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authorRaanan Avargil <raanan.avargil@intel.com>2015-07-19 16:33:20 +0300
committerJeff Kirsher <jeffrey.t.kirsher@intel.com>2015-08-05 16:53:48 -0700
commit37b12910dd11d9ab969f2c310dc9160b7f3e3405 (patch)
tree153dfbbf9c83135c0e13fbeba8e62ab093b4d8b8 /drivers/net/ethernet/intel/e1000e
parent2758f9edb7bd5a06a2ecee83cc2ebaf8822a0cb5 (diff)
downloadlinux-linaro-stable-37b12910dd11d9ab969f2c310dc9160b7f3e3405.tar.gz
e1000e: Fix tight loop implementation of systime read algorithm
Change the algorithm. Read systimel twice and check for overflow. If there was no overflow, use the first value. If there was an overflow, read systimeh again and use the second systimel value. Signed-off-by: Raanan Avargil <raanan.avargil@intel.com> Tested-by: Aaron Brown <aaron.f.brown@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Diffstat (limited to 'drivers/net/ethernet/intel/e1000e')
-rw-r--r--drivers/net/ethernet/intel/e1000e/netdev.c31
1 files changed, 21 insertions, 10 deletions
diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
index 24b7269ff929..96a816683698 100644
--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
@@ -4280,18 +4280,29 @@ static cycle_t e1000e_cyclecounter_read(const struct cyclecounter *cc)
struct e1000_adapter *adapter = container_of(cc, struct e1000_adapter,
cc);
struct e1000_hw *hw = &adapter->hw;
+ u32 systimel_1, systimel_2, systimeh;
cycle_t systim, systim_next;
- /* SYSTIMH latching upon SYSTIML read does not work well. To fix that
- * we don't want to allow overflow of SYSTIML and a change to SYSTIMH
- * to occur between reads, so if we read a vale close to overflow, we
- * wait for overflow to occur and read both registers when its safe.
+ /* SYSTIMH latching upon SYSTIML read does not work well.
+ * This means that if SYSTIML overflows after we read it but before
+ * we read SYSTIMH, the value of SYSTIMH has been incremented and we
+ * will experience a huge non linear increment in the systime value
+ * to fix that we test for overflow and if true, we re-read systime.
*/
- u32 systim_overflow_latch_fix = 0x3FFFFFFF;
-
- do {
- systim = (cycle_t)er32(SYSTIML);
- } while (systim > systim_overflow_latch_fix);
- systim |= (cycle_t)er32(SYSTIMH) << 32;
+ systimel_1 = er32(SYSTIML);
+ systimeh = er32(SYSTIMH);
+ systimel_2 = er32(SYSTIML);
+ /* Check for overflow. If there was no overflow, use the values */
+ if (systimel_1 < systimel_2) {
+ systim = (cycle_t)systimel_1;
+ systim |= (cycle_t)systimeh << 32;
+ } else {
+ /* There was an overflow, read again SYSTIMH, and use
+ * systimel_2
+ */
+ systimeh = er32(SYSTIMH);
+ systim = (cycle_t)systimel_2;
+ systim |= (cycle_t)systimeh << 32;
+ }
if ((hw->mac.type == e1000_82574) || (hw->mac.type == e1000_82583)) {
u64 incvalue, time_delta, rem, temp;