Re: newbie: fb specs and indirect VRAM access

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

On Thu, 21 Aug 2008, Jorge Marques Pelizzoni wrote:
> A few days ago I sent the message below asking about framebuffer device
> documentation and explaining my specific situation. Nobody aswered and I
> wonder why. If those are not questions for this list, can someone please
> redirect me to the right forum?

I had hoped somebody else would find time to respond ;-)

> Jorge Marques Pelizzoni escreveu:
> > I am considering implementing a frame buffer device for a mobile platform
> > (LPC2400 on uCLinux) that, as far as I can tell, seems to lack one. Well,
> > I am a newbie to all things frame buffer-related (though familiar with
> > kernel/device module implementation) and would most appreciate it if you
> > could answer the following questions:
> >
> > 1 - are there documents specifying frame buffer devices and how
> > applications are expected to handle them (in short, their API)?

linux/Documentation/fb/framebuffer.txt
linux/include/linux/fb.h

> > 2 - my CPU cannot address "real" VRAM directly, all control being carried
> > out by means of a parallel interface. I gathered that an fb user is
> > expected to write to (virtual) VRAM directly via a pointer provided by the
> > driver and never notifies the driver of changes. Have you seen such a
> > set-up before and do you think these requirements can be reconciled? The
> > only way round this I can currently see is making the driver periodically
> > check the virtual VRAM for changes and transmit only changed parts. All in
> > all, a costly operation, as everything must be carried out by the same
> > CPU. Could whatever is used to implement mmap be called into play (without
> > whatever is used to implement msync)?

linux/Documentation/fb/deferred_io.txt

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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