Re: [Linaro-mm-sig] [RFC 0/2] ARM: DMA-mapping & IOMMU integration

On Mon, 13 Jun 2011 10:55:59 -0700 "Michael K. Edwards" m.k.edwards@gmail.com wrote:

As far as I can tell, there is not yet any way to get real cache-bypassing write-combining from userland in a mainline kernel, for x86/x86_64 or ARM.

Well only if things are really broken. sysfs exposes _wc resource files to allow userland drivers to map a given PCI BAR using write combining, if the underlying platform supports it.

Similarly, userland mapping of GEM objects through the GTT are supposed to be write combined, though I need to verify this (we've had trouble with it in the past).