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

[ Upstream commit d963c95 ] 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: b987e98 ("dsa: add DSA switch driver for Microchip KSZ9477") Signed-off-by: Enguerrand de Ribaucourt <[email protected]> Reviewed-by: Woojung Huh <[email protected]> Acked-by: Arun Ramadoss <[email protected]> Reviewed-by: Andrew Lunn <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Sasha Levin <[email protected]>
3003n · Jul 5, 2024 · 5add250 · 5add250
1 parent c553ba2
commit 5add250
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diff --git 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
@@ -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)