Merge branch 'net-add-negotiation-of-in-band-capabilities'

Russell King says:

====================
net: add negotiation of in-band capabilities

This is a repost without RFC for this series, shrunk down to 13 patches
by removing the non-Marvell PCS.

Phylink's handling of in-band has been deficient for a long time, and
people keep hitting problems with it. Notably, situations with the way-
to-late standardized 2500Base-X and whether that should or should not
have in-band enabled. We have also been carrying a hack in the form of
phylink_phy_no_inband() for a PHY that has been used on a SFP module,
but has no in-band capabilities, not even for SGMII.

When phylink is trying to operate in in-band mode, this series will look
at the capabilities of the MAC-side PCS and PHY, and work out whether
in-band can or should be used, programming the PHY as appropriate. This
includes in-band bypass mode at the PHY.

We don't... yet... support bypass on the MAC side PCS, because that
requires yet more complexity.

Patch 1 passes struct phylink and struct phylink_pcs into
phylink_pcs_neg_mode() so we can look at more state in this function in
a future patch.

Patch 2 splits "cur_link_an_mode" (the MLO_AN_* mode) into two separate
purposes - a requested and an active mode. The active mode is the one
we will be using for the MAC, which becomes dependent on the result of
in-band negotiation.

Patch 3 adds debug to phylink_major_config() so we can see what is going
on with the requested and active AN modes.

Patch 4 adds to phylib a method to get the in-band capabilities of the
PHY from phylib. Patches 5 and 6 add implementations for BCM84881 and
some Marvell PHYs found on SFPs.

Patch 7 adds to phylib a method to configure the PHY in-band signalling,
and patch 8 implements it for those Marvell PHYs that support the method
in patch 4.

Patch 9 does the same as patch 4 but for the MAC-side PCS, with patches
10 and 11 adding support to Marvell NETA and PP2.

Patch 12 adds the code to phylink_pcs_neg_mode() which looks at the
capabilities, and works out whether to use in-band or out-band mode for
driving the link between the MAC PCS and PHY.

Patch 13 removes the phylink_phy_no_inband() hack now that we are
publishing the in-band capabilities from the BCM84881 PHY driver.

Three more PCS, omitted from this series due to the limit of 15 patches,
will be sent once this has been merged.
====================

Link: https://patch.msgid.link/Z08kCwxdkU4n2V6x@shell.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

8 files changed, 474 insertions, 92 deletions

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 1fb285fa0bdb..fe6261b81540 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -3960,20 +3960,27 @@ static struct mvneta_port *mvneta_pcs_to_port(struct phylink_pcs *pcs)
 	return container_of(pcs, struct mvneta_port, phylink_pcs);
 }
 
-static int mvneta_pcs_validate(struct phylink_pcs *pcs,
-			       unsigned long *supported,
-			       const struct phylink_link_state *state)
+static unsigned int mvneta_pcs_inband_caps(struct phylink_pcs *pcs,
+					   phy_interface_t interface)
 {
-	/* We only support QSGMII, SGMII, 802.3z and RGMII modes.
-	 * When in 802.3z mode, we must have AN enabled:
+	/* When operating in an 802.3z mode, we must have AN enabled:
 	 * "Bit 2 Field InBandAnEn In-band Auto-Negotiation enable. ...
 	 * When <PortType> = 1 (1000BASE-X) this field must be set to 1."
+	 * Therefore, inband is "required".
 	 */
-	if (phy_interface_mode_is_8023z(state->interface) &&
-	    !phylink_test(state->advertising, Autoneg))
-		return -EINVAL;
+	if (phy_interface_mode_is_8023z(interface))
+		return LINK_INBAND_ENABLE;
 
-	return 0;
+	/* QSGMII, SGMII and RGMII can be configured to use inband
+	 * signalling of the AN result. Indicate these as "possible".
+	 */
+	if (interface == PHY_INTERFACE_MODE_SGMII ||
+	    interface == PHY_INTERFACE_MODE_QSGMII ||
+	    phy_interface_mode_is_rgmii(interface))
+		return LINK_INBAND_DISABLE | LINK_INBAND_ENABLE;
+
+	/* For any other modes, indicate that inband is not supported. */
+	return LINK_INBAND_DISABLE;
 }
 
 static void mvneta_pcs_get_state(struct phylink_pcs *pcs,
@@ -4071,7 +4078,7 @@ static void mvneta_pcs_an_restart(struct phylink_pcs *pcs)
 }
 
 static const struct phylink_pcs_ops mvneta_phylink_pcs_ops = {
-	.pcs_validate = mvneta_pcs_validate,
+	.pcs_inband_caps = mvneta_pcs_inband_caps,
 	.pcs_get_state = mvneta_pcs_get_state,
 	.pcs_config = mvneta_pcs_config,
 	.pcs_an_restart = mvneta_pcs_an_restart,
diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index 571631a30320..f85229a30844 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -6224,19 +6224,26 @@ static const struct phylink_pcs_ops mvpp2_phylink_xlg_pcs_ops = {
 	.pcs_config = mvpp2_xlg_pcs_config,
 };
 
-static int mvpp2_gmac_pcs_validate(struct phylink_pcs *pcs,
-				   unsigned long *supported,
-				   const struct phylink_link_state *state)
+static unsigned int mvpp2_gmac_pcs_inband_caps(struct phylink_pcs *pcs,
+					       phy_interface_t interface)
 {
-	/* When in 802.3z mode, we must have AN enabled:
+	/* When operating in an 802.3z mode, we must have AN enabled:
 	 * Bit 2 Field InBandAnEn In-band Auto-Negotiation enable. ...
 	 * When <PortType> = 1 (1000BASE-X) this field must be set to 1.
+	 * Therefore, inband is "required".
 	 */
-	if (phy_interface_mode_is_8023z(state->interface) &&
-	    !phylink_test(state->advertising, Autoneg))
-		return -EINVAL;
+	if (phy_interface_mode_is_8023z(interface))
+		return LINK_INBAND_ENABLE;
 
