TI DaVinci EMAC: Clear statistics register properly.

The mechanism to clear the statistics register is dependent
on the status of GMIIEN bit in MAC control register. If the
GMIIEN bit is set, the stats registers are write to decrement.
If the GMIIEN bit is cleared, the stats registers are plain
read/write registers. The stats register clearing operation
must take into account the current state of GMIIEN as it
can be cleared when the interface is brought down.

With existing implementation logic, querying for interface stats
when the interface is down, can corrupt the statistics counters.
This patch examines the GMIIEN bit status in MAC_CONTROL
register before choosing an appropriate mask for clearing stats
registers.
Signed-off-by: Sriramakrishnan <srk@ti.com>
Acked-by: Chaithrika U S <chaithrika@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/davinci_emac.c

@@ -333,6 +333,9 @@ static const char emac_version_string[] = "TI DaVinci EMAC Linux v6.1";
 #define EMAC_DM646X_MAC_EOI_C0_RXEN	(0x01)
 #define EMAC_DM646X_MAC_EOI_C0_TXEN	(0x02)
 
+/* EMAC Stats Clear Mask */
+#define EMAC_STATS_CLR_MASK    (0xFFFFFFFF)
+
 /** net_buf_obj: EMAC network bufferdata structure
  *
  * EMAC network buffer data structure
@@ -2548,40 +2551,49 @@ static int emac_dev_stop(struct net_device *ndev)
 static struct net_device_stats *emac_dev_getnetstats(struct net_device *ndev)
 {
 	struct emac_priv *priv = netdev_priv(ndev);
+	u32 mac_control;
+	u32 stats_clear_mask;
 
 	/* update emac hardware stats and reset the registers*/
 
+	mac_control = emac_read(EMAC_MACCONTROL);
+
+	if (mac_control & EMAC_MACCONTROL_GMIIEN)
+		stats_clear_mask = EMAC_STATS_CLR_MASK;
+	else
+		stats_clear_mask = 0;
+
 	priv->net_dev_stats.multicast += emac_read(EMAC_RXMCASTFRAMES);
-	emac_write(EMAC_RXMCASTFRAMES, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_RXMCASTFRAMES, stats_clear_mask);
 
 	priv->net_dev_stats.collisions += (emac_read(EMAC_TXCOLLISION) +
 					   emac_read(EMAC_TXSINGLECOLL) +
 					   emac_read(EMAC_TXMULTICOLL));
-	emac_write(EMAC_TXCOLLISION, EMAC_ALL_MULTI_REG_VALUE);
-	emac_write(EMAC_TXSINGLECOLL, EMAC_ALL_MULTI_REG_VALUE);
-	emac_write(EMAC_TXMULTICOLL, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_TXCOLLISION, stats_clear_mask);
+	emac_write(EMAC_TXSINGLECOLL, stats_clear_mask);
+	emac_write(EMAC_TXMULTICOLL, stats_clear_mask);
 
 	priv->net_dev_stats.rx_length_errors += (emac_read(EMAC_RXOVERSIZED) +
 						emac_read(EMAC_RXJABBER) +
 						emac_read(EMAC_RXUNDERSIZED));
-	emac_write(EMAC_RXOVERSIZED, EMAC_ALL_MULTI_REG_VALUE);
-	emac_write(EMAC_RXJABBER, EMAC_ALL_MULTI_REG_VALUE);
-	emac_write(EMAC_RXUNDERSIZED, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_RXOVERSIZED, stats_clear_mask);
+	emac_write(EMAC_RXJABBER, stats_clear_mask);
+	emac_write(EMAC_RXUNDERSIZED, stats_clear_mask);
 
 	priv->net_dev_stats.rx_over_errors += (emac_read(EMAC_RXSOFOVERRUNS) +
 					       emac_read(EMAC_RXMOFOVERRUNS));
-	emac_write(EMAC_RXSOFOVERRUNS, EMAC_ALL_MULTI_REG_VALUE);
-	emac_write(EMAC_RXMOFOVERRUNS, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_RXSOFOVERRUNS, stats_clear_mask);
+	emac_write(EMAC_RXMOFOVERRUNS, stats_clear_mask);
 
 	priv->net_dev_stats.rx_fifo_errors += emac_read(EMAC_RXDMAOVERRUNS);
-	emac_write(EMAC_RXDMAOVERRUNS, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_RXDMAOVERRUNS, stats_clear_mask);
 
 	priv->net_dev_stats.tx_carrier_errors +=
 		emac_read(EMAC_TXCARRIERSENSE);
-	emac_write(EMAC_TXCARRIERSENSE, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_TXCARRIERSENSE, stats_clear_mask);
 
 	priv->net_dev_stats.tx_fifo_errors = emac_read(EMAC_TXUNDERRUN);
-	emac_write(EMAC_TXUNDERRUN, EMAC_ALL_MULTI_REG_VALUE);
+	emac_write(EMAC_TXUNDERRUN, stats_clear_mask);
 
 	return &priv->net_dev_stats;
 }