net: dsa: microchip: use collision based back pressure mode

[ Upstream commit d963c95bc9840d070a788c35e41b715a648717f7 ]

Errata DS80000758 states that carrier sense back pressure mode can cause
link down issues in 100BASE-TX half duplex mode. The datasheet also
recommends to always use the collision based back pressure mode.

Fixes: b987e98e50ab ("dsa: add DSA switch driver for Microchip KSZ9477")
Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@savoirfairelinux.com>
Reviewed-by: Woojung Huh <Woojung.huh@microchip.com>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index 05767d3025f77e850842d0faff240ecf18df382c..dde5c65c2c366dddad55ad308b34818ae65b6fbb 100644 (file)
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1303,6 +1303,10 @@ int ksz9477_setup(struct dsa_switch *ds)
        /* Enable REG_SW_MTU__2 reg by setting SW_JUMBO_PACKET */
        ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_JUMBO_PACKET, true);
 
+       /* Use collision based back pressure mode. */
+       ksz_cfg(dev, REG_SW_MAC_CTRL_1, SW_BACK_PRESSURE,
+               SW_BACK_PRESSURE_COLLISION);
+
        /* Now we can configure default MTU value */
        ret = regmap_update_bits(ksz_regmap_16(dev), REG_SW_MTU__2, REG_SW_MTU_MASK,
                                 VLAN_ETH_FRAME_LEN + ETH_FCS_LEN);

diff --git a/drivers/net/dsa/microchip/ksz9477_reg.h b/drivers/net/dsa/microchip/ksz9477_reg.h
index f3a205ee483f2133bcd79602941255842053784c..fb124be8edd30dd28b8bd47c70312fda45b1db6a 100644 (file)
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -247,6 +247,7 @@
 #define REG_SW_MAC_CTRL_1              0x0331
 
 #define SW_BACK_PRESSURE               BIT(5)
+#define SW_BACK_PRESSURE_COLLISION     0
 #define FAIR_FLOW_CTRL                 BIT(4)
 #define NO_EXC_COLLISION_DROP          BIT(3)
 #define SW_JUMBO_PACKET                        BIT(2)