net: qca_spi: Avoid re-sync for single signature error

Setting a new network key would cause a reset of the QCA7000. Usually
the driver only notice the SPI interrupt and a single signature error.
So avoid the whole re-sync process (possible packet loss, transmit queue
stop and no carrier for at least 1 second) in this case.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/qca_spi.c

@@ -524,8 +524,11 @@ qcaspi_qca7k_sync(struct qcaspi *qca, int event)
 
 	switch (qca->sync) {
 	case QCASPI_SYNC_READY:
-		/* Read signature, if not valid go to unknown state. */
+		/* Check signature twice, if not valid go to unknown state. */
 		qcaspi_read_register(qca, SPI_REG_SIGNATURE, &signature);
+		if (signature != QCASPI_GOOD_SIGNATURE)
+			qcaspi_read_register(qca, SPI_REG_SIGNATURE, &signature);
+
 		if (signature != QCASPI_GOOD_SIGNATURE) {
 			qca->sync = QCASPI_SYNC_UNKNOWN;
 			netdev_dbg(qca->net_dev, "sync: bad signature, restart\n");