netdev - [PATCH v8 5/7] fm10k: Eliminate duplicate barriers on weakly-ordered archs

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Message-Id: <1522695990-31082-6-git-send-email-okaya@codeaurora.org>
Date:   Mon,  2 Apr 2018 15:06:28 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     jeffrey.t.kirsher@...el.com
Cc:     netdev@...r.kernel.org, timur@...eaurora.org,
        sulrich@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        intel-wired-lan@...ts.osuosl.org, linux-kernel@...r.kernel.org
Subject: [PATCH v8 5/7] fm10k: Eliminate duplicate barriers on weakly-ordered archs

memory-barriers.txt has been updated as follows:

"When using writel(), a prior wmb() is not needed to guarantee that the
cache coherent memory writes have completed before writing to the MMIO
region."

Remove old IA-64 comments in the code along with unneeded wmb() in front
of writel().

There are places in the code where wmb() has been used as a double barrier
for CPU and IO in place of smp_wmb() and wmb() as an optimization. For
such places, keep the wmb() but replace the following writel() with
writel_relaxed() to have a sequence as

wmb()
writel_relaxed()
mmio_wb()

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/net/ethernet/intel/fm10k/fm10k_main.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/drivers/net/ethernet/intel/fm10k/fm10k_main.c b/drivers/net/ethernet/intel/fm10k/fm10k_main.c
index df86070..41e3aaa 100644
--- a/drivers/net/ethernet/intel/fm10k/fm10k_main.c
+++ b/drivers/net/ethernet/intel/fm10k/fm10k_main.c
@@ -172,13 +172,6 @@ void fm10k_alloc_rx_buffers(struct fm10k_ring *rx_ring, u16 cleaned_count)
 		/* update next to alloc since we have filled the ring */
 		rx_ring->next_to_alloc = i;
 
-		/* Force memory writes to complete before letting h/w
-		 * know there are new descriptors to fetch.  (Only
-		 * applicable for weak-ordered memory model archs,
-		 * such as IA-64).
-		 */
-		wmb();
-
 		/* notify hardware of new descriptors */
 		writel(i, rx_ring->tail);
 	}
@@ -1036,11 +1029,7 @@ static void fm10k_tx_map(struct fm10k_ring *tx_ring,
 	/* record SW timestamp if HW timestamp is not available */
 	skb_tx_timestamp(first->skb);
 
-	/* Force memory writes to complete before letting h/w know there
-	 * are new descriptors to fetch.  (Only applicable for weak-ordered
-	 * memory model archs, such as IA-64).
-	 *
-	 * We also need this memory barrier to make certain all of the
+	/* We need this memory barrier to make certain all of the
 	 * status bits have been updated before next_to_watch is written.
 	 */
 	wmb();
@@ -1055,7 +1044,7 @@ static void fm10k_tx_map(struct fm10k_ring *tx_ring,
 
 	/* notify HW of packet */
 	if (netif_xmit_stopped(txring_txq(tx_ring)) || !skb->xmit_more) {
-		writel(i, tx_ring->tail);
+		writel_relaxed(i, 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