On Fri, May 01, 2020 at 11:37:12AM +0100, Mark Rutland wrote: > On Fri, May 01, 2020 at 09:05:00AM +0200, Greg KH wrote: > > On Thu, Apr 30, 2020 at 04:19:22PM -0500, Jeremy Linton wrote: > > > On arm64, and possibly other architectures, requesting > > > IO coherent memory may return Normal-NC if the underlying > > > hardware isn't coherent. If these pages are then > > > remapped into userspace as Normal, that defeats the > > > purpose of getting Normal-NC, as well as resulting in > > > mappings with differing cache attributes. > > > > What is "Normal-NC"? > > Arm terminology for "Normal Non-Cacheable"; it might be better to say > something like: > > On some architectures (e.g. arm64) an IO coherent mapping may use > non-cachable attributes if the relevant device is cache coherent. > If userspace mappings are cacheable, these may not be coherent with > non-cacheable mappings. On arm64 this is the case for Normal-NC and > Normal (cacheable) mappings. That's better, but it doesn't answer any of my other questions on this patch :) thanks, greg k-h
