net: dsa: sja1105: Prevent PHY jabbering during switch reset

Resetting the switch at runtime is currently done while changing the
vlan_filtering setting (due to the required TPID change).

But reset is asynchronous with packet egress, and the switch core will
not wait for egress to finish before carrying on with the reset
operation.

As a result, a connected PHY such as the BCM5464 would see an
unterminated Ethernet frame and start to jabber (repeat the last seen
Ethernet symbols - jabber is by definition an oversized Ethernet frame
with bad FCS). This behavior is strange in itself, but it also causes
the MACs of some link partners (such as the FRDM-LS1012A) to completely
lock up.

So as a remedy for this situation, when switch reset is required, simply
inhibit Tx on all ports, and wait for the necessary time for the
eventual one frame left in the egress queue (not even the Tx inhibit
command is instantaneous) to be flushed.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/sja1105/sja1105.h

@@ -22,6 +22,7 @@ struct sja1105_regs {
 	u64 device_id;
 	u64 prod_id;
 	u64 status;
+	u64 port_control;
 	u64 rgu;
 	u64 config;
 	u64 rmii_pll1;

drivers/net/dsa/sja1105/sja1105_spi.c

@@ -7,6 +7,7 @@
 #include <linux/packing.h>
 #include "sja1105.h"
 
+#define SJA1105_SIZE_PORT_CTRL		4
 #define SJA1105_SIZE_RESET_CMD		4
 #define SJA1105_SIZE_SPI_MSG_HEADER	4
 #define SJA1105_SIZE_SPI_MSG_MAXLEN	(64 * 4)
@@ -282,6 +283,25 @@ static int sja1105_cold_reset(const struct sja1105_private *priv)
 	return priv->info->reset_cmd(priv, &reset);
 }
 
+static int sja1105_inhibit_tx(const struct sja1105_private *priv,
+			      const unsigned long *port_bitmap)
+{
+	const struct sja1105_regs *regs = priv->info->regs;
+	u64 inhibit_cmd;
+	int port, rc;
+
+	rc = sja1105_spi_send_int(priv, SPI_READ, regs->port_control,
+				  &inhibit_cmd, SJA1105_SIZE_PORT_CTRL);
+	if (rc < 0)
+		return rc;
+
+	for_each_set_bit(port, port_bitmap, SJA1105_NUM_PORTS)
+		inhibit_cmd |= BIT(port);
+
+	return sja1105_spi_send_int(priv, SPI_WRITE, regs->port_control,
+				    &inhibit_cmd, SJA1105_SIZE_PORT_CTRL);
+}
+
 struct sja1105_status {
 	u64 configs;
 	u64 crcchkl;
@@ -370,6 +390,7 @@ static_config_buf_prepare_for_upload(struct sja1105_private *priv,
 
 int sja1105_static_config_upload(struct sja1105_private *priv)
 {
+	unsigned long port_bitmap = GENMASK_ULL(SJA1105_NUM_PORTS - 1, 0);
 	struct sja1105_static_config *config = &priv->static_config;
 	const struct sja1105_regs *regs = priv->info->regs;
 	struct device *dev = &priv->spidev->dev;
@@ -388,6 +409,20 @@ int sja1105_static_config_upload(struct sja1105_private *priv)
 		dev_err(dev, "Invalid config, cannot upload\n");
 		return -EINVAL;
 	}
+	/* Prevent PHY jabbering during switch reset by inhibiting
+	 * Tx on all ports and waiting for current packet to drain.
+	 * Otherwise, the PHY will see an unterminated Ethernet packet.
+	 */
+	rc = sja1105_inhibit_tx(priv, &port_bitmap);
+	if (rc < 0) {
+		dev_err(dev, "Failed to inhibit Tx on ports\n");
+		return -ENXIO;
+	}
+	/* Wait for an eventual egress packet to finish transmission
+	 * (reach IFG). It is guaranteed that a second one will not
+	 * follow, and that switch cold reset is thus safe
+	 */
+	usleep_range(500, 1000);
 	do {
 		/* Put the SJA1105 in programming mode */
 		rc = sja1105_cold_reset(priv);
@@ -452,6 +487,7 @@ struct sja1105_regs sja1105et_regs = {
 	.device_id = 0x0,
 	.prod_id = 0x100BC3,
 	.status = 0x1,
+	.port_control = 0x11,
 	.config = 0x020000,
 	.rgu = 0x100440,
 	.pad_mii_tx = {0x100800, 0x100802, 0x100804, 0x100806, 0x100808},
@@ -476,6 +512,7 @@ struct sja1105_regs sja1105pqrs_regs = {
 	.device_id = 0x0,
 	.prod_id = 0x100BC3,
 	.status = 0x1,
+	.port_control = 0x12,
 	.config = 0x020000,
 	.rgu = 0x100440,
 	.pad_mii_tx = {0x100800, 0x100802, 0x100804, 0x100806, 0x100808},