net: mscc: ocelot: report ndo_get_stats64 from the wraparound-resistant ocelot->stats

Rather than reading the stats64 counters directly from the 32-bit
hardware, it's better to rely on the output produced by the periodic
ocelot_port_update_stats().

It would be even better to call ocelot_port_update_stats() right from
ocelot_get_stats64() to make sure we report the current values rather
than the ones from 2 seconds ago. But we need to export
ocelot_port_update_stats() from the switch lib towards the switchdev
driver for that, and future work will largely undo that.

There are more ocelot-based drivers waiting to be introduced, an example
of which is the SPI-controlled VSC7512. In that driver's case, it will
be impossible to call ocelot_port_update_stats() from ndo_get_stats64
context, since the latter is atomic, and reading the stats over SPI is
sleepable. So the compromise taken here, which will also hold going
forward, is to report 64-bit counters to stats64, which are not 100% up
to date.

Fixes: a556c76adc05 ("net: mscc: Add initial Ocelot switch support")
Signed-off-by: Vladimir Oltean <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/mscc/ocelot_net.c

···
 	struct ocelot_port_private *priv = netdev_priv(dev);
 	struct ocelot *ocelot = priv->port.ocelot;
 	int port = priv->port.index;
+	u64 *s;
 
 	spin_lock(&ocelot->stats_lock);
 
-	/* Configure the port to read the stats from */
-	ocelot_write(ocelot, SYS_STAT_CFG_STAT_VIEW(port),
-		     SYS_STAT_CFG);
+	s = &ocelot->stats[port * OCELOT_NUM_STATS];
 
 	/* Get Rx stats */
-	stats->rx_bytes = ocelot_read(ocelot, SYS_COUNT_RX_OCTETS);
-	stats->rx_packets = ocelot_read(ocelot, SYS_COUNT_RX_SHORTS) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_FRAGMENTS) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_JABBERS) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_LONGS) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_64) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_65_127) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_128_255) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_256_511) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_512_1023) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_1024_1526) +
-			    ocelot_read(ocelot, SYS_COUNT_RX_1527_MAX);
-	stats->multicast = ocelot_read(ocelot, SYS_COUNT_RX_MULTICAST);
+	stats->rx_bytes = s[OCELOT_STAT_RX_OCTETS];
+	stats->rx_packets = s[OCELOT_STAT_RX_SHORTS] +
+			    s[OCELOT_STAT_RX_FRAGMENTS] +
+			    s[OCELOT_STAT_RX_JABBERS] +
+			    s[OCELOT_STAT_RX_LONGS] +
+			    s[OCELOT_STAT_RX_64] +
+			    s[OCELOT_STAT_RX_65_127] +
+			    s[OCELOT_STAT_RX_128_255] +
+			    s[OCELOT_STAT_RX_256_511] +
+			    s[OCELOT_STAT_RX_512_1023] +
+			    s[OCELOT_STAT_RX_1024_1526] +
+			    s[OCELOT_STAT_RX_1527_MAX];
+	stats->multicast = s[OCELOT_STAT_RX_MULTICAST];
 	stats->rx_dropped = dev->stats.rx_dropped;
 
 	/* Get Tx stats */
-	stats->tx_bytes = ocelot_read(ocelot, SYS_COUNT_TX_OCTETS);
-	stats->tx_packets = ocelot_read(ocelot, SYS_COUNT_TX_64) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_65_127) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_128_255) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_256_511) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_512_1023) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_1024_1526) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_1527_MAX);
-	stats->tx_dropped = ocelot_read(ocelot, SYS_COUNT_TX_DROPS) +
-			    ocelot_read(ocelot, SYS_COUNT_TX_AGING);
-	stats->collisions = ocelot_read(ocelot, SYS_COUNT_TX_COLLISION);
+	stats->tx_bytes = s[OCELOT_STAT_TX_OCTETS];
+	stats->tx_packets = s[OCELOT_STAT_TX_64] +
+			    s[OCELOT_STAT_TX_65_127] +
+			    s[OCELOT_STAT_TX_128_255] +
+			    s[OCELOT_STAT_TX_256_511] +
+			    s[OCELOT_STAT_TX_512_1023] +
+			    s[OCELOT_STAT_TX_1024_1526] +
+			    s[OCELOT_STAT_TX_1527_MAX];
+	stats->tx_dropped = s[OCELOT_STAT_TX_DROPS] +
+			    s[OCELOT_STAT_TX_AGED];
+	stats->collisions = s[OCELOT_STAT_TX_COLLISION];
 
 	spin_unlock(&ocelot->stats_lock);
 }