[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(-)

1 files changed, 31 insertions, 1 deletions

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);