forked from AUR/linux-vfio
66 lines
2.6 KiB
Diff
66 lines
2.6 KiB
Diff
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From 37b12910dd11d9ab969f2c310dc9160b7f3e3405 Mon Sep 17 00:00:00 2001
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From: Raanan Avargil <raanan.avargil@intel.com>
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Date: Sun, 19 Jul 2015 16:33:20 +0300
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Subject: [PATCH] e1000e: Fix tight loop implementation of systime read
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algorithm
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Change the algorithm. Read systimel twice and check for overflow.
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If there was no overflow, use the first value.
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If there was an overflow, read systimeh again and use the second
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systimel value.
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Signed-off-by: Raanan Avargil <raanan.avargil@intel.com>
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Tested-by: Aaron Brown <aaron.f.brown@intel.com>
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Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
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---
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drivers/net/ethernet/intel/e1000e/netdev.c | 31 ++++++++++++++++++++----------
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1 file changed, 21 insertions(+), 10 deletions(-)
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diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
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index 24b7269..96a8166 100644
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--- a/drivers/net/ethernet/intel/e1000e/netdev.c
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+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
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@@ -4280,18 +4280,29 @@ static cycle_t e1000e_cyclecounter_read(const struct cyclecounter *cc)
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struct e1000_adapter *adapter = container_of(cc, struct e1000_adapter,
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cc);
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struct e1000_hw *hw = &adapter->hw;
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+ u32 systimel_1, systimel_2, systimeh;
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cycle_t systim, systim_next;
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- /* SYSTIMH latching upon SYSTIML read does not work well. To fix that
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- * we don't want to allow overflow of SYSTIML and a change to SYSTIMH
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- * to occur between reads, so if we read a vale close to overflow, we
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- * wait for overflow to occur and read both registers when its safe.
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+ /* SYSTIMH latching upon SYSTIML read does not work well.
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+ * This means that if SYSTIML overflows after we read it but before
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+ * we read SYSTIMH, the value of SYSTIMH has been incremented and we
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+ * will experience a huge non linear increment in the systime value
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+ * to fix that we test for overflow and if true, we re-read systime.
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*/
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- u32 systim_overflow_latch_fix = 0x3FFFFFFF;
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-
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- do {
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- systim = (cycle_t)er32(SYSTIML);
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- } while (systim > systim_overflow_latch_fix);
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- systim |= (cycle_t)er32(SYSTIMH) << 32;
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+ systimel_1 = er32(SYSTIML);
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+ systimeh = er32(SYSTIMH);
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+ systimel_2 = er32(SYSTIML);
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+ /* Check for overflow. If there was no overflow, use the values */
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+ if (systimel_1 < systimel_2) {
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+ systim = (cycle_t)systimel_1;
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+ systim |= (cycle_t)systimeh << 32;
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+ } else {
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+ /* There was an overflow, read again SYSTIMH, and use
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+ * systimel_2
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+ */
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+ systimeh = er32(SYSTIMH);
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+ systim = (cycle_t)systimel_2;
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+ systim |= (cycle_t)systimeh << 32;
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+ }
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if ((hw->mac.type == e1000_82574) || (hw->mac.type == e1000_82583)) {
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u64 incvalue, time_delta, rem, temp;
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--
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2.5.1
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