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List:       linux-kernel
Subject:    Re: [PATCH] add legacy I/O and memory access routines to /proc/bus/pci API
From:       Jesse Barnes <jbarnes () engr ! sgi ! com>
Date:       2004-12-15 17:00:18
Message-ID: 200412150900.18890.jbarnes () engr ! sgi ! com
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On Wednesday, December 15, 2004 12:57 am, Benjamin Herrenschmidt wrote:
> > I think by "legacy I/O space", you mean specifically "legacy
> > I/O *port* space", right?  Maybe there's no current use for it,
> > but I can imagine supporting MMIO accesses this way, too.
>
> Legacy IO ports, there should be one space per PCI domain. There is also
> legacy ISA memory space though on some ppc's, this doesn't exist at all.
> I suspect we want to expose both in a way.

This interface exports both.

> > On i386, anyway ;-)  But on ia64, we support multiple 64k I/O port
> > spaces (one of them being the 0-64K space that corresponds to the
> > i386 "legacy" space).  Shouldn't we be able to access them with this
> > interface, too?
>
> We should imho. On ppc, we have a 64k space per domain. One of the main
> set of HW that has use for these are VGA cards. It's perfectly possible
> to have a Mac with an AGP card in the AGP port and a PCI video card in
> one of hte PCI slots, and those are on 2 different domains with
> different legacy (0...64k) IO spaces.
>
> We defininitely want whatever interface we define to deal with that.

Good, because that's exactly what it does.  The arch is responsible for 
returning the legacy I/O port or legacy ISA memory base address given a 
pci_dev, which is used as a base for the page offset passed into mmap.  So 
e.g. mmap(..., 0xa0000) after doing ioctl(fd, PCIIOC_MMAP_IS_LEGACY_MEM, ...) 
would get you the VGA framebuffer for the device corresponding to 'fd'.

> There is some work done by Jon Smirl in this area (a VGA access
> arbitration driver).

I think Dave Airlie did a version of the vga class driver, and the backend 
used for /proc/bus/pci could be used for both drivers.  I'm 
using /proc/bus/pci because it's available now and nearly good enough (i.e. 
this patch was all I needed to get going).

Anyway, I'll post another version with Bjorn's suggestion about the ioctl for 
choosing config or legacy I/O port read/writes, since it looks like the rest 
of your concerns are dealt with.

Thanks,
Jesse
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