[CPUFREQ] Measure transition latency at driver initialization

The attached patch introduces runtime latency measurement for ICH[234]
based chipsets instead of using CPUFREQ_ETERNAL. It includes
some sanity checks in case the measured value is out of range and
assigns a safe value of 500uSec that should still be enough on
problematics chipsets (current testing report values ~200uSec). The
measurement is currently done in speedstep_get_freqs in order to avoid
further unnecessary transitions and in the hope it'll come handy for SMI
also.

Signed-off-by: Mattia Dongili <malattia@linux.it>
Acked-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Dave Jones <davej@redhat.com>

 speedstep-ich.c |    4 ++--
 speedstep-lib.c |   32 +++++++++++++++++++++++++++++++-
 speedstep-lib.h |    1 +
 speedstep-smi.c |    1 +
 4 files changed, 35 insertions(+), 3 deletions(-)

4 files changed, 35 insertions, 3 deletions

diff --git a/arch/i386/kernel/cpu/cpufreq/speedstep-ich.c b/arch/i386/kernel/cpu/cpufreq/speedstep-ich.c
index 5b7d18a06af..862e0b5656b 100644
--- a/arch/i386/kernel/cpu/cpufreq/speedstep-ich.c
+++ b/arch/i386/kernel/cpu/cpufreq/speedstep-ich.c
@@ -315,10 +315,11 @@ static int speedstep_cpu_init(struct cpufreq_policy *policy)
         cpus_allowed = current->cpus_allowed;
         set_cpus_allowed(current, policy->cpus);
 
-        /* detect low and high frequency */
+        /* detect low and high frequency and transition latency */
         result = speedstep_get_freqs(speedstep_processor,
                                      &speedstep_freqs[SPEEDSTEP_LOW].frequency,
                                      &speedstep_freqs[SPEEDSTEP_HIGH].frequency,
+                                     &policy->cpuinfo.transition_latency,
                                      &speedstep_set_state);
         set_cpus_allowed(current, cpus_allowed);
         if (result)
@@ -335,7 +336,6 @@ static int speedstep_cpu_init(struct cpufreq_policy *policy)
 
         /* cpuinfo and default policy values */
         policy->governor = CPUFREQ_DEFAULT_GOVERNOR;
-        policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
         policy->cur = speed;
 
         result = cpufreq_frequency_table_cpuinfo(policy, speedstep_freqs);
diff --git a/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c b/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c
index d368b3f5fce..7c47005a180 100644
--- a/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c
+++ b/arch/i386/kernel/cpu/cpufreq/speedstep-lib.c
@@ -320,11 +320,13 @@ EXPORT_SYMBOL_GPL(speedstep_detect_processor);
 unsigned int speedstep_get_freqs(unsigned int processor,
                                   unsigned int *low_speed,
                                   unsigned int *high_speed,
+                                  unsigned int *transition_latency,
                                   void (*set_state) (unsigned int state))
 {
         unsigned int prev_speed;
         unsigned int ret = 0;
         unsigned long flags;
+        struct timeval tv1, tv2;
 
         if ((!processor) || (!low_speed) || (!high_speed) || (!set_state))
                 return -EINVAL;
@@ -337,7 +339,7 @@ unsigned int speedstep_get_freqs(unsigned int processor,
                 return -EIO;
 
         dprintk("previous speed is %u\n", prev_speed);
-        
+
         local_irq_save(flags);
 
         /* switch to low state */
@@ -350,8 +352,17 @@ unsigned int speedstep_get_freqs(unsigned int processor,
 
         dprintk("low speed is %u\n", *low_speed);
 
+        /* start latency measurement */
+        if (transition_latency)
+                do_gettimeofday(&tv1);
+
         /* switch to high state */
         set_state(SPEEDSTEP_HIGH);
+
+        /* end latency measurement */
+        if (transition_latency)
+                do_gettimeofday(&tv2);
+
         *high_speed = speedstep_get_processor_frequency(processor);
         if (!*high_speed) {
                 ret = -EIO;
@@ -369,6 +380,25 @@ unsigned int speedstep_get_freqs(unsigned int processor,
         if (*high_speed != prev_speed)
                 set_state(SPEEDSTEP_LOW);
 
+        if (transition_latency) {
+                *transition_latency = (tv2.tv_sec - tv1.tv_sec) * USEC_PER_SEC +
+                        tv2.tv_usec - tv1.tv_usec;
+                dprintk("transition latency is %u uSec\n", *transition_latency);
+
+                /* convert uSec to nSec and add 20% for safety reasons */
+                *transition_latency *= 1200;
+
+                /* check if the latency measurement is too high or too low
+                 * and set it to a safe value (500uSec) in that case
+                 */
+                if (*transition_latency > 10000000 || *transition_latency < 50000) {
+                        printk (KERN_WARNING "speedstep: frequency transition measured seems out of "
+                                        "range (%u nSec), falling back to a safe one of %u nSec.\n",
+                                        *transition_latency, 500000);
+                        *transition_latency = 500000;
+                }
+        }
+
  out:
         local_irq_restore(flags);
         return (ret);
diff --git a/arch/i386/kernel/cpu/cpufreq/speedstep-lib.h b/arch/i386/kernel/cpu/cpufreq/speedstep-lib.h
index 261a2c9b7f6..6a727fd3a77 100644
--- a/arch/i386/kernel/cpu/cpufreq/speedstep-lib.h
+++ b/arch/i386/kernel/cpu/cpufreq/speedstep-lib.h
@@ -44,4 +44,5 @@ extern unsigned int speedstep_get_processor_frequency(unsigned int processor);
 extern unsigned int speedstep_get_freqs(unsigned int processor,
           unsigned int *low_speed,
           unsigned int *high_speed,
+          unsigned int *transition_latency,
           void (*set_state) (unsigned int state));
diff --git a/arch/i386/kernel/cpu/cpufreq/speedstep-smi.c b/arch/i386/kernel/cpu/cpufreq/speedstep-smi.c
index 2718fb6f6ab..28cc5d524af 100644
--- a/arch/i386/kernel/cpu/cpufreq/speedstep-smi.c
+++ b/arch/i386/kernel/cpu/cpufreq/speedstep-smi.c
@@ -269,6 +269,7 @@ static int speedstep_cpu_init(struct cpufreq_policy *policy)
                 result = speedstep_get_freqs(speedstep_processor,
                                 &speedstep_freqs[SPEEDSTEP_LOW].frequency,
                                 &speedstep_freqs[SPEEDSTEP_HIGH].frequency,
+                                NULL,
                                 &speedstep_set_state);
 
                 if (result) {