-	return 0;
+	/* SGMII and RGMII can be configured to use inband signalling of the
+	 * AN result. Indicate these as "possible".
+	 */
+	if (interface == PHY_INTERFACE_MODE_SGMII ||
+	    phy_interface_mode_is_rgmii(interface))
+		return LINK_INBAND_DISABLE | LINK_INBAND_ENABLE;
+
+	/* For any other modes, indicate that inband is not supported. */
+	return LINK_INBAND_DISABLE;
 }
 
 static void mvpp2_gmac_pcs_get_state(struct phylink_pcs *pcs,
@@ -6343,7 +6350,7 @@ static void mvpp2_gmac_pcs_an_restart(struct phylink_pcs *pcs)
 }
 
 static const struct phylink_pcs_ops mvpp2_phylink_gmac_pcs_ops = {
-	.pcs_validate = mvpp2_gmac_pcs_validate,
+	.pcs_inband_caps = mvpp2_gmac_pcs_inband_caps,
 	.pcs_get_state = mvpp2_gmac_pcs_get_state,
 	.pcs_config = mvpp2_gmac_pcs_config,
 	.pcs_an_restart = mvpp2_gmac_pcs_an_restart,
diff --git a/drivers/net/phy/bcm84881.c b/drivers/net/phy/bcm84881.c
index 97da3aee4942..47405bded677 100644
--- a/drivers/net/phy/bcm84881.c
+++ b/drivers/net/phy/bcm84881.c
@@ -235,11 +235,21 @@ static int bcm84881_read_status(struct phy_device *phydev)
 	return genphy_c45_read_mdix(phydev);
 }
 
+/* The Broadcom BCM84881 in the Methode DM7052 is unable to provide a SGMII
+ * or 802.3z control word, so inband will not work.
+ */
+static unsigned int bcm84881_inband_caps(struct phy_device *phydev,
+					 phy_interface_t interface)
+{
+	return LINK_INBAND_DISABLE;
+}
+
 static struct phy_driver bcm84881_drivers[] = {
 	{
 		.phy_id		= 0xae025150,
 		.phy_id_mask	= 0xfffffff0,
 		.name		= "Broadcom BCM84881",
+		.inband_caps	= bcm84881_inband_caps,
 		.config_init	= bcm84881_config_init,
 		.probe		= bcm84881_probe,
 		.get_features	= bcm84881_get_features,
diff --git a/drivers/net/phy/marvell.c b/drivers/net/phy/marvell.c
index cd50cd6a7f75..b885bc0fe6e0 100644
--- a/drivers/net/phy/marvell.c
+++ b/drivers/net/phy/marvell.c
@@ -717,6 +717,48 @@ static int marvell_config_aneg_fiber(struct phy_device *phydev)
 	return genphy_check_and_restart_aneg(phydev, changed);
 }
 
+static unsigned int m88e1111_inband_caps(struct phy_device *phydev,
+					 phy_interface_t interface)
+{
+	/* In 1000base-X and SGMII modes, the inband mode can be changed
+	 * through the Fibre page BMCR ANENABLE bit.
+	 */
+	if (interface == PHY_INTERFACE_MODE_1000BASEX ||
+	    interface == PHY_INTERFACE_MODE_SGMII)
+		return LINK_INBAND_DISABLE | LINK_INBAND_ENABLE |
+		       LINK_INBAND_BYPASS;
+
+	return 0;
+}
+
+static int m88e1111_config_inband(struct phy_device *phydev, unsigned int modes)
+{
+	u16 extsr, bmcr;
+	int err;
+
+	if (phydev->interface != PHY_INTERFACE_MODE_1000BASEX &&
+	    phydev->interface != PHY_INTERFACE_MODE_SGMII)
+		return -EINVAL;
+
+	if (modes == LINK_INBAND_BYPASS)
+		extsr = MII_M1111_HWCFG_SERIAL_AN_BYPASS;
+	else
+		extsr = 0;
+
+	if (modes == LINK_INBAND_DISABLE)
+		bmcr = 0;
+	else
+		bmcr = BMCR_ANENABLE;
+
+	err = phy_modify(phydev, MII_M1111_PHY_EXT_SR,
+			 MII_M1111_HWCFG_SERIAL_AN_BYPASS, extsr);
+	if (err < 0)
+		return extsr;
+
+	return phy_modify_paged(phydev, MII_MARVELL_FIBER_PAGE, MII_BMCR,
+				BMCR_ANENABLE, bmcr);
+}
+
 static int m88e1111_config_aneg(struct phy_device *phydev)
 {
 	int extsr = phy_read(phydev, MII_M1111_PHY_EXT_SR);
@@ -3677,6 +3719,8 @@ static struct phy_driver marvell_drivers[] = {
 		.name = "Marvell 88E1112",
 		/* PHY_GBIT_FEATURES */
 		.probe = marvell_probe,
+		.inband_caps = m88e1111_inband_caps,
+		.config_inband = m88e1111_config_inband,
 		.config_init = m88e1112_config_init,
 		.config_aneg = marvell_config_aneg,
 		.config_intr = marvell_config_intr,
@@ -3698,6 +3742,8 @@ static struct phy_driver marvell_drivers[] = {
 		/* PHY_GBIT_FEATURES */
 		.flags = PHY_POLL_CABLE_TEST,
 		.probe = marvell_probe,
+		.inband_caps = m88e1111_inband_caps,
+		.config_inband = m88e1111_config_inband,
 		.config_init = m88e1111gbe_config_init,
 		.config_aneg = m88e1111_config_aneg,
 		.read_status = marvell_read_status,
@@ -3721,6 +3767,8 @@ static struct phy_driver marvell_drivers[] = {
 		.name = "Marvell 88E1111 (Finisar)",
 		/* PHY_GBIT_FEATURES */
 		.probe = marvell_probe,
+		.inband_caps = m88e1111_inband_caps,
+		.config_inband = m88e1111_config_inband,
 		.config_init = m88e1111gbe_config_init,
 		.config_aneg = m88e1111_config_aneg,
 		.read_status = marvell_read_status,
diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index 0d20b534122b..0c228aa18019 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -1006,6 +1006,59 @@ static int phy_check_link_status(struct phy_device *phydev)
 }
 
