sfc: Wait at most 10ms for the MC to finish reading out MAC statistics

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

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Cc: stable@kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 2 deletions

diff --git a/drivers/net/sfc/siena.c b/drivers/net/sfc/siena.c
index 38dcc42c4f79..e0c46f59d1f8 100644
--- a/drivers/net/sfc/siena.c
+++ b/drivers/net/sfc/siena.c
@@ -456,8 +456,17 @@ static int siena_try_update_nic_stats(struct efx_nic *efx)
 
 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)