Re: VGA PCI IO port reservations

[Jeff Garzik <jgarzik@mandrakesoft.com>]

Russell King wrote:
> 
> Brian Gerst writes:
> > This is an artifact from the ISA 10-bit IO bus.  Many ISA cards do not
> > decode all 16 address bits so you get aliases of the 0x100-0x3ff region
> > throughout IO space.  PCI cards should only use the first 256 ports of
> > any 1k block to avoid aliases unless they claim the base alias.  For
> > example, all the xxe8 addresses for the S3 are aliases of 0x02e8 to an
> > ISA card.  Video cards are an exception to the general rule because they
> > have to support all the legacy VGA crap.
> 
> No.  All xxe8 addresses access specific registers.  For example:
> 
>   0x9ea8 is the drawing command
>   0xa2e8 is the background colour register
>   0xa6e8 is the foreground colour register
> 
> So, as you see they aren't aliases.

Oh yeah, if you are writing for S3 specifically, you can do 100% MMIO,
and simply turn off all I/O decoding.  Check out Keith Packard's
kdrive/s3trio in the XFree86 tree...

	Jeff


-- 
Jeff Garzik             |
Building 1024           | The chief enemy of creativity is "good" sense
MandrakeSoft            |          -- Picasso
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