 /**
+ * phy_inband_caps - query which in-band signalling modes are supported
+ * @phydev: a pointer to a &struct phy_device
+ * @interface: the interface mode for the PHY
+ *
+ * Returns zero if it is unknown what in-band signalling is supported by the
+ * PHY (e.g. because the PHY driver doesn't implement the method.) Otherwise,
+ * returns a bit mask of the LINK_INBAND_* values from
+ * &enum link_inband_signalling to describe which inband modes are supported
+ * by the PHY for this interface mode.
+ */
+unsigned int phy_inband_caps(struct phy_device *phydev,
+			     phy_interface_t interface)
+{
+	if (phydev->drv && phydev->drv->inband_caps)
+		return phydev->drv->inband_caps(phydev, interface);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(phy_inband_caps);
+
+/**
+ * phy_config_inband - configure the desired PHY in-band mode
+ * @phydev: the phy_device struct
+ * @modes: in-band modes to configure
+ *
+ * Description: disables, enables or enables-with-bypass in-band signalling
+ *   between the PHY and host system.
+ *
+ * Returns: zero on success, or negative errno value.
+ */
+int phy_config_inband(struct phy_device *phydev, unsigned int modes)
+{
+	int err;
+
+	if (!!(modes & LINK_INBAND_DISABLE) +
+	    !!(modes & LINK_INBAND_ENABLE) +
+	    !!(modes & LINK_INBAND_BYPASS) != 1)
+		return -EINVAL;
+
+	mutex_lock(&phydev->lock);
+	if (!phydev->drv)
+		err = -EIO;
+	else if (!phydev->drv->config_inband)
+		err = -EOPNOTSUPP;
+	else
+		err = phydev->drv->config_inband(phydev, modes);
+	mutex_unlock(&phydev->lock);
+
+	return err;
+}
+EXPORT_SYMBOL(phy_config_inband);
+
+/**
  * _phy_start_aneg - start auto-negotiation for this PHY device
  * @phydev: the phy_device struct
  *
diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 30a654e98352..95fbc363f9a6 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -56,7 +56,8 @@ struct phylink {
 	struct phy_device *phydev;
 	phy_interface_t link_interface;	/* PHY_INTERFACE_xxx */
 	u8 cfg_link_an_mode;		/* MLO_AN_xxx */
-	u8 cur_link_an_mode;
+	u8 req_link_an_mode;		/* Requested MLO_AN_xxx mode */
+	u8 act_link_an_mode;		/* Active MLO_AN_xxx mode */
 	u8 link_port;			/* The current non-phy ethtool port */
 	__ETHTOOL_DECLARE_LINK_MODE_MASK(supported);
 
@@ -74,6 +75,7 @@ struct phylink {
 
 	struct mutex state_mutex;
 	struct phylink_link_state phy_state;
+	unsigned int phy_ib_mode;
 	struct work_struct resolve;
 	unsigned int pcs_neg_mode;
 	unsigned int pcs_state;
@@ -174,6 +176,24 @@ static const char *phylink_an_mode_str(unsigned int mode)
 	return mode < ARRAY_SIZE(modestr) ? modestr[mode] : "unknown";
 }
 
+static const char *phylink_pcs_mode_str(unsigned int mode)
+{
+	if (!mode)
+		return "none";
+
+	if (mode & PHYLINK_PCS_NEG_OUTBAND)
+		return "outband";
+
+	if (mode & PHYLINK_PCS_NEG_INBAND) {
+		if (mode & PHYLINK_PCS_NEG_ENABLED)
+			return "inband,an-enabled";
+		else
+			return "inband,an-disabled";
+	}
+
+	return "unknown";
+}
+
 static unsigned int phylink_interface_signal_rate(phy_interface_t interface)
 {
 	switch (interface) {
@@ -971,6 +991,15 @@ static void phylink_resolve_an_pause(struct phylink_link_state *state)
 	}
 }
 
+static unsigned int phylink_pcs_inband_caps(struct phylink_pcs *pcs,
+				    phy_interface_t interface)
+{
+	if (pcs && pcs->ops->pcs_inband_caps)
+		return pcs->ops->pcs_inband_caps(pcs, interface);
+
+	return 0;
+}
+
 static void phylink_pcs_pre_config(struct phylink_pcs *pcs,
 				   phy_interface_t interface)
 {
@@ -1024,6 +1053,24 @@ static void phylink_pcs_link_up(struct phylink_pcs *pcs, unsigned int neg_mode,
 		pcs->ops->pcs_link_up(pcs, neg_mode, interface, speed, duplex);
 }
 
+/* Query inband for a specific interface mode, asking the MAC for the
+ * PCS which will be used to handle the interface mode.
+ */
+static unsigned int phylink_inband_caps(struct phylink *pl,
+					 phy_interface_t interface)
+{
+	struct phylink_pcs *pcs;
+
+	if (!pl->mac_ops->mac_select_pcs)
+		return 0;
+
+	pcs = pl->mac_ops->mac_select_pcs(pl->config, interface);
+	if (!pcs)
+		return 0;
+
+	return phylink_pcs_inband_caps(pcs, interface);
+}
+
 static void phylink_pcs_poll_stop(struct phylink *pl)
 {
 	if (pl->cfg_link_an_mode == MLO_AN_INBAND)
@@ -1065,13 +1112,13 @@ static void phylink_mac_config(struct phylink *pl,
 
 	phylink_dbg(pl,
 		    "%s: mode=%s/%s/%s adv=%*pb pause=%02x\n",
-		    __func__, phylink_an_mode_str(pl->cur_link_an_mode),
+		    __func__, phylink_an_mode_str(pl->act_link_an_mode),
 		    phy_modes(st.interface),
 		    phy_rate_matching_to_str(st.rate_matching),
 		    __ETHTOOL_LINK_MODE_MASK_NBITS, st.advertising,
 		    st.pause);
 
-	pl->mac_ops->mac_config(pl->config, pl->cur_link_an_mode, &st);
+	pl->mac_ops->mac_config(pl->config, pl->act_link_an_mode, &st);
 }
 
 static void phylink_pcs_an_restart(struct phylink *pl)
@@ -1079,13 +1126,14 @@ static void phylink_pcs_an_restart(struct phylink *pl)
 	if (pl->pcs && linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
 					 pl->link_config.advertising) &&
 	    phy_interface_mode_is_8023z(pl->link_config.interface) &&
-	    phylink_autoneg_inband(pl->cur_link_an_mode))
+	    phylink_autoneg_inband(pl->act_link_an_mode))
 		pl->pcs->ops->pcs_an_restart(pl->pcs);
 }
 
