linux-kernel - [019/117] sfc: Wait at most 10ms for the MC to finish reading out MAC statistics

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Message-Id: <20100510223318.920040672@kvm.kroah.org>
Date:	Mon, 10 May 2010 15:31:50 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Ben Hutchings <bhutchings@...arflare.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [019/117] sfc: Wait at most 10ms for the MC to finish reading out MAC statistics

2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Ben Hutchings <bhutchings@...arflare.com>

commit aabc5649078310094cbffb430fcbf9c25b6268f9 upstream.

The original code would wait indefinitely if MAC stats DMA failed.

Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/net/sfc/siena.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/net/sfc/siena.c
+++ b/drivers/net/sfc/siena.c
@@ -454,8 +454,17 @@ static int siena_try_update_nic_stats(st
 
 static void siena_update_nic_stats(struct efx_nic *efx)
 {
-	while (siena_try_update_nic_stats(efx) == -EAGAIN)
-		cpu_relax();
+	int retry;
+
+	/* If we're unlucky enough to read statistics wduring the DMA, wait
+	 * up to 10ms for it to finish (typically takes <500us) */
+	for (retry = 0; retry < 100; ++retry) {
+		if (siena_try_update_nic_stats(efx) == 0)
+			return;
+		udelay(100);
+	}
+
+	/* Use the old values instead */
 }
 
 static void siena_start_nic_stats(struct efx_nic *efx)


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