[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(-)

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);

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;
@@ -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);

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));

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) {