6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@xxxxxxxxxxxxxxxxxxxx>
[ 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@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Woojung Huh <Woojung.huh@xxxxxxxxxxxxx>
Acked-by: Arun Ramadoss <arun.ramadoss@xxxxxxxxxxxxx>
Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/net/dsa/microchip/ksz9477.c | 4 ++++
drivers/net/dsa/microchip/ksz9477_reg.h | 1 +
2 files changed, 5 insertions(+)
diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index 353c41e031f1a..a7e8fcdf25768 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1112,6 +1112,10 @@ 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 cba3dba58bc37..a2ef4b18349c4 100644
--- a/drivers/net/dsa/microchip/ksz9477_reg.h
+++ b/drivers/net/dsa/microchip/ksz9477_reg.h
@@ -267,6 +267,7 @@
#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)
--
2.43.0
