[Xen-devel] [PATCH] ACPI: Add fixups for AMD P-state figures.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

This a copy-n-paste from two Linux git commits:

- f594065faf4f9067c2283a34619fc0714e79a98d
  ACPI: Add fixups for AMD P-state figures
- 9855d8ce41a7801548a05d844db2f46c3e810166
  ACPI: Check MSR valid bit before using P-state frequencies

The issue is that "some AMD systems may round the frequencies in
ACPI tables to 100MHz boundaries. We canobtain the real
frequencies from MSRs, so add a quirk to fix these frequencies up
on AMD systems." (from f594065..)

In discussion (around 9855d8..) "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." (from 9855d8..)

I've tested it under Dell Inc. PowerEdge T105 /0RR825, BIOS 1.3.2
08/20/2008 where this quirk can indeed be observed.

CC: stefan.bader@xxxxxxxxxxxxx
CC: bp@xxxxxxx
CC: borislav.ostrovsky@xxxxxxxxxx
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 xen/arch/x86/acpi/cpufreq/powernow.c | 38 ++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/xen/arch/x86/acpi/cpufreq/powernow.c 
b/xen/arch/x86/acpi/cpufreq/powernow.c
index a9b7792..0eaa16c 100644
--- a/xen/arch/x86/acpi/cpufreq/powernow.c
+++ b/xen/arch/x86/acpi/cpufreq/powernow.c
@@ -146,7 +146,43 @@ static int powernow_cpufreq_target(struct cpufreq_policy 
*policy,
 
     return 0;
 }
+#define MSR_AMD_PSTATE_DEF_BASE     0xc0010064
+static void amd_fixup_frequency(struct xen_processor_px *px)
+{
+       u32 hi, lo, fid, did;
+       int index = px->control & 0x00000007;
+
+       if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
+               return;
+
+       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 & (1UL << 31)))
+            return;
+
+               fid = lo & 0x3f;
+               did = (lo >> 6) & 7;
+               if (boot_cpu_data.x86 == 0x10)
+                       px->core_frequency = (100 * (fid + 0x10)) >> did;
+               else
+                       px->core_frequency = (100 * (fid + 8)) >> did;
+       }
+}
+
+static void amd_fixup_freq(struct processor_performance *perf)
+{
 
+    int i;
+
+    for (i = 0; i < perf->state_count; i++)
+        amd_fixup_frequency(&perf->states[i]);
+
+}
 static int powernow_cpufreq_verify(struct cpufreq_policy *policy)
 {
     struct acpi_cpufreq_data *data;
@@ -253,6 +289,8 @@ static int powernow_cpufreq_cpu_init(struct cpufreq_policy 
*policy)
 
     policy->governor = cpufreq_opt_governor ? : CPUFREQ_DEFAULT_GOVERNOR;
 
+    amd_fixup_freq(perf);
+
     /* table init */
     for (i = 0; i < perf->state_count && i <= max_hw_pstate; i++) {
         if (i > 0 && perf->states[i].core_frequency >=
-- 
1.8.0.2


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