ACPI/hpet: prevent boot hang when hpet=force used on ICH-4M

Linux tells ICH4 users that they can (manually) invoke
"hpet=force" to enable the undocumented ICH-4M HPET.
The HPET becomes available for both clocksource and clockevents.

But as of ff69f2bba67bd45514923aaedbf40fe351787c59
(acpi: fix of pmtimer overflow that make Cx states time incorrect)
the HPET may be used via clocksource for idle accounting, and
hpet=force on an ICH4 box hangs boot.

It turns out that touching the MMIO HPET withing
the ARB_DIS part of C3 will hang the hardware.

The fix is to simply move the timer access outside
the ARB_DIS region.  This is a no-op on modern hardware
because ARB_DIS is no longer used.

http://bugzilla.kernel.org/show_bug.cgi?id=13087

Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 6fe121434ffb36ec67a91b45823e3df3d45873c5..ea23c64bd766022277fab15add54c6e9b7901b77 100644 (file)
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -955,6 +955,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
         */
        acpi_state_timer_broadcast(pr, cx, 1);
 
+       kt1 = ktime_get_real();
        /*
         * disable bus master
         * bm_check implies we need ARB_DIS
@@ -976,10 +977,7 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
                ACPI_FLUSH_CPU_CACHE();
        }
 
-       kt1 = ktime_get_real();
        acpi_idle_do_entry(cx);
-       kt2 = ktime_get_real();
-       idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
 
        /* Re-enable bus master arbitration */
        if (pr->flags.bm_check && pr->flags.bm_control) {
@@ -988,6 +986,8 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
                c3_cpu_count--;
                spin_unlock(&c3_lock);
        }
+       kt2 = ktime_get_real();
+       idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
 
 #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
        /* TSC could halt in idle, so notify users */