linux-kernel - Re: [RFC PATCH 08/12] PAT 64b: coherent mmap and sysfs bin ioctl

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Date:	Mon, 17 Dec 2007 13:41:37 +0100
From:	Andi Kleen <ak@....de>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Greg KH <gregkh@...e.de>, David Miller <davem@...emloft.net>,
	venkatesh.pallipadi@...el.com, ebiederm@...ssion.com,
	rdreier@...co.com, torvalds@...ux-foundation.org,
	airlied@...net.ie, davej@...hat.com, mingo@...e.hu,
	tglx@...utronix.de, hpa@...or.com, akpm@...ux-foundation.org,
	arjan@...radead.org, jesse.barnes@...el.com,
	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com
Subject: Re: [RFC PATCH 08/12] PAT 64b: coherent mmap and sysfs bin ioctl

On Mon, Dec 17, 2007 at 08:57:50AM +1100, Paul Mackerras wrote:
> Greg KH writes:
> 
> > Ok, sorry, it wasn't blindingly obvious that this was for pci sysfs
> > devices that are mmaped, that makes a bit more sense.
> > 
> > But I'd like to see what ioctl is wanted here first.
> 
> I believe the ioctl would be to set whether the mapping goes to I/O or
> memory space, 

x86 cannot really access IO space through mmap so no that wasn't planned

The main planned use was to get the translated bus address (after IOMMU)
for a mapping and to set the caching modes.

> So the alternative to the ioctl would be to have multiple files in
> sysfs, one per combination of modes -- i.e., 4 files, or 3 if we
> exclude the "I/O with write combining" mode, which would be
> reasonable.

At least for the IOMMU translation case that wouldn't work.

-Andi
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