[RFC PATCH v3 net-next 4/6] net: phylink: explicitly configure in-band autoneg for PHYs that support it

[Vladimir Oltean <vladimir.oltean@nxp.com>]

Currently Linux has no control over whether a MAC-to-PHY interface uses
in-band signaling or not, even though phylink has the
	managed = "in-band-status";
property which denotes that the MAC expects in-band signaling to be used.

The problem is really that if the in-band signaling is configurable in
both the PHY and the MAC, there is a risk that they are out of sync
unless phylink manages them both. Most if not all in-band autoneg state
machines follow IEEE 802.3 clause 37, which means that they will not
change the operating mode of the SERDES lane from control to data mode
unless in-band AN completed successfully. Therefore traffic will not
work.

It is particularly unpleasant that currently, we assume that PHYs which
have configurable in-band AN come pre-configured from a prior boot stage
such as U-Boot, because once the bootloader changes, all bets are off.

Let's introduce a new PHY driver method for configuring in-band autoneg,
and make phylink be its first user. The main PHY library does not call
phy_config_inband_autoneg, because it does not know what to configure it
to. Presumably, non-phylink drivers can also call phy_config_inband_autoneg
individually.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/phy/phy.c     | 12 ++++++++++++
 drivers/net/phy/phylink.c | 10 ++++++++++
 include/linux/phy.h       |  8 ++++++++
 3 files changed, 30 insertions(+)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index 975ae3595f8f..3adc818db30d 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -763,6 +763,18 @@ int phy_validate_inband_aneg(struct phy_device *phydev,
 }
 EXPORT_SYMBOL_GPL(phy_validate_inband_aneg);
 
+int phy_config_inband_aneg(struct phy_device *phydev, bool enabled)
+{
+	if (!phydev->drv)
+		return -EIO;
+
+	if (!phydev->drv->config_inband_aneg)
+		return -EOPNOTSUPP;
+
+	return phydev->drv->config_inband_aneg(phydev, enabled);
+}
+EXPORT_SYMBOL_GPL(phy_config_inband_aneg);
+
 /**
  * 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 358246775ad1..b86e8f7b6c40 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -955,6 +955,7 @@ static int phylink_bringup_phy(struct phylink *pl, struct phy_device *phy,
 {
 	struct phylink_link_state config;
 	__ETHTOOL_DECLARE_LINK_MODE_MASK(supported);
+	bool use_inband;
 	char *irq_str;
 	int ret;
 
@@ -994,6 +995,15 @@ static int phylink_bringup_phy(struct phylink *pl, struct phy_device *phy,
 		return ret;
 	}
 
+	use_inband = phylink_autoneg_inband(pl->cur_link_an_mode);
+
+	ret = phy_config_inband_aneg(phy, use_inband);
+	if (ret && ret != -EOPNOTSUPP) {
+		phylink_warn(pl, "failed to configure PHY in-band autoneg: %pe\n",
+			     ERR_PTR(ret));
+		return ret;
+	}
+
 	phy->phylink = pl;
 	phy->phy_link_change = phylink_phy_change;
 
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 4ac876f988ca..c81c6554d564 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -781,6 +781,13 @@ struct phy_driver {
 	int (*validate_inband_aneg)(struct phy_device *phydev,
 				    phy_interface_t interface);
 
+	/**
+	 * @config_inband_aneg: Enable or disable in-band auto-negotiation for
+	 * the system-side interface if the PHY operates in a mode that
+	 * requires it: (Q)SGMII, USXGMII, 1000Base-X, etc.
+	 */
+	int (*config_inband_aneg)(struct phy_device *phydev, bool enabled);
+
 	/** @aneg_done: Determines the auto negotiation result */
 	int (*aneg_done)(struct phy_device *phydev);
 
@@ -1474,6 +1481,7 @@ int phy_config_aneg(struct phy_device *phydev);
 int phy_start_aneg(struct phy_device *phydev);
 int phy_validate_inband_aneg(struct phy_device *phydev,
 			     phy_interface_t interface);
+int phy_config_inband_aneg(struct phy_device *phydev, bool enabled);
 int phy_aneg_done(struct phy_device *phydev);
 int phy_speed_down(struct phy_device *phydev, bool sync);
 int phy_speed_up(struct phy_device *phydev);
-- 
2.25.1