netdev - [PATCH net-next v3 1/3] net: phy: MII-Lite PHY interface mode

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Message-ID: <20250625163453.2567869-2-kamilh@axis.com>
Date: Wed, 25 Jun 2025 18:34:51 +0200
From: Kamil Horák - 2N <kamilh@...s.com>
To: <florian.fainelli@...adcom.com>, <bcm-kernel-feedback-list@...adcom.com>,
	<andrew@...n.ch>, <hkallweit1@...il.com>, <linux@...linux.org.uk>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>
CC: <kamilh@...s.com>, <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <f.fainelli@...il.com>, <robh@...nel.org>
Subject: [PATCH net-next v3 1/3] net: phy: MII-Lite PHY interface mode

From: Kamil Horák (2N) <kamilh@...s.com>

Some Broadcom PHYs are capable to operate in simplified MII mode,
without TXER, RXER, CRS and COL signals as defined for the MII.
The MII-Lite mode can be used on most Ethernet controllers with full
MII interface by just leaving the input signals (RXER, CRS, COL)
inactive. The absence of COL signal makes half-duplex link modes
impossible but does not interfere with BroadR-Reach link modes on
Broadcom PHYs, because they are all full-duplex only.

Add MII-Lite interface mode, especially for Broadcom two-wire PHYs.
Add MII-Lite activation for bcm5481x PHYs.

Signed-off-by: Kamil Horák (2N) <kamilh@...s.com>
---
 drivers/net/phy/broadcom.c | 7 +++++++
 drivers/net/phy/phy-core.c | 1 +
 drivers/net/phy/phy_caps.c | 4 ++++
 drivers/net/phy/phylink.c  | 1 +
 include/linux/brcmphy.h    | 6 ++++++
 include/linux/phy.h        | 4 ++++
 6 files changed, 23 insertions(+)

diff --git a/drivers/net/phy/broadcom.c b/drivers/net/phy/broadcom.c
index 9b1de54fd483..7d3b85a07b8c 100644
--- a/drivers/net/phy/broadcom.c
+++ b/drivers/net/phy/broadcom.c
@@ -423,6 +423,13 @@ static int bcm54811_config_init(struct phy_device *phydev)
 	/* With BCM54811, BroadR-Reach implies no autoneg */
 	if (priv->brr_mode)
 		phydev->autoneg = 0;
+	/* Enable MII Lite (No TXER, RXER, CRS, COL) if configured */
+	err = bcm_phy_modify_exp(phydev, BCM_EXP_SYNC_ETHERNET,
+				 BCM_EXP_SYNC_ETHERNET_MII_LITE,
+				 phydev->interface == PHY_INTERFACE_MODE_MIILITE ?
+				 BCM_EXP_SYNC_ETHERNET_MII_LITE : 0);
+	if (err < 0)
+		return err;
 
 	return bcm5481x_set_brrmode(phydev, priv->brr_mode);
 }
diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
index c480bb40fa73..605ca20ae192 100644
--- a/drivers/net/phy/phy-core.c
+++ b/drivers/net/phy/phy-core.c
@@ -115,6 +115,7 @@ int phy_interface_num_ports(phy_interface_t interface)
 		return 0;
 	case PHY_INTERFACE_MODE_INTERNAL:
 	case PHY_INTERFACE_MODE_MII:
+	case PHY_INTERFACE_MODE_MIILITE:
 	case PHY_INTERFACE_MODE_GMII:
 	case PHY_INTERFACE_MODE_TBI:
 	case PHY_INTERFACE_MODE_REVMII:
diff --git a/drivers/net/phy/phy_caps.c b/drivers/net/phy/phy_caps.c
index d11ce1c7e712..2cc9ee97e867 100644
--- a/drivers/net/phy/phy_caps.c
+++ b/drivers/net/phy/phy_caps.c
@@ -316,6 +316,10 @@ unsigned long phy_caps_from_interface(phy_interface_t interface)
 		link_caps |= BIT(LINK_CAPA_100HD) | BIT(LINK_CAPA_100FD);
 		break;
 
+	case PHY_INTERFACE_MODE_MIILITE:
+		link_caps |= BIT(LINK_CAPA_10FD) | BIT(LINK_CAPA_100FD);
+		break;
+
 	case PHY_INTERFACE_MODE_TBI:
 	case PHY_INTERFACE_MODE_MOCA:
 	case PHY_INTERFACE_MODE_RTBI:
diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 67218d278ce6..5eb0a90cb3d5 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -237,6 +237,7 @@ static int phylink_interface_max_speed(phy_interface_t interface)
 	case PHY_INTERFACE_MODE_SMII:
 	case PHY_INTERFACE_MODE_REVMII:
 	case PHY_INTERFACE_MODE_MII:
+	case PHY_INTERFACE_MODE_MIILITE:
 		return SPEED_100;
 
 	case PHY_INTERFACE_MODE_TBI:
diff --git a/include/linux/brcmphy.h b/include/linux/brcmphy.h
index 028b3e00378e..15c35655f482 100644
--- a/include/linux/brcmphy.h
+++ b/include/linux/brcmphy.h
@@ -182,6 +182,12 @@
 #define BCM_LED_MULTICOLOR_ACT		0x9
 #define BCM_LED_MULTICOLOR_PROGRAM	0xa
 
+/*
+ * Broadcom Synchronous Ethernet Controls (expansion register 0x0E)
+ */
+#define BCM_EXP_SYNC_ETHERNET		(MII_BCM54XX_EXP_SEL_ER + 0x0E)
+#define BCM_EXP_SYNC_ETHERNET_MII_LITE	BIT(11)
+
 /*
  * BCM5482: Shadow registers
  * Shadow values go into bits [14:10] of register 0x1c to select a shadow
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 74c1bcf64b3c..70ac7dc795fc 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -106,6 +106,7 @@ extern const int phy_basic_ports_array[3];
  * @PHY_INTERFACE_MODE_50GBASER: 50GBase-R - with Clause 134 FEC
  * @PHY_INTERFACE_MODE_LAUI: 50 Gigabit Attachment Unit Interface
  * @PHY_INTERFACE_MODE_100GBASEP: 100GBase-P - with Clause 134 FEC
+ * @PHY_INTERFACE_MODE_MIILITE: MII Lite - MII without RXER TXER CRS COL
  * @PHY_INTERFACE_MODE_MAX: Book keeping
  *
  * Describes the interface between the MAC and PHY.
@@ -150,6 +151,7 @@ typedef enum {
 	PHY_INTERFACE_MODE_50GBASER,
 	PHY_INTERFACE_MODE_LAUI,
 	PHY_INTERFACE_MODE_100GBASEP,
+	PHY_INTERFACE_MODE_MIILITE,
 	PHY_INTERFACE_MODE_MAX,
 } phy_interface_t;
 
@@ -272,6 +274,8 @@ static inline const char *phy_modes(phy_interface_t interface)
 		return "laui";
 	case PHY_INTERFACE_MODE_100GBASEP:
 		return "100gbase-p";
+	case PHY_INTERFACE_MODE_MIILITE:
+		return "mii-lite";
 	default:
 		return "unknown";
 	}
-- 
2.39.5