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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>
This commit is contained in:
Yasunori Goto 2009-04-02 16:58:31 -07:00 committed by Linus Torvalds
parent 1f80769ffd
commit 303d379c54
1 changed files with 21 additions and 1 deletions
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22
drivers/char/hpet.c
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@ -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;