 /**
  * phylink_pcs_neg_mode() - helper to determine PCS inband mode
- * @mode: one of %MLO_AN_FIXED, %MLO_AN_PHY, %MLO_AN_INBAND.
+ * @pl: a pointer to a &struct phylink returned from phylink_create()
+ * @pcs: a pointer to &struct phylink_pcs
  * @interface: interface mode to be used
  * @advertising: adertisement ethtool link mode mask
  *
@@ -1102,11 +1150,21 @@ static void phylink_pcs_an_restart(struct phylink *pl)
  * Note: this is for cases where the PCS itself is involved in negotiation
  * (e.g. Clause 37, SGMII and similar) not Clause 73.
  */
-static unsigned int phylink_pcs_neg_mode(unsigned int mode,
-					 phy_interface_t interface,
-					 const unsigned long *advertising)
+static void phylink_pcs_neg_mode(struct phylink *pl, struct phylink_pcs *pcs,
+				 phy_interface_t interface,
+				 const unsigned long *advertising)
 {
-	unsigned int neg_mode;
+	unsigned int pcs_ib_caps = 0;
+	unsigned int phy_ib_caps = 0;
+	unsigned int neg_mode, mode;
+	enum {
+		INBAND_CISCO_SGMII,
+		INBAND_BASEX,
+	} type;
+
+	mode = pl->req_link_an_mode;
+
+	pl->phy_ib_mode = 0;
 
 	switch (interface) {
 	case PHY_INTERFACE_MODE_SGMII:
@@ -1119,10 +1177,7 @@ static unsigned int phylink_pcs_neg_mode(unsigned int mode,
 		 * 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;
+		type = INBAND_CISCO_SGMII;
 		break;
 
 	case PHY_INTERFACE_MODE_1000BASEX:
@@ -1133,21 +1188,143 @@ static unsigned int phylink_pcs_neg_mode(unsigned int mode,
 		 * as well, but drivers may not support this, so may
 		 * need to override this.
 		 */
-		if (!phylink_autoneg_inband(mode))
+		type = INBAND_BASEX;
+		break;
+
+	default:
+		pl->pcs_neg_mode = PHYLINK_PCS_NEG_NONE;
+		pl->act_link_an_mode = mode;
+		return;
+	}
+
+	if (pcs)
+		pcs_ib_caps = phylink_pcs_inband_caps(pcs, interface);
+
+	if (pl->phydev)
+		phy_ib_caps = phy_inband_caps(pl->phydev, interface);
+
+	phylink_dbg(pl, "interface %s inband modes: pcs=%02x phy=%02x\n",
+		    phy_modes(interface), pcs_ib_caps, phy_ib_caps);
+
+	if (!phylink_autoneg_inband(mode)) {
+		bool pcs_ib_only = false;
+		bool phy_ib_only = false;
+
+		if (pcs_ib_caps && pcs_ib_caps != LINK_INBAND_DISABLE) {
+			/* PCS supports reporting in-band capabilities, and
+			 * supports more than disable mode.
+			 */
+			if (pcs_ib_caps & LINK_INBAND_DISABLE)
+				neg_mode = PHYLINK_PCS_NEG_OUTBAND;
+			else if (pcs_ib_caps & LINK_INBAND_ENABLE)
+				pcs_ib_only = true;
+		}
+
+		if (phy_ib_caps && phy_ib_caps != LINK_INBAND_DISABLE) {
+			/* PHY supports in-band capabilities, and supports
+			 * more than disable mode.
+			 */
+			if (phy_ib_caps & LINK_INBAND_DISABLE)
+				pl->phy_ib_mode = LINK_INBAND_DISABLE;
+			else if (phy_ib_caps & LINK_INBAND_BYPASS)
+				pl->phy_ib_mode = LINK_INBAND_BYPASS;
+			else if (phy_ib_caps & LINK_INBAND_ENABLE)
+				phy_ib_only = true;
+		}
+
+		/* If either the PCS or PHY requires inband to be enabled,
+		 * this is an invalid configuration. Provide a diagnostic
+		 * message for this case, but don't try to force the issue.
+		 */
+		if (pcs_ib_only || phy_ib_only)
+			phylink_warn(pl,
+				     "firmware wants %s mode, but %s%s%s requires inband\n",
+				     phylink_an_mode_str(mode),
+				     pcs_ib_only ? "PCS" : "",
+				     pcs_ib_only && phy_ib_only ? " and " : "",
+				     phy_ib_only ? "PHY" : "");
+
+		neg_mode = PHYLINK_PCS_NEG_OUTBAND;
+	} else if (type == INBAND_CISCO_SGMII || pl->phydev) {
+		/* For SGMII modes which are designed to be used with PHYs, or
+		 * Base-X with a PHY, we try to use in-band mode where-ever
+		 * possible. However, there are some PHYs e.g. BCM84881 which
+		 * do not support in-band.
+		 */
+		const unsigned int inband_ok = LINK_INBAND_ENABLE |
+					       LINK_INBAND_BYPASS;
+		const unsigned int outband_ok = LINK_INBAND_DISABLE |
+						LINK_INBAND_BYPASS;
+		/* PCS	PHY
+		 * D E	D E
+		 * 0 0  0 0	no information			inband enabled
+		 * 1 0  0 0	pcs doesn't support		outband
+		 * 0 1  0 0	pcs required			inband enabled
+		 * 1 1  0 0	pcs optional			inband enabled
+		 * 0 0  1 0	phy doesn't support		outband
+		 * 1 0  1 0	pcs+phy doesn't support		outband
+		 * 0 1  1 0	pcs required, phy doesn't support, invalid
+		 * 1 1  1 0	pcs optional, phy doesn't support, outband
+		 * 0 0  0 1	phy required			inband enabled
+		 * 1 0  0 1	pcs doesn't support, phy required, invalid
+		 * 0 1  0 1	pcs+phy required		inband enabled
+		 * 1 1  0 1	pcs optional, phy required	inband enabled
+		 * 0 0  1 1	phy optional			inband enabled
+		 * 1 0  1 1	pcs doesn't support, phy optional, outband
+		 * 0 1  1 1	pcs required, phy optional	inband enabled
+		 * 1 1  1 1	pcs+phy optional		inband enabled
+		 */
+		if ((!pcs_ib_caps || pcs_ib_caps & inband_ok) &&
+		    (!phy_ib_caps || phy_ib_caps & inband_ok)) {
+			/* In-band supported or unknown at both ends. Enable
+			 * in-band mode with or without bypass at the PHY.
+			 */
+			if (phy_ib_caps & LINK_INBAND_ENABLE)
+				pl->phy_ib_mode = LINK_INBAND_ENABLE;
+			else if (phy_ib_caps & LINK_INBAND_BYPASS)
+				pl->phy_ib_mode = LINK_INBAND_BYPASS;
+
+			neg_mode = PHYLINK_PCS_NEG_INBAND_ENABLED;
+		} else if ((!pcs_ib_caps || pcs_ib_caps & outband_ok) &&
+			   (!phy_ib_caps || phy_ib_caps & outband_ok)) {
+			/* Either in-band not supported at at least one end.
+			 * In-band bypass at the other end is possible.
+			 */
+			if (phy_ib_caps & LINK_INBAND_DISABLE)
+				pl->phy_ib_mode = LINK_INBAND_DISABLE;
+			else if (phy_ib_caps & LINK_INBAND_BYPASS)
+				pl->phy_ib_mode = LINK_INBAND_BYPASS;
+
 			neg_mode = PHYLINK_PCS_NEG_OUTBAND;
+			if (pl->phydev)
+				mode = MLO_AN_PHY;
+		} else {
+			/* invalid */
+			phylink_warn(pl, "%s: incompatible in-band capabilities, trying in-band",
+				     phy_modes(interface));
+			neg_mode = PHYLINK_PCS_NEG_INBAND_ENABLED;
+		}
+	} else {
+		/* For Base-X without a PHY */
+		if (pcs_ib_caps == LINK_INBAND_DISABLE)
+			/* If the PCS doesn't support inband, then inband must
+			 * be disabled.
+			 */
+			neg_mode = PHYLINK_PCS_NEG_INBAND_DISABLED;
+		else if (pcs_ib_caps == LINK_INBAND_ENABLE)
+			/* If the PCS requires inband, then inband must always
+			 * be enabled.
+			 */
+			neg_mode = PHYLINK_PCS_NEG_INBAND_ENABLED;
 		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;
+	pl->pcs_neg_mode = neg_mode;
+	pl->act_link_an_mode = mode;
 }
 
