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From: "David S. Miller" <davem@redhat.com>
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Date: Thu, 1 Mar 2001 11:09:00 -0800 (PST)
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: <linux-kernel@vger.kernel.org>, <linuxppc-dev@lists.linuxppc.org>
Subject: Re: The IO problem on multiple PCI busses
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Benjamin Herrenschmidt writes:
 > I'm, of course open to any comments about this (in fact, I'd really like
 > some feedback). One thing is that we also need to find a way to pass
 > those infos to userland. Currently, we implement an arch-specific syscall
 > that allow to retreive the IO physical base of a given PCI bus. That may
 > be enough, but we may also want something that match more closely what we
 > do in the kernel.

Same problem on sparc64.  Using a special PCI syscall is fine, _if_ we
all end up using the same one.  However, I would prefer another
mechanism...

I think a cleaner scheme is to allow mmap() on
/proc/bus/pci/${BUS}/${DEVICE} nodes, that is much cleaner and solves
transparently any "different word size between userland and kernel"
issues (specifically 32-bit userlands executing on 64-bit kernels).

I played around with something akin to this, and some of the necessary
Xfree86-4.0.x hackery needed, some time ago.  But I never finished
this.

Later,
David S. Miller
davem@redhat.com

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