sfc: Replace stats_enabled flag with a disable count

Currently we use a spin-lock to serialise statistics fetches and also
to inhibit them for short periods of time, plus a flag to
enable/disable statistics fetches for longer periods of time, during
online reset.  This was apparently insufficient to deal with the several
reasons for stats being disabled.

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

6 files changed, 57 insertions, 25 deletions

diff --git a/drivers/net/sfc/efx.c b/drivers/net/sfc/efx.c
index b0e53087bda0..ab0e09bf154d 100644
--- a/drivers/net/sfc/efx.c
+++ b/drivers/net/sfc/efx.c
@@ -685,7 +685,7 @@ static int efx_init_port(struct efx_nic *efx)
         efx->mac_op->reconfigure(efx);
 
         efx->port_initialized = true;
-        efx->stats_enabled = true;
+        efx_stats_enable(efx);
         return 0;
 
 fail:
@@ -734,6 +734,7 @@ static void efx_fini_port(struct efx_nic *efx)
         if (!efx->port_initialized)
                 return;
 
+        efx_stats_disable(efx);
         efx->phy_op->fini(efx);
         efx->port_initialized = false;
 
@@ -1360,6 +1361,20 @@ static int efx_net_stop(struct net_device *net_dev)
         return 0;
 }
 
+void efx_stats_disable(struct efx_nic *efx)
+{
+        spin_lock(&efx->stats_lock);
+        ++efx->stats_disable_count;
+        spin_unlock(&efx->stats_lock);
+}
+
+void efx_stats_enable(struct efx_nic *efx)
+{
+        spin_lock(&efx->stats_lock);
+        --efx->stats_disable_count;
+        spin_unlock(&efx->stats_lock);
+}
+
 /* Context: process, dev_base_lock or RTNL held, non-blocking. */
 static struct net_device_stats *efx_net_stats(struct net_device *net_dev)
 {
@@ -1368,12 +1383,12 @@ static struct net_device_stats *efx_net_stats(struct net_device *net_dev)
         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.
+         * is updating them or if MAC stats fetches are temporarily
+         * disabled; slightly stale stats are acceptable.
          */
         if (!spin_trylock(&efx->stats_lock))
                 return stats;
-        if (efx->stats_enabled) {
+        if (!efx->stats_disable_count) {
                 efx->mac_op->update_stats(efx);
                 falcon_update_nic_stats(efx);
         }
@@ -1626,12 +1641,7 @@ void efx_reset_down(struct efx_nic *efx, enum reset_type method,
 {
         EFX_ASSERT_RESET_SERIALISED(efx);
 
-        /* The net_dev->get_stats handler is quite slow, and will fail
-         * if a fetch is pending over reset. Serialise against it. */
-        spin_lock(&efx->stats_lock);
-        efx->stats_enabled = false;
-        spin_unlock(&efx->stats_lock);
-
+        efx_stats_disable(efx);
         efx_stop_all(efx);
         mutex_lock(&efx->mac_lock);
         mutex_lock(&efx->spi_lock);
@@ -1682,7 +1692,7 @@ int efx_reset_up(struct efx_nic *efx, enum reset_type method,
 
         if (ok) {
                 efx_start_all(efx);
-                efx->stats_enabled = true;
+                efx_stats_enable(efx);
         }
         return rc;
 }
@@ -1888,6 +1898,7 @@ static int efx_init_struct(struct efx_nic *efx, struct efx_nic_type *type,
         efx->rx_checksum_enabled = true;
         spin_lock_init(&efx->netif_stop_lock);
         spin_lock_init(&efx->stats_lock);
+        efx->stats_disable_count = 1;
         mutex_init(&efx->mac_lock);
         efx->mac_op = &efx_dummy_mac_operations;
         efx->phy_op = &efx_dummy_phy_operations;
diff --git a/drivers/net/sfc/efx.h b/drivers/net/sfc/efx.h
index ac201587a163..55d0f131b0e9 100644
--- a/drivers/net/sfc/efx.h
+++ b/drivers/net/sfc/efx.h
@@ -36,6 +36,8 @@ extern void efx_process_channel_now(struct efx_channel *channel);
 extern void efx_flush_queues(struct efx_nic *efx);
 
 /* Ports */
+extern void efx_stats_disable(struct efx_nic *efx);
+extern void efx_stats_enable(struct efx_nic *efx);
 extern void efx_reconfigure_port(struct efx_nic *efx);
 extern void __efx_reconfigure_port(struct efx_nic *efx);
 
diff --git a/drivers/net/sfc/falcon.c b/drivers/net/sfc/falcon.c
index d9412f83a78e..d5378e60fcdd 100644
--- a/drivers/net/sfc/falcon.c
+++ b/drivers/net/sfc/falcon.c
@@ -1883,7 +1883,7 @@ static int falcon_reset_macs(struct efx_nic *efx)
 
         /* MAC stats will fail whilst the TX fifo is draining. Serialise
          * the drain sequence with the statistics fetch */
-        spin_lock(&efx->stats_lock);
+        efx_stats_disable(efx);
 
         falcon_read(efx, &reg, MAC0_CTRL_REG_KER);
         EFX_SET_OWORD_FIELD(reg, TXFIFO_DRAIN_EN_B0, 1);
@@ -1913,7 +1913,7 @@ static int falcon_reset_macs(struct efx_nic *efx)
                 udelay(10);
         }
 
-        spin_unlock(&efx->stats_lock);
+        efx_stats_enable(efx);
 
         /* If we've reset the EM block and the link is up, then
          * we'll have to kick the XAUI link so the PHY can recover */
@@ -2273,6 +2273,10 @@ int falcon_switch_mac(struct efx_nic *efx)
         struct efx_mac_operations *old_mac_op = efx->mac_op;
         efx_oword_t nic_stat;
         unsigned strap_val;
+        int rc = 0;
+
+        /* Don't try to fetch MAC stats while we're switching MACs */
+        efx_stats_disable(efx);
 
         /* Internal loopbacks override the phy speed setting */
         if (efx->loopback_mode == LOOPBACK_GMAC) {
@@ -2302,13 +2306,16 @@ int falcon_switch_mac(struct efx_nic *efx)
         }
 
         if (old_mac_op == efx->mac_op)
-                return 0;
+                goto out;
 
         EFX_LOG(efx, "selected %cMAC\n", EFX_IS10G(efx) ? 'X' : 'G');
         /* Not all macs support a mac-level link state */
         efx->mac_up = true;
 
-        return falcon_reset_macs(efx);
+        rc = falcon_reset_macs(efx);
+out:
+        efx_stats_enable(efx);
+        return rc;
 }
 
 /* This call is responsible for hooking in the MAC and PHY operations */
diff --git a/drivers/net/sfc/net_driver.h b/drivers/net/sfc/net_driver.h
index 8eb411a1c82e..e019ad1fb9a0 100644
--- a/drivers/net/sfc/net_driver.h
+++ b/drivers/net/sfc/net_driver.h
@@ -754,8 +754,7 @@ union efx_multicast_hash {
  *      &struct net_device_stats.