linux-mips fbdev

linux-mips fbdev

[nsauzede]

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Hi list !

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..

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 ???

Sorry if the answer is obvious..

Thanks so much to all of you linux-mips-gurus for what has been done !!

Nicolas Sauzede.

ps : in case the answer is : No; would it be hard for newbies like me to enable userspace apps to access video screen (just like with fbdev, but without it), ie : be able to do some bitblt() or such ? I've tried to copy/paste some kernel fragments that "seems" to do the voodoo-like video accesses, just to set some pixels on screen, but all I could obtain was : entire screen corrupted or even crash (no BSOD here though <whew> ;)


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Re: linux-mips fbdev

[Geert Uytterhoeven]

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

Re: linux-mips fbdev

[nsauzede]

Hello !
Thank you so much for your response !! :-)

> Yes, you always have to use the graphics accelerator.

Ok

> 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.

This link is really interesting, thanks !

> 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 :-)

Hmm, may be that would be the best I have to do for now, at least in order
to get familiarized with the "Indy graphics accelerator" you're talking
about...
Any pointers ?? All I could find about it was kernel code fragments found in
the linux mips source, that crashed my indy
when trying to play with pixels in user mode..
But, maybe you're not implied a lot in Indy graphics, and I'm sorry if I
bother  you to much with my problems !!

> Gr{oetje,eeting}s,
>
> Geert

Thank you !

Nicolas Sauzede.