sfc: Correct and expand some comments
These comments have been revised in response to questions raised by Andrew
Morton in <20080501120858.207b6dd6.akpm@linux-foundation.org>.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/net/sfc/efx.c b/drivers/net/sfc/efx.c
index f6131e5..11ee0d4 100644
--- a/drivers/net/sfc/efx.c
+++ b/drivers/net/sfc/efx.c
@@ -199,11 +199,12 @@
*/
static inline void efx_channel_processed(struct efx_channel *channel)
{
- /* Write to EVQ_RPTR_REG. If a new event arrived in a race
- * with finishing processing, a new interrupt will be raised.
- */
+ /* The interrupt handler for this channel may set work_pending
+ * as soon as we acknowledge the events we've seen. Make sure
+ * it's cleared before then. */
channel->work_pending = 0;
- smp_wmb(); /* Ensure channel updated before any new interrupt. */
+ smp_wmb();
+
falcon_eventq_read_ack(channel);
}
@@ -427,9 +428,12 @@
netif_napi_add(channel->napi_dev, &channel->napi_str,
efx_poll, napi_weight);
+ /* The interrupt handler for this channel may set work_pending
+ * as soon as we enable it. Make sure it's cleared before
+ * then. Similarly, make sure it sees the enabled flag set. */
channel->work_pending = 0;
channel->enabled = 1;
- smp_wmb(); /* ensure channel updated before first interrupt */
+ smp_wmb();
napi_enable(&channel->napi_str);
@@ -1332,13 +1336,17 @@
return 0;
}
-/* Context: process, dev_base_lock held, non-blocking. */
+/* Context: process, dev_base_lock or RTNL held, non-blocking. */
static struct net_device_stats *efx_net_stats(struct net_device *net_dev)
{
struct efx_nic *efx = net_dev->priv;
struct efx_mac_stats *mac_stats = &efx->mac_stats;
struct net_device_stats *stats = &net_dev->stats;
+ /* Update stats if possible, but do not wait if another thread
+ * is updating them (or resetting the NIC); slightly stale
+ * stats are acceptable.
+ */
if (!spin_trylock(&efx->stats_lock))
return stats;
if (efx->state == STATE_RUNNING) {