[PATCH net-next v2 3/9] net: phy: Allow PHY drivers to report isolation support

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

Some PHYs have malfunctionning isolation modes, where the MII lines
aren't correctly set in high-impedance, potentially interfering with the
MII bus in unexpected ways. Some other PHYs simply don't support it.

The isolation support may depend on the interface mode being used, so
introduce a new driver callback to report the isolation support in the
current PHY configuration.

As some PHYs just never support isolation, introduce a genphy helper
that can be used for strictly non-isolating PHYs.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
V2 : Moved from flag to callback, introduced genphy helper

 drivers/net/phy/phy_device.c | 11 +++++++++++
 include/linux/phy.h          | 19 +++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index a0d8ff995024..9294b73c391a 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -2127,6 +2127,14 @@ int phy_loopback(struct phy_device *phydev, bool enable)
 }
 EXPORT_SYMBOL(phy_loopback);
 
+static bool phy_can_isolate(struct phy_device *phydev)
+{
+	if (phydev->drv && phydev->drv->can_isolate)
+		return phydev->drv->can_isolate(phydev);
+
+	return true;
+}
+
 int phy_isolate(struct phy_device *phydev, bool enable)
 {
 	int ret = 0;
@@ -2134,6 +2142,9 @@ int phy_isolate(struct phy_device *phydev, bool enable)
 	if (!phydev->drv)
 		return -EIO;
 
+	if (!phy_can_isolate(phydev))
+		return -EOPNOTSUPP;
+
 	mutex_lock(&phydev->lock);
 
 	if (enable && phydev->isolated) {
diff --git a/include/linux/phy.h b/include/linux/phy.h
index ae33919aa0f5..e43f7169c57d 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -1192,6 +1192,19 @@ struct phy_driver {
 	 */
 	int (*led_polarity_set)(struct phy_device *dev, int index,
 				unsigned long modes);
+
+	/**
+	 * @can_isolate: Query the PHY isolation capability
+	 * @dev: PHY device to query
+	 *
+	 * Although PHY isolation is part of 802.3, not all PHYs support that
+	 * feature. Some PHYs can only support isolation when using a specific
+	 * phy_interface_mode, and some don't support it at all.
+	 *
+	 * Returns true if the PHY can isolate in its current configuration,
+	 * false otherwise.
+	 */
+	bool (*can_isolate)(struct phy_device *dev);
 };
 #define to_phy_driver(d) container_of_const(to_mdio_common_driver(d),		\
 				      struct phy_driver, mdiodrv)
@@ -1910,6 +1923,12 @@ static inline int genphy_no_config_intr(struct phy_device *phydev)
 {
 	return 0;
 }
+
+static inline bool genphy_no_isolate(struct phy_device *phydev)
+{
+	return false;
+}
+
 int genphy_read_mmd_unsupported(struct phy_device *phdev, int devad,
 				u16 regnum);
 int genphy_write_mmd_unsupported(struct phy_device *phdev, int devnum,
-- 
2.46.1