commit: 9855d8ce41a7801548a05d844db2f46c3e810166 From: Stefan Bader <[email protected]> Date: Tue, 22 Jan 2013 13:37:21 +0100 Subject: 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 <[email protected]> Cc: 3.7+ <[email protected]> Acked-by: Borislav Petkov <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]> --- drivers/acpi/processor_perflib.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c index 836bfe0..53e7ac9 100644 --- a/drivers/acpi/processor_perflib.c +++ b/drivers/acpi/processor_perflib.c @@ -340,6 +340,13 @@ static void amd_fixup_frequency(struct acpi_processor_px *px, int i) if ((boot_cpu_data.x86 == 0x10 && boot_cpu_data.x86_model < 10) || boot_cpu_data.x86 == 0x11) { rdmsr(MSR_AMD_PSTATE_DEF_BASE + index, lo, hi); + /* + * MSR C001_0064+: + * Bit 63: PstateEn. Read-write. If set, the P-state is valid. + */ + if (!(hi & BIT(31))) + return; + fid = lo & 0x3f; did = (lo >> 6) & 7; if (boot_cpu_data.x86 == 0x10) -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
