[CPUFREQ] allow ondemand and conservative cpufreq governors to be used as default

Depending on the transition latency of the HW for cpufreq switches, the
ondemand or conservative governor cannot be used with certain cpufreq
drivers.  Still the ondemand should be the default governor on a wide range
of systems.  This patch allows this and lets the governor fallback to the
performance governor at cpufreq driver load time, if the driver does not
support fast enough frequency switching.

Main benefit is that on e.g.  installation or other systems without
userspace support a working dynamic cpufreq support can be achieved on most
systems by simply loading the cpufreq driver.  This is especially essential
for recent x86(_64) laptop hardware which may rely on working dynamic
cpufreq OS support.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Bryan Wu <bryan.wu@analog.com>
Cc: Andi Kleen <ak@suse.de>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 17 insertions, 3 deletions

diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 3ec6e7ff5fbd..9e5f5d0c87f3 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -155,6 +155,9 @@ struct cpufreq_governor {
         char    name[CPUFREQ_NAME_LEN];
         int     (*governor)     (struct cpufreq_policy *policy,
                                  unsigned int event);
+        unsigned int max_transition_latency; /* HW must be able to switch to
+                        next freq faster than this value in nano secs or we
+                        will fallback to performance governor */
         struct list_head        governor_list;
         struct module           *owner;
 };
@@ -279,12 +282,23 @@ static inline unsigned int cpufreq_quick_get(unsigned int cpu)
  *********************************************************************/
 
 
-#ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE
+/*
+  Performance governor is fallback governor if any other gov failed to
+  auto load due latency restrictions
+*/
 extern struct cpufreq_governor cpufreq_gov_performance;
-#define CPUFREQ_DEFAULT_GOVERNOR        &cpufreq_gov_performance
+#define CPUFREQ_PERFORMANCE_GOVERNOR    (&cpufreq_gov_performance)
+#ifdef CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE
+#define CPUFREQ_DEFAULT_GOVERNOR        (&cpufreq_gov_performance)
 #elif defined(CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE)
 extern struct cpufreq_governor cpufreq_gov_userspace;
-#define CPUFREQ_DEFAULT_GOVERNOR        &cpufreq_gov_userspace
+#define CPUFREQ_DEFAULT_GOVERNOR        (&cpufreq_gov_userspace)
+#elif defined(CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND)
+extern struct cpufreq_governor cpufreq_gov_ondemand;
+#define CPUFREQ_DEFAULT_GOVERNOR        (&cpufreq_gov_ondemand)
+#elif defined(CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE)
+extern struct cpufreq_governor cpufreq_gov_conservative;
+#define CPUFREQ_DEFAULT_GOVERNOR        (&cpufreq_gov_conservative)
 #endif