net: phy: Introduce QUSGMII PHY mode

The QUSGMII mode is a derivative of Cisco's USXGMII standard. This
standard is pretty similar to SGMII, but allows for faster speeds, and
has the build-in bits for Quad and Octa variants (like QSGMII).

The main difference with SGMII/QSGMII is that USXGMII/QUSGMII re-uses
the preamble to carry various information, named 'Extensions'.

As of today, the USXGMII standard only mentions the "PCH" extension,
which is used to convey timestamps, allowing in-band signaling of PTP
timestamps without having to modify the frame itself.

This commit adds support for that mode. When no extension is in use, it
behaves exactly like QSGMII, although it's not compatible with QSGMII.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/phy.rst

@@ -308,6 +308,15 @@ Some of the interface modes are described below:
     rate of 125Mpbs using a 4B/5B encoding scheme, resulting in an underlying
     data rate of 100Mpbs.
 
+``PHY_INTERFACE_MODE_QUSGMII``
+    This defines the Cisco the Quad USGMII mode, which is the Quad variant of
+    the USGMII (Universal SGMII) link. It's very similar to QSGMII, but uses
+    a Packet Control Header (PCH) instead of the 7 bytes preamble to carry not
+    only the port id, but also so-called "extensions". The only documented
+    extension so-far in the specification is the inclusion of timestamps, for
+    PTP-enabled PHYs. This mode isn't compatible with QSGMII, but offers the
+    same capabilities in terms of link speed and negociation.
+
 Pause frames / flow control
 ===========================
 

drivers/net/phy/phylink.c

@@ -321,6 +321,7 @@ void phylink_get_linkmodes(unsigned long *linkmodes, phy_interface_t interface,
 	case PHY_INTERFACE_MODE_RGMII_ID:
 	case PHY_INTERFACE_MODE_RGMII:
 	case PHY_INTERFACE_MODE_QSGMII:
+	case PHY_INTERFACE_MODE_QUSGMII:
 	case PHY_INTERFACE_MODE_SGMII:
 	case PHY_INTERFACE_MODE_GMII:
 		caps |= MAC_1000HD | MAC_1000FD;
@@ -632,6 +633,7 @@ static int phylink_parse_mode(struct phylink *pl, struct fwnode_handle *fwnode)
 		switch (pl->link_config.interface) {
 		case PHY_INTERFACE_MODE_SGMII:
 		case PHY_INTERFACE_MODE_QSGMII:
+		case PHY_INTERFACE_MODE_QUSGMII:
 			phylink_set(pl->supported, 10baseT_Half);
 			phylink_set(pl->supported, 10baseT_Full);
 			phylink_set(pl->supported, 100baseT_Half);
@@ -2929,6 +2931,7 @@ void phylink_mii_c22_pcs_decode_state(struct phylink_link_state *state,
 
 	case PHY_INTERFACE_MODE_SGMII:
 	case PHY_INTERFACE_MODE_QSGMII:
+	case PHY_INTERFACE_MODE_QUSGMII:
 		phylink_decode_sgmii_word(state, lpa);
 		break;
 

include/linux/phy.h

@@ -115,6 +115,7 @@ extern const int phy_10gbit_features_array[1];
  * @PHY_INTERFACE_MODE_25GBASER: 25G BaseR
  * @PHY_INTERFACE_MODE_USXGMII:  Universal Serial 10GE MII
  * @PHY_INTERFACE_MODE_10GKR: 10GBASE-KR - with Clause 73 AN
+ * @PHY_INTERFACE_MODE_QUSGMII: Quad Universal SGMII
  * @PHY_INTERFACE_MODE_MAX: Book keeping
  *
  * Describes the interface between the MAC and PHY.
@@ -152,6 +153,7 @@ typedef enum {
 	PHY_INTERFACE_MODE_USXGMII,
 	/* 10GBASE-KR - with Clause 73 AN */
 	PHY_INTERFACE_MODE_10GKR,
+	PHY_INTERFACE_MODE_QUSGMII,
 	PHY_INTERFACE_MODE_MAX,
 } phy_interface_t;
 
@@ -267,6 +269,8 @@ static inline const char *phy_modes(phy_interface_t interface)
 		return "10gbase-kr";
 	case PHY_INTERFACE_MODE_100BASEX:
 		return "100base-x";
+	case PHY_INTERFACE_MODE_QUSGMII:
+		return "qusgmii";
 	default:
 		return "unknown";
 	}