 static void phylink_major_config(struct phylink *pl, bool restart,
@@ -1159,11 +1336,9 @@ static void phylink_major_config(struct phylink *pl, bool restart,
 	unsigned int neg_mode;
 	int err;
 
-	phylink_dbg(pl, "major config %s\n", phy_modes(state->interface));
-
-	pl->pcs_neg_mode = phylink_pcs_neg_mode(pl->cur_link_an_mode,
-						state->interface,
-						state->advertising);
+	phylink_dbg(pl, "major config, requested %s/%s\n",
+		    phylink_an_mode_str(pl->req_link_an_mode),
+		    phy_modes(state->interface));
 
 	if (pl->mac_ops->mac_select_pcs) {
 		pcs = pl->mac_ops->mac_select_pcs(pl->config, state->interface);
@@ -1177,10 +1352,17 @@ static void phylink_major_config(struct phylink *pl, bool restart,
 		pcs_changed = pl->pcs != pcs;
 	}
 
+	phylink_pcs_neg_mode(pl, pcs, state->interface, state->advertising);
+
+	phylink_dbg(pl, "major config, active %s/%s/%s\n",
+		    phylink_an_mode_str(pl->act_link_an_mode),
+		    phylink_pcs_mode_str(pl->pcs_neg_mode),
+		    phy_modes(state->interface));
+
 	phylink_pcs_poll_stop(pl);
 
 	if (pl->mac_ops->mac_prepare) {
-		err = pl->mac_ops->mac_prepare(pl->config, pl->cur_link_an_mode,
+		err = pl->mac_ops->mac_prepare(pl->config, pl->act_link_an_mode,
 					       state->interface);
 		if (err < 0) {
 			phylink_err(pl, "mac_prepare failed: %pe\n",
@@ -1214,7 +1396,7 @@ static void phylink_major_config(struct phylink *pl, bool restart,
 	if (pl->pcs_state == PCS_STATE_STARTING || pcs_changed)
 		phylink_pcs_enable(pl->pcs);
 
-	neg_mode = pl->cur_link_an_mode;
+	neg_mode = pl->act_link_an_mode;
 	if (pl->pcs && pl->pcs->neg_mode)
 		neg_mode = pl->pcs_neg_mode;
 
@@ -1230,13 +1412,20 @@ static void phylink_major_config(struct phylink *pl, bool restart,
 		phylink_pcs_an_restart(pl);
 
 	if (pl->mac_ops->mac_finish) {
-		err = pl->mac_ops->mac_finish(pl->config, pl->cur_link_an_mode,
+		err = pl->mac_ops->mac_finish(pl->config, pl->act_link_an_mode,
 					      state->interface);
 		if (err < 0)
 			phylink_err(pl, "mac_finish failed: %pe\n",
 				    ERR_PTR(err));
 	}
 
+	if (pl->phydev && pl->phy_ib_mode) {
+		err = phy_config_inband(pl->phydev, pl->phy_ib_mode);
+		if (err < 0)
+			phylink_err(pl, "phy_config_inband: %pe\n",
+				    ERR_PTR(err));
+	}
+
 	if (pl->sfp_bus) {
 		rate_kbd = phylink_interface_signal_rate(state->interface);
 		if (rate_kbd)
@@ -1261,17 +1450,16 @@ static int phylink_change_inband_advert(struct phylink *pl)
 		return 0;
 
 	phylink_dbg(pl, "%s: mode=%s/%s adv=%*pb pause=%02x\n", __func__,
-		    phylink_an_mode_str(pl->cur_link_an_mode),
+		    phylink_an_mode_str(pl->req_link_an_mode),
 		    phy_modes(pl->link_config.interface),
 		    __ETHTOOL_LINK_MODE_MASK_NBITS, pl->link_config.advertising,
 		    pl->link_config.pause);
 
