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e1000e: e1000e_cyclecounter_read(): fix er32(SYSTIML) overflow check 

If two consecutive reads of the counter are the same, it is also
not an overflow.  "systimel_1 < systimel_2" should be
"systimel_1 <= systimel_2".

Before the patch, we could perform an *erroneous* correction:

Let's say that systimel_1 == systimel_2 == 0xffffffff.
"systimel_1 < systimel_2" is false, we think it's an overflow,
we read "systimeh = er32(SYSTIMH)" which meanwhile had incremented,
and use "(systimeh << 32) + systimel_2" value which is 2^32 too large.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: intel-wired-lan@lists.osuosl.org
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
This commit is contained in:
Denys Vlasenko 2016-04-20 17:45:55 +02:00 committed by Jeff Kirsher
parent fb5277f2c2
commit a07fd74d5e
1 changed files with 1 additions and 1 deletions
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2
drivers/net/ethernet/intel/e1000e/netdev.c
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@ -4287,7 +4287,7 @@ static cycle_t e1000e_cyclecounter_read(const struct cyclecounter *cc)
systimeh = er32(SYSTIMH);
systimel_2 = er32(SYSTIML);
/* Check for overflow. If there was no overflow, use the values */
if (systimel_1 < systimel_2) {
if (systimel_1 <= systimel_2) {
systim = (cycle_t)systimel_1;
systim |= (cycle_t)systimeh << 32;
} else {