hpet: fix the possibility of insane return value of hpet_calibrate() against SMI
hpet_calibrate() has a possibility of miss-calibration due to SMI. If SMI
interrupts in the while loop of calibration, then return value will be
big. This change calibrates until stabilizing by the return value with a
small value.
[akpm@linux-foundation.org: trivial style tweaks]
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Acked-by: Vojtech Pavlik <vojtech@suse.cz>
Cc: Robert Picco <Robert.Picco@hp.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 32b8bbf..50dfa3b 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -713,7 +713,7 @@
*/
#define TICK_CALIBRATE (1000UL)
-static unsigned long hpet_calibrate(struct hpets *hpetp)
+static unsigned long __hpet_calibrate(struct hpets *hpetp)
{
struct hpet_timer __iomem *timer = NULL;
unsigned long t, m, count, i, flags, start;
@@ -750,6 +750,26 @@
return (m - start) / i;
}
+static unsigned long hpet_calibrate(struct hpets *hpetp)
+{
+ unsigned long ret = -1;
+ unsigned long tmp;
+
+ /*
+ * Try to calibrate until return value becomes stable small value.
+ * If SMI interruption occurs in calibration loop, the return value
+ * will be big. This avoids its impact.
+ */
+ for ( ; ; ) {
+ tmp = __hpet_calibrate(hpetp);
+ if (ret <= tmp)
+ break;
+ ret = tmp;
+ }
+
+ return ret;
+}
+
int hpet_alloc(struct hpet_data *hdp)
{
u64 cap, mcfg;