 	/* Recompute the PCS neg mode */
-	pl->pcs_neg_mode = phylink_pcs_neg_mode(pl->cur_link_an_mode,
-					pl->link_config.interface,
-					pl->link_config.advertising);
+	phylink_pcs_neg_mode(pl, pl->pcs, pl->link_config.interface,
+			     pl->link_config.advertising);
 
-	neg_mode = pl->cur_link_an_mode;
+	neg_mode = pl->act_link_an_mode;
 	if (pl->pcs->neg_mode)
 		neg_mode = pl->pcs_neg_mode;
 
@@ -1336,7 +1524,7 @@ static void phylink_mac_initial_config(struct phylink *pl, bool force_restart)
 {
 	struct phylink_link_state link_state;
 
-	switch (pl->cur_link_an_mode) {
+	switch (pl->req_link_an_mode) {
 	case MLO_AN_PHY:
 		link_state = pl->phy_state;
 		break;
@@ -1410,14 +1598,14 @@ static void phylink_link_up(struct phylink *pl,
 
 	pl->cur_interface = link_state.interface;
 
-	neg_mode = pl->cur_link_an_mode;
+	neg_mode = pl->act_link_an_mode;
 	if (pl->pcs && pl->pcs->neg_mode)
 		neg_mode = pl->pcs_neg_mode;
 
 	phylink_pcs_link_up(pl->pcs, neg_mode, pl->cur_interface, speed,
 			    duplex);
 
-	pl->mac_ops->mac_link_up(pl->config, pl->phydev, pl->cur_link_an_mode,
+	pl->mac_ops->mac_link_up(pl->config, pl->phydev, pl->act_link_an_mode,
 				 pl->cur_interface, speed, duplex,
 				 !!(link_state.pause & MLO_PAUSE_TX), rx_pause);
 
@@ -1437,7 +1625,7 @@ static void phylink_link_down(struct phylink *pl)
 
 	if (ndev)
 		netif_carrier_off(ndev);
-	pl->mac_ops->mac_link_down(pl->config, pl->cur_link_an_mode,
+	pl->mac_ops->mac_link_down(pl->config, pl->act_link_an_mode,
 				   pl->cur_interface);
 	phylink_info(pl, "Link is Down\n");
 }
@@ -1463,10 +1651,10 @@ static void phylink_resolve(struct work_struct *w)
 	} else if (pl->link_failed) {
 		link_state.link = false;
 		retrigger = true;
-	} else if (pl->cur_link_an_mode == MLO_AN_FIXED) {
+	} else if (pl->act_link_an_mode == MLO_AN_FIXED) {
 		phylink_get_fixed_state(pl, &link_state);
 		mac_config = link_state.link;
-	} else if (pl->cur_link_an_mode == MLO_AN_PHY) {
+	} else if (pl->act_link_an_mode == MLO_AN_PHY) {
 		link_state = pl->phy_state;
 		mac_config = link_state.link;
 	} else {
@@ -1520,7 +1708,7 @@ static void phylink_resolve(struct work_struct *w)
 		}
 	}
 
-	if (pl->cur_link_an_mode != MLO_AN_FIXED)
+	if (pl->act_link_an_mode != MLO_AN_FIXED)
 		phylink_apply_manual_flow(pl, &link_state);
 
 	if (mac_config) {
@@ -1644,7 +1832,7 @@ int phylink_set_fixed_link(struct phylink *pl,
 	pl->link_config.an_complete = 1;
 
 	pl->cfg_link_an_mode = MLO_AN_FIXED;
-	pl->cur_link_an_mode = pl->cfg_link_an_mode;
+	pl->req_link_an_mode = pl->cfg_link_an_mode;
 
 	return 0;
 }
@@ -1732,7 +1920,7 @@ struct phylink *phylink_create(struct phylink_config *config,
 		}
 	}
 
-	pl->cur_link_an_mode = pl->cfg_link_an_mode;
+	pl->req_link_an_mode = pl->cfg_link_an_mode;
 
 	ret = phylink_register_sfp(pl, fwnode);
 	if (ret < 0) {
@@ -2189,7 +2377,7 @@ void phylink_start(struct phylink *pl)
 	ASSERT_RTNL();
 
 	phylink_info(pl, "configuring for %s/%s link mode\n",
-		     phylink_an_mode_str(pl->cur_link_an_mode),
+		     phylink_an_mode_str(pl->req_link_an_mode),
 		     phy_modes(pl->link_config.interface));
 
 	/* Always set the carrier off */
@@ -2474,7 +2662,7 @@ int phylink_ethtool_ksettings_get(struct phylink *pl,
 
 	linkmode_copy(kset->link_modes.supported, pl->supported);
 
-	switch (pl->cur_link_an_mode) {
+	switch (pl->act_link_an_mode) {
 	case MLO_AN_FIXED:
 		/* We are using fixed settings. Report these as the
 		 * current link settings - and note that these also
@@ -2505,6 +2693,26 @@ int phylink_ethtool_ksettings_get(struct phylink *pl,
 }
 EXPORT_SYMBOL_GPL(phylink_ethtool_ksettings_get);
 
