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

[Greg KH]

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

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

From: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>

commit aabc5649078310094cbffb430fcbf9c25b6268f9 upstream.

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

Signed-off-by: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 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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