[PATCH net 2/2] net: phylink: use a dedicated helper to parse usgmii control word

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Q-USGMII is a derivative of USGMII, that uses a specific formatting for
the control word. The layout is close to the USXGMII control word, but
doesn't support speeds over 1Gbps. Use a dedicated decoding logic for
the USGMII control word, re-using USXGMII definitions with a custom mask
and only considering 10/100/1000 speeds

Fixes: 5e61fe157a27 ("net: phy: Introduce QUSGMII PHY mode")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
 drivers/net/phy/phylink.c | 39 ++++++++++++++++++++++++++++++++++++++-
 include/uapi/linux/mdio.h |  3 +++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 809e6d5216dc..730f8860d2a6 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -3298,6 +3298,41 @@ void phylink_decode_usxgmii_word(struct phylink_link_state *state,
 }
 EXPORT_SYMBOL_GPL(phylink_decode_usxgmii_word);
 
+/**
+ * phylink_decode_usgmii_word() - decode the USGMII word from a MAC PCS
+ * @state: a pointer to a struct phylink_link_state.
+ * @lpa: a 16 bit value which stores the USGMII auto-negotiation word
+ *
+ * Helper for MAC PCS supporting the USGMII protocol and the auto-negotiation
+ * code word.  Decode the USGMII code word and populate the corresponding fields
+ * (speed, duplex) into the phylink_link_state structure. The structure for this
+ * word is the same as the USXGMII word, expect it only supports speeds up to
+ * 1Gbps.
+ */
+static void phylink_decode_usgmii_word(struct phylink_link_state *state,
+				 uint16_t lpa)
+{
+	switch (lpa & MDIO_USGMII_SPD_MASK) {
+	case MDIO_USXGMII_10:
+		state->speed = SPEED_10;
+		break;
+	case MDIO_USXGMII_100:
+		state->speed = SPEED_100;
+		break;
+	case MDIO_USXGMII_1000:
+		state->speed = SPEED_1000;
+		break;
+	default:
+		state->link = false;
+		return;
+	}
+
+	if (lpa & MDIO_USXGMII_FULL_DUPLEX)
+		state->duplex = DUPLEX_FULL;
+	else
+		state->duplex = DUPLEX_HALF;
+}
+
 /**
  * phylink_mii_c22_pcs_decode_state() - Decode MAC PCS state from MII registers
  * @state: a pointer to a &struct phylink_link_state.
@@ -3335,9 +3370,11 @@ 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;
+	case PHY_INTERFACE_MODE_QUSGMII:
+		phylink_decode_usgmii_word(state, lpa);
+		break;
 
 	default:
 		state->link = false;
diff --git a/include/uapi/linux/mdio.h b/include/uapi/linux/mdio.h
index 256b463e47a6..1d20a9082507 100644
--- a/include/uapi/linux/mdio.h
+++ b/include/uapi/linux/mdio.h
@@ -444,4 +444,7 @@ static inline __u16 mdio_phy_id_c45(int prtad, int devad)
 #define MDIO_USXGMII_5000FULL		0x1a00	/* 5000Mbps full-duplex */
 #define MDIO_USXGMII_LINK		0x8000	/* PHY link with copper-side partner */
 
+/* Usgmii control word is based on Usxgmii, masking away 2.5, 5 and 10Gbps */
+#define MDIO_USGMII_SPD_MASK		0x0600
+
 #endif /* _UAPI__LINUX_MDIO_H__ */
-- 
2.40.1