak>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
On Thu, 12 Dec 2002, nsauzede wrote:
> I've got an Indy running linux-mips and I wonder if fbdev exists/is possible 
> on this platform.
> If I remember well, direct framebuffer mmaping like on intel platforms for 
> example is not possible because Video Ram is hidden behind SGI custom video 
> chips, and video accesses are done by some magic incantations..

Yes, you always have to use the graphics accelerator.

> But the fact is that I can run linux on my box, a gfx penguin logo appears at 
> boot, and I can enjoy a huge beautifull mc on the console, so I guess some 
> "kind" of framebuffer is there, but not the full-blown Geert's-et-al stuff.

:-)

> So my question is : would it be feasible/easy to implement some kind of 
> "stubs" to, at least, simulate a straight framebuffer, with full /dev/fb0 
> stuff, so I could port my fbdev userspace stuff to my Indy ???

By using the tricks also used in vga256fb (cfr.
http://www.kyuzz.org/antirez/vga256fb.html), you can emulate a normal linear
frame buffer and use the Indy's graphics accelerator to update the screen.
But it will be slow.

An alternative is to use mmap() tricks to find out what's updated in the fake
linear frame buffer, and update the screen afterwards.

Or program the Indy graphics accelerator directly from user space :-)

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


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