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.

Signed-off-by: Kamil Horák - 2N <kamilh@axis.com>
---
 drivers/net/phy/phy-core.c | 1 +
 drivers/net/phy/phy_caps.c | 4 ++++
 drivers/net/phy/phylink.c  | 1 +
 include/linux/phy.h        | 4 ++++
 4 files changed, 10 insertions(+)

diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
index e177037f9110..b2df06343b7e 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 38417e288611..b4a4dea3e756 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 0faa3d97e06b..766cad40f1b8 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -234,6 +234,7 @@ 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/phy.h b/include/linux/phy.h
index e194dad1623d..6aad4b741c01 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -103,6 +103,7 @@ extern const int phy_basic_ports_array[3];
  * @PHY_INTERFACE_MODE_QUSGMII: Quad Universal SGMII
  * @PHY_INTERFACE_MODE_1000BASEKX: 1000Base-KX - with Clause 73 AN
  * @PHY_INTERFACE_MODE_10G_QXGMII: 10G-QXGMII - 4 ports over 10G USXGMII
+ * @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.
@@ -144,6 +145,7 @@ typedef enum {
 	PHY_INTERFACE_MODE_QUSGMII,
 	PHY_INTERFACE_MODE_1000BASEKX,
 	PHY_INTERFACE_MODE_10G_QXGMII,
+	PHY_INTERFACE_MODE_MIILITE,
 	PHY_INTERFACE_MODE_MAX,
 } phy_interface_t;
 
@@ -260,6 +262,8 @@ static inline const char *phy_modes(phy_interface_t interface)
 		return "qusgmii";
 	case PHY_INTERFACE_MODE_10G_QXGMII:
 		return "10g-qxgmii";
+	case PHY_INTERFACE_MODE_MIILITE:
+		return "mii-lite";
 	default:
 		return "unknown";
 	}
-- 
2.39.5

On Fri, Jun 27, 2025 at 01:23:03PM +0200, Kamil Horák - 2N wrote:
> 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.
> 
> Signed-off-by: Kamil Horák - 2N <kamilh@axis.com>

Very sorry, but in the last review, I missed that you aren't updating
the description of interfaces in Documentation/networking/phy.rst

Please see the section "PHY interface modes".

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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