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 (file)
--- 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;