linux-kernel - [PATCH net-next v1 2/3] net: dsa: microchip: lan937x: force RGMII interface into PHY mode

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Date: Thu, 27 Jun 2024 14:39:10 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "David S. Miller" <davem@...emloft.net>,
	Andrew Lunn <andrew@...n.ch>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>
Cc: Lucas Stach <l.stach@...gutronix.de>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com
Subject: [PATCH net-next v1 2/3] net: dsa: microchip: lan937x: force RGMII interface into PHY mode

From: Lucas Stach <l.stach@...gutronix.de>

The register manual and datasheet documentation for the LAN937x series
disagree about the polarity of the MII mode strap. As a consequence
there are hardware designs that have the RGMII interface strapped into
MAC mode, which is a invalid configuration and will prevent the internal
clock from being fed into the port TX interface.

Force the MII mode to PHY for RGMII interfaces where this is the only
valid mode, to override the inproper strapping.

Signed-off-by: Lucas Stach <l.stach@...gutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/net/dsa/microchip/lan937x_main.c | 11 +++++++++++
 drivers/net/dsa/microchip/lan937x_reg.h  |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/drivers/net/dsa/microchip/lan937x_main.c b/drivers/net/dsa/microchip/lan937x_main.c
index e907a5602035c..b6ef48a655735 100644
--- a/drivers/net/dsa/microchip/lan937x_main.c
+++ b/drivers/net/dsa/microchip/lan937x_main.c
@@ -217,6 +217,17 @@ void lan937x_config_cpu_port(struct dsa_switch *ds)
 		if (dev->info->cpu_ports & (1 << dp->index)) {
 			dev->cpu_port = dp->index;
 
+			/*
+			 * Force RGMII interface into PHY mode, as that's the
+			 * only valid mode, but it may be in MAC mode due to
+			 * incorrect strapping.
+			 */
+			if (phy_interface_mode_is_rgmii(dev->ports[dp->index].interface)) {
+				lan937x_port_cfg(dev, dp->index,
+						 REG_PORT_XMII_CTRL_1,
+						 PORT_MII_MODE_MAC, false);
+			}
+
 			/* enable cpu port */
 			lan937x_port_setup(dev, dp->index, true);
 		}
diff --git a/drivers/net/dsa/microchip/lan937x_reg.h b/drivers/net/dsa/microchip/lan937x_reg.h
index 7ecada9240233..e36bcb155f545 100644
--- a/drivers/net/dsa/microchip/lan937x_reg.h
+++ b/drivers/net/dsa/microchip/lan937x_reg.h
@@ -150,6 +150,9 @@
 #define REG_PORT_TX_PHY_CTRL_BASE	0x0280
 
 /* 3 - xMII */
+#define REG_PORT_XMII_CTRL_1		0x0301
+#define PORT_MII_MODE_MAC		BIT(2)
+
 #define PORT_SGMII_SEL			BIT(7)
 #define PORT_GRXC_ENABLE		BIT(0)
 
-- 
2.39.2