+static bool phylink_validate_pcs_inband_autoneg(struct phylink *pl,
+					        phy_interface_t interface,
+						unsigned long *adv)
+{
+	unsigned int inband = phylink_inband_caps(pl, interface);
+	unsigned int mask;
+
+	/* If the PCS doesn't implement inband support, be permissive. */
+	if (!inband)
+		return true;
+
+	if (linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT, adv))
+		mask = LINK_INBAND_ENABLE;
+	else
+		mask = LINK_INBAND_DISABLE;
+
+	/* Check whether the PCS implements the required mode */
+	return !!(inband & mask);
+}
+
 /**
  * phylink_ethtool_ksettings_set() - set the link settings
  * @pl: a pointer to a &struct phylink returned from phylink_create()
@@ -2566,7 +2774,7 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
 		/* If we have a fixed link, refuse to change link parameters.
 		 * If the link parameters match, accept them but do nothing.
 		 */
-		if (pl->cur_link_an_mode == MLO_AN_FIXED) {
+		if (pl->req_link_an_mode == MLO_AN_FIXED) {
 			if (s->speed != pl->link_config.speed ||
 			    s->duplex != pl->link_config.duplex)
 				return -EINVAL;
@@ -2582,7 +2790,7 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
 		 * is our default case) but do not allow the advertisement to
 		 * be changed. If the advertisement matches, simply return.
 		 */
-		if (pl->cur_link_an_mode == MLO_AN_FIXED) {
+		if (pl->req_link_an_mode == MLO_AN_FIXED) {
 			if (!linkmode_equal(config.advertising,
 					    pl->link_config.advertising))
 				return -EINVAL;
@@ -2617,7 +2825,7 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
 		linkmode_copy(support, pl->supported);
 		if (phylink_validate(pl, support, &config)) {
 			phylink_err(pl, "validation of %s/%s with support %*pb failed\n",
-				    phylink_an_mode_str(pl->cur_link_an_mode),
+				    phylink_an_mode_str(pl->req_link_an_mode),
 				    phy_modes(config.interface),
 				    __ETHTOOL_LINK_MODE_MASK_NBITS, support);
 			return -EINVAL;
@@ -2635,6 +2843,13 @@ int phylink_ethtool_ksettings_set(struct phylink *pl,
 	    phylink_is_empty_linkmode(config.advertising))
 		return -EINVAL;
 
+	/* Validate the autonegotiation state. We don't have a PHY in this
+	 * situation, so the PCS is the media-facing entity.
+	 */
+	if (!phylink_validate_pcs_inband_autoneg(pl, config.interface,
+						 config.advertising))
+		return -EINVAL;
+
 	mutex_lock(&pl->state_mutex);
 	pl->link_config.speed = config.speed;
 	pl->link_config.duplex = config.duplex;
@@ -2717,7 +2932,7 @@ int phylink_ethtool_set_pauseparam(struct phylink *pl,
 
 	ASSERT_RTNL();
 
-	if (pl->cur_link_an_mode == MLO_AN_FIXED)
+	if (pl->req_link_an_mode == MLO_AN_FIXED)
 		return -EOPNOTSUPP;
 
 	if (!phylink_test(pl->supported, Pause) &&
@@ -2981,7 +3196,7 @@ static int phylink_mii_read(struct phylink *pl, unsigned int phy_id,
 	struct phylink_link_state state;
 	int val = 0xffff;
 
-	switch (pl->cur_link_an_mode) {
+	switch (pl->act_link_an_mode) {
 	case MLO_AN_FIXED:
 		if (phy_id == 0) {
 			phylink_get_fixed_state(pl, &state);
@@ -3006,7 +3221,7 @@ static int phylink_mii_read(struct phylink *pl, unsigned int phy_id,
 static int phylink_mii_write(struct phylink *pl, unsigned int phy_id,
 			     unsigned int reg, unsigned int val)
 {
-	switch (pl->cur_link_an_mode) {
+	switch (pl->act_link_an_mode) {
 	case MLO_AN_FIXED:
 		break;
 
@@ -3176,10 +3391,11 @@ static phy_interface_t phylink_choose_sfp_interface(struct phylink *pl,
 	return interface;
 }
 
-static void phylink_sfp_set_config(struct phylink *pl, u8 mode,
+static void phylink_sfp_set_config(struct phylink *pl,
 				   unsigned long *supported,
 				   struct phylink_link_state *state)
 {
+	u8 mode = MLO_AN_INBAND;
 	bool changed = false;
 
 	phylink_dbg(pl, "requesting link mode %s/%s with support %*pb\n",
@@ -3196,9 +3412,9 @@ static void phylink_sfp_set_config(struct phylink *pl, u8 mode,
 		changed = true;
 	}
 
-	if (pl->cur_link_an_mode != mode ||
+	if (pl->req_link_an_mode != mode ||
 	    pl->link_config.interface != state->interface) {
-		pl->cur_link_an_mode = mode;
+		pl->req_link_an_mode = mode;
 		pl->link_config.interface = state->interface;
 
 		changed = true;
@@ -3213,8 +3429,7 @@ static void phylink_sfp_set_config(struct phylink *pl, u8 mode,
 		phylink_mac_initial_config(pl, false);
 }
 
-static int phylink_sfp_config_phy(struct phylink *pl, u8 mode,
-				  struct phy_device *phy)
+static int phylink_sfp_config_phy(struct phylink *pl, struct phy_device *phy)
 {
 	__ETHTOOL_DECLARE_LINK_MODE_MASK(support);
 	struct phylink_link_state config;
@@ -3258,7 +3473,7 @@ static int phylink_sfp_config_phy(struct phylink *pl, u8 mode,
 
 	pl->link_port = pl->sfp_port;
 
-	phylink_sfp_set_config(pl, mode, support, &config);
+	phylink_sfp_set_config(pl, support, &config);
 
 	return 0;
 }
@@ -3314,6 +3529,12 @@ static int phylink_sfp_config_optical(struct phylink *pl)
 	phylink_dbg(pl, "optical SFP: chosen %s interface\n",
 		    phy_modes(interface));
 
+	if (!phylink_validate_pcs_inband_autoneg(pl, interface,
+						 config.advertising)) {
+		phylink_err(pl, "autoneg setting not compatible with PCS");
+		return -EINVAL;
+	}
+
 	config.interface = interface;
 
 	/* Ignore errors if we're expecting a PHY to attach later */
@@ -3327,7 +3548,7 @@ static int phylink_sfp_config_optical(struct phylink *pl)
 
 	pl->link_port = pl->sfp_port;
 
-	phylink_sfp_set_config(pl, MLO_AN_INBAND, pl->sfp_support, &config);
+	phylink_sfp_set_config(pl, pl->sfp_support, &config);
 
 	return 0;
 }
@@ -3398,19 +3619,9 @@ static void phylink_sfp_link_up(void *upstream)
 	phylink_enable_and_run_resolve(pl, PHYLINK_DISABLE_LINK);
 }
 
