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 d368b3f5fce8..7c47005a1805 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);