[CPUFREQ] powernow-k8: determine exact CPU frequency for HW Pstates

Slightly modified by trenn@suse.de -> only do this on fam 10h and fam 11h.

Currently powernow-k8 determines CPU frequency from ACPI PSS objects, but
according to AMD family 11h BKDG this frequency is just a rounded value:

  "CoreFreq (MHz) = The CPU COF specified by MSRC001_00[6B:64][CpuFid]
  rounded to the nearest 100 Mhz."

As a consequnce powernow-k8 reports wrong CPU frequency on some systems,
e.g. on Turion X2 Ultra:

  powernow-k8: Found 1 AMD Turion(tm)X2 Ultra DualCore Mobile ZM-82
               processors (2 cpu cores) (version 2.20.00)
  powernow-k8:    0 : pstate 0 (2200 MHz)
  powernow-k8:    1 : pstate 1 (1100 MHz)
  powernow-k8:    2 : pstate 2 (600 MHz)

But this is wrong as frequency for Pstate2 is 550 MHz. x86info reports it
correctly:

  #x86info -a |grep Pstate
  ...
  Pstate-0: fid=e, did=0, vid=24 (2200MHz)
  Pstate-1: fid=e, did=1, vid=30 (1100MHz)
  Pstate-2: fid=e, did=2, vid=3c (550MHz) (current)

Solution is to determine the frequency directly from Pstate MSRs instead
of using rounded values from ACPI table.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 21 insertions, 2 deletions

diff --git a/arch/x86/kernel/cpu/cpufreq/powernow-k8.c b/arch/x86/kernel/cpu/cpufreq/powernow-k8.c
index feef10c085a1..f6b32d112357 100644
--- a/arch/x86/kernel/cpu/cpufreq/powernow-k8.c
+++ b/arch/x86/kernel/cpu/cpufreq/powernow-k8.c
@@ -649,6 +649,20 @@ static void print_basics(struct powernow_k8_data *data)
                                 data->batps);
 }
 
+static u32 freq_from_fid_did(u32 fid, u32 did)
+{
+        u32 mhz = 0;
+
+        if (boot_cpu_data.x86 == 0x10)
+                mhz = (100 * (fid + 0x10)) >> did;
+        else if (boot_cpu_data.x86 == 0x11)
+                mhz = (100 * (fid + 8)) >> did;
+        else
+                BUG();
+
+        return mhz * 1000;
+}
+
 static int fill_powernow_table(struct powernow_k8_data *data,
                 struct pst_s *pst, u8 maxvid)
 {
@@ -923,8 +937,13 @@ static int fill_powernow_table_pstate(struct powernow_k8_data *data,
 
                 powernow_table[i].index = index;
 
-                powernow_table[i].frequency =
-                        data->acpi_data.states[i].core_frequency * 1000;
+                /* Frequency may be rounded for these */
+                if (boot_cpu_data.x86 == 0x10 || boot_cpu_data.x86 == 0x11) {
+                        powernow_table[i].frequency =
+                                freq_from_fid_did(lo & 0x3f, (lo >> 6) & 7);
+                } else
+                        powernow_table[i].frequency =
+                                data->acpi_data.states[i].core_frequency * 1000;
         }
         return 0;
 }