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>

1 files changed, 21 insertions, 1 deletions

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 32b8bbf5003e..50dfa3bc71ce 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -713,7 +713,7 @@ static struct ctl_table_header *sysctl_header;
  */
 #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 @@ static unsigned long hpet_calibrate(struct hpets *hpetp)
         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;