[RFC PATCH 1/2] powerpc: powernv: Framework to show the correct clock in /proc/cpuinfo

["Gautham R. Shenoy" <ego@linux.vnet.ibm.com>]

From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

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>
---
 arch/powerpc/include/asm/machdep.h |  2 ++
 arch/powerpc/kernel/setup-common.c | 16 ++++++++++++----
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
index ad3025d..eb1c6d4 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 bc76cc6..bdd3045 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -209,6 +209,7 @@ 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;
 
@@ -260,12 +261,19 @@ 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);
-- 
1.8.3.1