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From: Finn Thain <fthain@telegraphics.com.au>
To: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Chris Zankel <chris@zankel.net>,
	Laurent Vivier <laurent@vivier.eu>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH net v3 06/12] net/sonic: Avoid needless receive descriptor EOL flag updates
Date: Thu, 23 Jan 2020 09:07:26 +1100	[thread overview]
Message-ID: <36024a80d3f0428430752ce1428b7dc3e6f19f9e.1579730846.git.fthain@telegraphics.com.au> (raw)
In-Reply-To: <cover.1579730846.git.fthain@telegraphics.com.au>

The while loop in sonic_rx() traverses the rx descriptor ring. It stops
when it reaches a descriptor that the SONIC has not used. Each iteration
advances the EOL flag so the SONIC can keep using more descriptors.
Therefore, the while loop has no definite termination condition.

The algorithm described in the National Semiconductor literature is quite
different. It consumes descriptors up to the one with its EOL flag set
(which will also have its "in use" flag set). All freed descriptors are
then returned to the ring at once, by adjusting the EOL flags (and link
pointers).

Adopt the algorithm from datasheet as it's simpler, terminates quickly
and avoids a lot of pointless descriptor EOL flag changes.

Fixes: efcce839360f ("[PATCH] macsonic/jazzsonic network drivers update")
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
---
 drivers/net/ethernet/natsemi/sonic.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/natsemi/sonic.c b/drivers/net/ethernet/natsemi/sonic.c
index c666bbf15116..2cee702f49b8 100644
--- a/drivers/net/ethernet/natsemi/sonic.c
+++ b/drivers/net/ethernet/natsemi/sonic.c
@@ -436,6 +436,7 @@ static void sonic_rx(struct net_device *dev)
 	struct sonic_local *lp = netdev_priv(dev);
 	int status;
 	int entry = lp->cur_rx;
+	int prev_entry = lp->eol_rx;
 
 	while (sonic_rda_get(dev, entry, SONIC_RD_IN_USE) == 0) {
 		struct sk_buff *used_skb;
@@ -516,13 +517,21 @@ static void sonic_rx(struct net_device *dev)
 		/*
 		 * give back the descriptor
 		 */
-		sonic_rda_put(dev, entry, SONIC_RD_LINK,
-			sonic_rda_get(dev, entry, SONIC_RD_LINK) | SONIC_EOL);
 		sonic_rda_put(dev, entry, SONIC_RD_IN_USE, 1);
-		sonic_rda_put(dev, lp->eol_rx, SONIC_RD_LINK,
-			sonic_rda_get(dev, lp->eol_rx, SONIC_RD_LINK) & ~SONIC_EOL);
-		lp->eol_rx = entry;
-		lp->cur_rx = entry = (entry + 1) & SONIC_RDS_MASK;
+
+		prev_entry = entry;
+		entry = (entry + 1) & SONIC_RDS_MASK;
+	}
+
+	lp->cur_rx = entry;
+
+	if (prev_entry != lp->eol_rx) {
+		/* Advance the EOL flag to put descriptors back into service */
+		sonic_rda_put(dev, prev_entry, SONIC_RD_LINK, SONIC_EOL |
+			      sonic_rda_get(dev, prev_entry, SONIC_RD_LINK));
+		sonic_rda_put(dev, lp->eol_rx, SONIC_RD_LINK, ~SONIC_EOL &
+			      sonic_rda_get(dev, lp->eol_rx, SONIC_RD_LINK));
+		lp->eol_rx = prev_entry;
 	}
 	/*
 	 * If any worth-while packets have been received, netif_rx()
-- 
2.24.1


  parent reply	other threads:[~2020-01-22 22:24 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-22 22:07 [PATCH net v3 00/12] Fixes for SONIC ethernet driver Finn Thain
2020-01-22 22:07 ` [PATCH net v3 10/12] net/sonic: Fix command register usage Finn Thain
2020-01-22 22:07 ` [PATCH net v3 04/12] net/sonic: Fix interface error stats collection Finn Thain
2020-01-22 22:07 ` [PATCH net v3 08/12] net/sonic: Fix receive buffer replenishment Finn Thain
2020-01-22 22:07 ` [PATCH net v3 02/12] net/sonic: Clear interrupt flags immediately Finn Thain
2020-01-22 22:07 ` Finn Thain [this message]
2020-01-22 22:07 ` [PATCH net v3 03/12] net/sonic: Use MMIO accessors Finn Thain
2020-01-22 22:07 ` [PATCH net v3 11/12] net/sonic: Fix CAM initialization Finn Thain
2020-01-22 22:07 ` [PATCH net v3 12/12] net/sonic: Prevent tx watchdog timeout Finn Thain
2020-01-22 22:07 ` [PATCH net v3 09/12] net/sonic: Quiesce SONIC before re-initializing descriptor memory Finn Thain
2020-01-22 22:07 ` [PATCH net v3 07/12] net/sonic: Improve receive descriptor status flag check Finn Thain
2020-01-22 22:07 ` [PATCH net v3 01/12] net/sonic: Add mutual exclusion for accessing shared state Finn Thain
2020-01-22 22:07 ` [PATCH net v3 05/12] net/sonic: Fix receive buffer handling Finn Thain
2020-01-23 20:24 ` [PATCH net v3 00/12] Fixes for SONIC ethernet driver David Miller

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