[RFC PATCH net-next 1/8] phy: introduce the phy_check_cdr_lock() function

[Vladimir Oltean]

Some modules, like the MTIP AN/LT block used as a copper backplane PHY
driver, need this extra information from the SerDes PHY as another
source of "link up" information.

Namely, at 25Gbps, the PCS does not have a MDIO_CTRL1_LPOWER bit
implemented in its MDIO_MMD_PCS:MDIO_CTRL1 register, so a phy_suspend()
procedure will not power down the link, and will not cause a link drop
event on the link partner.

By implementing the networking phy_suspend() as phy_power_off() in the
SerDes and introducing phy_check_cdr_lock() as a link indication, we are
able to detect that condition and signal it to upper layers of the
network stack.

Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
 drivers/phy/phy-core.c  | 18 ++++++++++++++++++
 include/linux/phy/phy.h | 22 ++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/phy/phy-core.c b/drivers/phy/phy-core.c
index 96a0b1e111f3..e611ebe993c7 100644
--- a/drivers/phy/phy-core.c
+++ b/drivers/phy/phy-core.c
@@ -553,6 +553,24 @@ int phy_validate(struct phy *phy, enum phy_mode mode, int submode,
 }
 EXPORT_SYMBOL_GPL(phy_validate);
 
+int phy_check_cdr_lock(struct phy *phy, bool *cdr_locked)
+{
+	int ret;
+
+	if (!phy)
+		return -EINVAL;
+
+	if (!phy->ops->check_cdr_lock)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&phy->mutex);
+	ret = phy->ops->check_cdr_lock(phy, cdr_locked);
+	mutex_unlock(&phy->mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(phy_check_cdr_lock);
+
 /**
  * _of_phy_get() - lookup and obtain a reference to a phy by phandle
  * @np: device_node for which to get the phy
diff --git a/include/linux/phy/phy.h b/include/linux/phy/phy.h
index f6d607ef0e80..456d21c67e4f 100644
--- a/include/linux/phy/phy.h
+++ b/include/linux/phy/phy.h
@@ -122,6 +122,19 @@ struct phy_ops {
 			    union phy_configure_opts *opts);
 	int	(*reset)(struct phy *phy);
 	int	(*calibrate)(struct phy *phy);
+
+	/**
+	 * @check_cdr_lock:
+	 *
+	 * Optional.
+	 *
+	 * Check that the CDR (Clock and Data Recovery) logic has locked onto
+	 * bit transitions in the RX stream.
+	 *
+	 * Returns: 0 if the operation was successful, negative error code
+	 * otherwise.
+	 */
+	int	(*check_cdr_lock)(struct phy *phy, bool *cdr_locked);
 	void	(*release)(struct phy *phy);
 	struct module *owner;
 };
@@ -236,6 +249,7 @@ int phy_set_speed(struct phy *phy, int speed);
 int phy_configure(struct phy *phy, union phy_configure_opts *opts);
 int phy_validate(struct phy *phy, enum phy_mode mode, int submode,
 		 union phy_configure_opts *opts);
+int phy_check_cdr_lock(struct phy *phy, bool *cdr_locked);
 
 static inline enum phy_mode phy_get_mode(struct phy *phy)
 {
@@ -414,6 +428,14 @@ static inline int phy_validate(struct phy *phy, enum phy_mode mode, int submode,
 	return -ENOSYS;
 }
 
+static inline int phy_check_cdr_lock(struct phy *phy, bool *cdr_locked)
+{
+	if (!phy)
+		return 0;
+
+	return -ENOSYS;
+}
+
 static inline int phy_get_bus_width(struct phy *phy)
 {
 	return -ENOSYS;
-- 
2.34.1