[ACPI] Add a module parameter to allow tuning how much bus-master activity

we remember when entering C3 -- /sys/module/processor/parameters/bm_history
Default varies with HZ -- 40ms for 25 - 800 HZ, 32ms for 1000 HZ.
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/processor_idle.c

@@ -60,6 +60,15 @@ module_param(max_cstate, uint, 0644);
 static unsigned int nocst = 0;
 module_param(nocst, uint, 0000);
 
+/*
+ * bm_history -- bit-mask with a bit per jiffy of bus-master activity
+ * 1000 HZ: 0xFFFFFFFF: 32 jiffies = 32ms
+ * 800 HZ: 0xFFFFFFFF: 32 jiffies = 40ms
+ * 100 HZ: 0x0000000F: 4 jiffies = 40ms
+ * reduce history for more aggressive entry into C3
+ */
+static unsigned int bm_history = (HZ >= 800 ? 0xFFFFFFFF : ((1U << (HZ / 25)) - 1));
+module_param(bm_history, uint, 0644);
 /* --------------------------------------------------------------------------
                                 Power Management
    -------------------------------------------------------------------------- */
@@ -438,7 +447,7 @@ acpi_processor_set_power_policy (
 			cx->demotion.threshold.ticks = cx->latency_ticks;
 			cx->demotion.threshold.count = 1;
 			if (cx->type == ACPI_STATE_C3)
-				cx->demotion.threshold.bm = 0x0F;
+				cx->demotion.threshold.bm = bm_history;
 		}
 
 		lower = cx;
@@ -458,7 +467,7 @@ acpi_processor_set_power_policy (
 			else
 				cx->promotion.threshold.count = 10;
 			if (higher->type == ACPI_STATE_C3)
-				cx->promotion.threshold.bm = 0x0F;
+				cx->promotion.threshold.bm = bm_history;
 		}
 
 		higher = cx;