netdev - [PATCH net v5 3/4] net: dsa: microchip: use collision based back pressure mode

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Date: Tue,  4 Jun 2024 09:23:04 +0000
From: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@...oirfairelinux.com>
To: netdev@...r.kernel.org
Cc: andrew@...n.ch,
	hkallweit1@...il.com,
	linux@...linux.org.uk,
	woojung.huh@...rochip.com,
	UNGLinuxDriver@...rochip.com,
	horms@...nel.org,
	Tristram.Ha@...rochip.com,
	Arun.Ramadoss@...rochip.com,
	Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@...oirfairelinux.com>
Subject: [PATCH net v5 3/4] net: dsa: microchip: use collision based back pressure mode

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@...oirfairelinux.com>
---
v5:
 - define SW_BACK_PRESSURE_COLLISION
v4: https://lore.kernel.org/all/20240531142430.678198-5-enguerrand.de-ribaucourt@savoirfairelinux.com/
 - rebase on net/main
 - add Fixes tag
v3: https://lore.kernel.org/all/20240530102436.226189-5-enguerrand.de-ribaucourt@savoirfairelinux.com/
---
 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 f8ad7833f5d9..c2878dd0ad7e 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -1299,6 +1299,10 @@ 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 f3a205ee483f..fb124be8edd3 100644
--- 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)
-- 
2.34.1