Subject: [PATCH RFC net-next 1/9] net: phylink: add phylink_pcs_neg_mode()

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 23 May 2023 16:55:10 +0100

Signed-off-by: Russell King (Oracle) <[email-masked]>
---
 include/linux/phylink.h | 76 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/include/linux/phylink.h b/include/linux/phylink.h
index 0cf07d7d11b8..e3cb0b4eed1d 100644
--- a/include/linux/phylink.h
+++ b/include/linux/phylink.h
@@ -21,6 +21,18 @@ enum {
 	MLO_AN_FIXED,	/* Fixed-link mode */
 	MLO_AN_INBAND,	/* In-band protocol */
 
+	/* PCS "negotiation" mode.
+	 *  PHYLINK_PCS_NEG_NONE - protocol has no inband capability
+	 *  PHYLINK_PCS_NEG_OUTBAND - some out of band or fixed link setting
+	 *  PHYLINK_PCS_NEG_INBAND_DISABLED - inband mode disabled, e.g.
+	 *				      1000base-X with autoneg off
+	 *  PHYLINK_PCS_NEG_INBAND_ENABLED - inband mode enabled
+	 */
+	PHYLINK_PCS_NEG_NONE = 0,
+	PHYLINK_PCS_NEG_OUTBAND,
+	PHYLINK_PCS_NEG_INBAND_DISABLED,
+	PHYLINK_PCS_NEG_INBAND_ENABLED,
+
 	/* MAC_SYM_PAUSE and MAC_ASYM_PAUSE are used when configuring our
 	 * autonegotiation advertisement. They correspond to the PAUSE and
 	 * ASM_DIR bits defined by 802.3, respectively.
@@ -79,6 +91,70 @@ static inline bool phylink_autoneg_inband(unsigned int mode)
 	return mode == MLO_AN_INBAND;
 }
 
+/**
+ * phylink_pcs_neg_mode() - helper to determine PCS inband mode
+ * @mode: one of %MLO_AN_FIXED, %MLO_AN_PHY, %MLO_AN_INBAND.
+ * @interface: interface mode to be used
+ * @advertising: adertisement ethtool link mode mask
+ *
+ * Determines the negotiation mode to be used by the PCS, and returns
+ * one of:
+ * %PHYLINK_PCS_NEG_NONE: interface mode does not support inband
+ * %PHYLINK_PCS_NEG_OUTBAND: an out of band mode (e.g. reading the PHY)
+ *   will be used.
+ * %PHYLINK_PCS_NEG_INBAND_DISABLED: inband mode selected but autoneg disabled
+ * %PHYLINK_PCS_NEG_INBAND_ENABLED: inband mode selected and autoneg enabled
+ *
+ * Note: this is for cases where the PCS itself is involved in negotiation
+ * (e.g. Clause 37, SGMII and similar) not Clause 73.
+ */
+static inline unsigned int phylink_pcs_neg_mode(unsigned int mode,
+						phy_interface_t interface,
+						const unsigned long *advertising)
+{
+	unsigned int neg_mode;
+
+	switch (interface) {
+	case PHY_INTERFACE_MODE_SGMII:
+	case PHY_INTERFACE_MODE_QSGMII:
+	case PHY_INTERFACE_MODE_QUSGMII:
+	case PHY_INTERFACE_MODE_USXGMII:
+		/* These protocols are designed for use with a PHY which
+		 * communicates its negotiation result back to the MAC via
+		 * inband communication. Note: there exist PHYs that run
+		 * with SGMII but do not send the inband data.
+		 */
+		if (!phylink_autoneg_inband(mode))
+			neg_mode = PHYLINK_PCS_NEG_OUTBAND;
+		else
+			neg_mode = PHYLINK_PCS_NEG_INBAND_ENABLED;
+		break;
+
+	case PHY_INTERFACE_MODE_1000BASEX:
+	case PHY_INTERFACE_MODE_2500BASEX:
+		/* 1000base-X is designed for use media-side for Fibre
+		 * connections, and thus the Autoneg bit needs to be
+		 * taken into account. We also do this for 2500base-X
+		 * as well, but drivers may not support this, so may
+		 * need to override this.
+		 */
+		if (!phylink_autoneg_inband(mode))
+			neg_mode = PHYLINK_PCS_NEG_OUTBAND;
+		else if (linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
+					   advertising))
+			neg_mode = PHYLINK_PCS_NEG_INBAND_ENABLED;
+		else
+			neg_mode = PHYLINK_PCS_NEG_INBAND_DISABLED;
+		break;
+
+	default:
+		neg_mode = PHYLINK_PCS_NEG_NONE;
+		break;
+	}
+
+	return neg_mode;
+}
+
 /**
  * struct phylink_link_state - link state structure
  * @advertising: ethtool bitmask containing advertised link modes
-- 
2.30.2