powerpc: powernv: Framework to show the correct clock in /proc/cpuinfo

Currently, the code in setup-common.c for powerpc assumes that all
clock rates are same in a smp system. This value is cached in the
variable named ppc_proc_freq and is the value that is reported in
/proc/cpuinfo.

However on the PowerNV platform, the clock rate is same only across
the threads of the same core. Hence the value that is reported in
/proc/cpuinfo is incorrect on PowerNV platforms. We need a better way
to query and report the correct value of the processor clock in
/proc/cpuinfo.

The patch achieves this by creating a machdep_call named
get_proc_freq() which is expected to returns the frequency in Hz. The
code in show_cpuinfo() can invoke this method to display the correct
clock rate on platforms that have implemented this method. On the
other powerpc platforms it can use the value cached in ppc_proc_freq.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

2 files changed, 14 insertions, 4 deletions

diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
index 240b137ce0cf..374abc2e41d7 100644
--- a/arch/powerpc/include/asm/machdep.h
+++ b/arch/powerpc/include/asm/machdep.h
@@ -113,6 +113,8 @@ struct machdep_calls {
         /* Optional, may be NULL. */
         void            (*show_cpuinfo)(struct seq_file *m);
         void            (*show_percpuinfo)(struct seq_file *m, int i);
+        /* Returns the current operating frequency of "cpu" in Hz */
+        unsigned long   (*get_proc_freq)(unsigned int cpu);
 
         void            (*init_IRQ)(void);
 
diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index 79b7612ac6fa..3cf25c89469d 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -212,6 +212,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 {
         unsigned long cpu_id = (unsigned long)v - 1;
         unsigned int pvr;
+        unsigned long proc_freq;
         unsigned short maj;
         unsigned short min;
 
@@ -263,12 +264,19 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 #endif /* CONFIG_TAU */
 
         /*
-         * Assume here that all clock rates are the same in a
-         * smp system.  -- Cort
+         * Platforms that have variable clock rates, should implement
+         * the method ppc_md.get_proc_freq() that reports the clock
+         * rate of a given cpu. The rest can use ppc_proc_freq to
+         * report the clock rate that is same across all cpus.
          */
-        if (ppc_proc_freq)
+        if (ppc_md.get_proc_freq)
+                proc_freq = ppc_md.get_proc_freq(cpu_id);
+        else
+                proc_freq = ppc_proc_freq;
+
+        if (proc_freq)
                 seq_printf(m, "clock\t\t: %lu.%06luMHz\n",
-                           ppc_proc_freq / 1000000, ppc_proc_freq % 1000000);
+                           proc_freq / 1000000, proc_freq % 1000000);
 
         if (ppc_md.show_percpuinfo != NULL)
                 ppc_md.show_percpuinfo(m, cpu_id);