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Message-ID: <e9c3a7c20601200947t1d3c1c4eybea2adb97a10c92c@mail.gmail.com>
Date: Fri, 20 Jan 2006 10:47:39 -0700
From: Dan Williams <dan.j.williams@gmail.com>
To: linux-arm-kernel@lists.arm.linux.org.uk, linux-kernel@vger.kernel.org
Subject: hugetlbfs on ARM / how to mmap() 36-bit PCI memory?
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I just went through an experiment trying to mmap a PCI resource via
the /sys/bus/pci/devices/<device name>/resource[n] on a XSC3 platform.
 I discovered, correct me if I am wrong, that remap_pfn_range only
acts on 2nd level (4K) pte's.  On this platform PCI memory is only
available at a 36-bit physical address.

In looking for an answer I found this post from Deepak in the thread:
"clean way to support >32bit addr on 32bit CPU "
http://marc.theaimsgroup.com/?t=110540164100006&r=1&w=2

<snip>
Not doable. I believe PAE allows for normal 4K pages to be used when
mapping > 32-bits. XSC3 and ARMv6 only allow for > 32 bit addresses
when using 16MB pages (supersections), so we need to instead use
the hugetlb approach.

~Deepak
</snip>

Questions
1) Currently ARM does not appear to have support for hugetlbfs, is
this in the works / any pointers to help get me started with the code?
2) Does the hugetlbfs interface support PCI memory or is it only meant for RAM?
3) Is there a better approach than hugetlb to mmap PCI space in this scenario?

Thanks,

Dan
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