-/* The Broadcom BCM84881 in the Methode DM7052 is unable to provide a SGMII
- * or 802.3z control word, so inband will not work.
- */
-static bool phylink_phy_no_inband(struct phy_device *phy)
-{
-	return phy->is_c45 && phy_id_compare(phy->c45_ids.device_ids[1],
-					     0xae025150, 0xfffffff0);
-}
-
 static int phylink_sfp_connect_phy(void *upstream, struct phy_device *phy)
 {
 	struct phylink *pl = upstream;
-	u8 mode;
 
 	/*
 	 * This is the new way of dealing with flow control for PHYs,
@@ -3421,17 +3632,12 @@ static int phylink_sfp_connect_phy(void *upstream, struct phy_device *phy)
 	 */
 	phy_support_asym_pause(phy);
 
-	if (phylink_phy_no_inband(phy))
-		mode = MLO_AN_PHY;
-	else
-		mode = MLO_AN_INBAND;
-
 	/* Set the PHY's host supported interfaces */
 	phy_interface_and(phy->host_interfaces, phylink_sfp_interfaces,
 			  pl->config->supported_interfaces);
 
 	/* Do the initial configuration */
-	return phylink_sfp_config_phy(pl, mode, phy);
+	return phylink_sfp_config_phy(pl, phy);
 }
 
 static void phylink_sfp_disconnect_phy(void *upstream,
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 563c46205685..61a1bc81f597 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -818,6 +818,24 @@ struct phy_tdr_config {
 #define PHY_PAIR_ALL -1
 
 /**
+ * enum link_inband_signalling - in-band signalling modes that are supported
+ *
+ * @LINK_INBAND_DISABLE: in-band signalling can be disabled
+ * @LINK_INBAND_ENABLE: in-band signalling can be enabled without bypass
+ * @LINK_INBAND_BYPASS: in-band signalling can be enabled with bypass
+ *
+ * The possible and required bits can only be used if the valid bit is set.
+ * If possible is clear, that means inband signalling can not be used.
+ * Required is only valid when possible is set, and means that inband
+ * signalling must be used.
+ */
+enum link_inband_signalling {
+	LINK_INBAND_DISABLE		= BIT(0),
+	LINK_INBAND_ENABLE		= BIT(1),
+	LINK_INBAND_BYPASS		= BIT(2),
+};
+
+/**
  * struct phy_plca_cfg - Configuration of the PLCA (Physical Layer Collision
  * Avoidance) Reconciliation Sublayer.
  *
@@ -957,6 +975,19 @@ struct phy_driver {
 	int (*get_features)(struct phy_device *phydev);
 
 	/**
+	 * @inband_caps: query whether in-band is supported for the given PHY
+	 * interface mode. Returns a bitmask of bits defined by enum
+	 * link_inband_signalling.
+	 */
+	unsigned int (*inband_caps)(struct phy_device *phydev,
+				    phy_interface_t interface);
+
+	/**
+	 * @config_inband: configure in-band mode for the PHY
+	 */
+	int (*config_inband)(struct phy_device *phydev, unsigned int modes);
+
+	/**
 	 * @get_rate_matching: Get the supported type of rate matching for a
 	 * particular phy interface. This is used by phy consumers to determine
 	 * whether to advertise lower-speed modes for that interface. It is
@@ -1818,6 +1849,9 @@ int phy_config_aneg(struct phy_device *phydev);
 int _phy_start_aneg(struct phy_device *phydev);
 int phy_start_aneg(struct phy_device *phydev);
 int phy_aneg_done(struct phy_device *phydev);
+unsigned int phy_inband_caps(struct phy_device *phydev,
+			     phy_interface_t interface);
+int phy_config_inband(struct phy_device *phydev, unsigned int modes);
 int phy_speed_down(struct phy_device *phydev, bool sync);
 int phy_speed_up(struct phy_device *phydev);
 bool phy_check_valid(int speed, int duplex, unsigned long *features);
diff --git a/include/linux/phylink.h b/include/linux/phylink.h
index 5c01048860c4..5462cc6a37dc 100644
--- a/include/linux/phylink.h
+++ b/include/linux/phylink.h
@@ -419,6 +419,7 @@ struct phylink_pcs {
 /**
  * struct phylink_pcs_ops - MAC PCS operations structure.
  * @pcs_validate: validate the link configuration.
+ * @pcs_inband_caps: query inband support for interface mode.
  * @pcs_enable: enable the PCS.
  * @pcs_disable: disable the PCS.
  * @pcs_pre_config: pre-mac_config method (for errata)
@@ -434,6 +435,8 @@ struct phylink_pcs {
 struct phylink_pcs_ops {
 	int (*pcs_validate)(struct phylink_pcs *pcs, unsigned long *supported,
 			    const struct phylink_link_state *state);
+	unsigned int (*pcs_inband_caps)(struct phylink_pcs *pcs,
+					phy_interface_t interface);
 	int (*pcs_enable)(struct phylink_pcs *pcs);
 	void (*pcs_disable)(struct phylink_pcs *pcs);
 	void (*pcs_pre_config)(struct phylink_pcs *pcs,
@@ -471,6 +474,20 @@ int pcs_validate(struct phylink_pcs *pcs, unsigned long *supported,
 		 const struct phylink_link_state *state);
 
 /**
+ * pcs_inband_caps - query PCS in-band capabilities for interface mode.
+ * @pcs: a pointer to a &struct phylink_pcs.
+ * @interface: interface mode to be queried
+ *
+ * Returns zero if it is unknown what in-band signalling is supported by the
+ * PHY (e.g. because the PHY driver doesn't implement the method.) Otherwise,
+ * returns a bit mask of the LINK_INBAND_* values from
+ * &enum link_inband_signalling to describe which inband modes are supported
+ * for this interface mode.
+ */
+unsigned int pcs_inband_caps(struct phylink_pcs *pcs,
+			     phy_interface_t interface);
+
+/**
  * pcs_enable() - enable the PCS.
  * @pcs: a pointer to a &struct phylink_pcs.
  */