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

[Andi Kleen]

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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