1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
index 05209b5cc6ca..19f6b9d27e83 100644
--- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
+++ b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c
@@ -682,6 +682,18 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
                             perf->states[i].transition_latency * 1000;
         }
 
+        /* Check for high latency (>20uS) from buggy BIOSes, like on T42 */
+        if (perf->control_register.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE &&
+            policy->cpuinfo.transition_latency > 20 * 1000) {
+                static int print_once;
+                policy->cpuinfo.transition_latency = 20 * 1000;
+                if (!print_once) {
+                        print_once = 1;
+                        printk(KERN_INFO "Capping off P-state tranision latency"
+                                " at 20 uS\n");
+                }
+        }
+
         data->max_freq = perf->states[0].core_frequency * 1000;
         /* table init */
         for (i = 0; i < perf->state_count; i++) {