>>> On 21.07.15 at 02:57, <kevin.t...@intel.com> wrote: >> From: Andrew Cooper [mailto:am...@hermes.cam.ac.uk] On Behalf Of Andrew > Cooper >> Sent: Monday, July 20, 2015 4:21 PM >> >> On 20/07/2015 02:28, Tian, Kevin wrote: >> >> From: Ting-Wei Lan [mailto:lant...@gmail.com] >> >> Sent: Saturday, July 18, 2015 3:06 AM >> >> >> >> When using Linux >= 3.19 (commit 47591df) as dom0 on some Intel Ironlake >> >> devices, It is possible to encounter graphics issues that make screen >> >> unreadable or crash the system. It was reported in freedesktop bugzilla: >> >> >> >> https://bugs.freedesktop.org/show_bug.cgi?id=90037 >> >> >> >> As we still cannot find a proper fix for this problem, this patch adds >> >> iommu=igfx_off option that is similar to Linux intel_iommu=igfx_off for >> >> users to manually workaround the problem. >> >> >> >> Signed-off-by: Ting-Wei Lan <lant...@gmail.com> >> > Since igfx works before, I'd think a more proper fix should be on the >> > bisected Linux commit or i915 to have two working correctly together. >> > Otherwise this patch is just hiding problem. >> >> The linux commit is the one which actually fixes PAT support for Linux >> under Xen. >> >> It will cause the i915 driver to actually get WC mappings when it asks >> for them. > > This is the part which I don't quite understand. WC is essentially an UC > attribute with write buffer to accelerate the write efficiency. There > should be no correctness problem to use either WC or UC if i915 driver > wants WC.
"Should" is too weak a term here: Using WC on the wrong piece of memory or without the necessary fencing can imo very well cause correctness problems (which would be hidden by WC -> UC conversion behind the driver's back). Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
