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Subject[PATCH v6 3/7] igbvf: eliminate duplicate barriers on weakly-ordered archs
Date
Code includes wmb() followed by writel(). writel() already has a barrier
on some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Since code already has an explicit barrier call, changing writel() to
writel_relaxed().

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
---
drivers/net/ethernet/intel/igbvf/netdev.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/igbvf/netdev.c b/drivers/net/ethernet/intel/igbvf/netdev.c
index fa07876..6dfd3dc 100644
--- a/drivers/net/ethernet/intel/igbvf/netdev.c
+++ b/drivers/net/ethernet/intel/igbvf/netdev.c
@@ -252,7 +252,12 @@ static void igbvf_alloc_rx_buffers(struct igbvf_ring *rx_ring,
* such as IA-64).
*/
wmb();
- writel(i, adapter->hw.hw_addr + rx_ring->tail);
+ writel_relaxed(i, adapter->hw.hw_addr + rx_ring->tail);
+
+ /* We need this if more than one processor can write to our tail
+ * at a time, it synchronizes IO on IA64/Altix systems
+ */
+ mmiowb();
}
}

@@ -2298,7 +2303,7 @@ static inline void igbvf_tx_queue_adv(struct igbvf_adapter *adapter,

tx_ring->buffer_info[first].next_to_watch = tx_desc;
tx_ring->next_to_use = i;
- writel(i, adapter->hw.hw_addr + tx_ring->tail);
+ writel_relaxed(i, adapter->hw.hw_addr + tx_ring->tail);
/* we need this if more than one processor can write to our tail
* at a time, it synchronizes IO on IA64/Altix systems
*/
--
2.7.4
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