[PATCH v1 net] net: dsa: microchip: fix initial port flush problem

[<Tristram.Ha@microchip.com>]

From: Tristram Ha <tristram.ha@microchip.com>

The very first flush in any port will flush all learned addresses in all
ports.  This can be observed by unplugging the cable from one port while
additional ports are connected and dumping the fdb entries.

This problem is caused by the initially wrong value programmed to the
REG_SW_LUE_CTRL_1 register.  Setting SW_FLUSH_STP_TABLE and
SW_FLUSH_MSTP_TABLE bits does not have an immediate effect.  It is when
ksz9477_flush_dyn_mac_table() is called then the SW_FLUSH_STP_TABLE bit
takes effect and flushes all learned entries.  After that call both bits
are reset and so the next port flush will not cause such problem again.

Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
---
v1
 - explain how the 2 extra bits affect the flushing operation
 - write directly to disable the default SW_FWD_MCAST_SRC_ADDR bit and so
   no need to read the register first

 drivers/net/dsa/microchip/ksz9477.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index f8ad7833f5d9..2231128eef8b 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -355,10 +355,8 @@ int ksz9477_reset_switch(struct ksz_device *dev)
 			   SPI_AUTO_EDGE_DETECTION, 0);
 
 	/* default configuration */
-	ksz_read8(dev, REG_SW_LUE_CTRL_1, &data8);
-	data8 = SW_AGING_ENABLE | SW_LINK_AUTO_AGING |
-	      SW_SRC_ADDR_FILTER | SW_FLUSH_STP_TABLE | SW_FLUSH_MSTP_TABLE;
-	ksz_write8(dev, REG_SW_LUE_CTRL_1, data8);
+	ksz_write8(dev, REG_SW_LUE_CTRL_1,
+		   SW_AGING_ENABLE | SW_LINK_AUTO_AGING | SW_SRC_ADDR_FILTER);
 
 	/* disable interrupts */
 	ksz_write32(dev, REG_SW_INT_MASK__4, SWITCH_INT_MASK);
-- 
2.34.1