From: Stefan Bader Date: Tue, 22 Jan 2013 12:37:21 +0000 (+0100) Subject: ACPI: Check MSR valid bit before using P-state frequencies X-Git-Tag: v3.8-rc5~6^2~1 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9855d8ce41a7801548a05d844db2f46c3e810166;p=pandora-kernel.git ACPI: Check MSR valid bit before using P-state frequencies To fix incorrect P-state frequencies which can happen on some AMD systems f594065faf4f9067c2283a34619fc0714e79a98d "ACPI: Add fixups for AMD P-state figures" introduced a quirk to obtain the correct values by reading from AMD specific MSRs. This did cause a regression when running a kernel using that quirk under Xen which does (currently) not pass through MSR reads to the HW. Instead the guest gets a 0 in return. And this seems to cause a failure to initialize the ondemand governour (hard to say for sure as all P-states appear to run at the same frequency). While this should also be fixed in the hypervisor (to allow a guest to read that MSR), this patch is intended to work around the issue in the meantime. In discussion it turned out that indeed real HW/BIOSes may choose to not set the valid bit and thus mark the P-state as invalid. So this could be considered a fix for broken BIOSes that also works around the issue on Xen. Signed-off-by: Stefan Bader Cc: 3.7+ Acked-by: Borislav Petkov Signed-off-by: Rafael J. Wysocki --- Reading git-diff-tree failed