[PATCH net-next 2/7] net: phy: Allow flagging PHY devices that can't isolate their MII

[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.

Allow flagging these PHYs, and prevent isolating them altogether.

Assume the PHY can isolate by default.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
 drivers/net/phy/phy_device.c | 11 +++++++++++
 include/linux/phy.h          |  1 +
 2 files changed, 12 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index c468e72bef4b..2a3db1043626 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)
+		return !(phydev->drv->flags & PHY_NO_ISOLATE);
+
+	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..f0a8a5459fbe 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -90,6 +90,7 @@ extern const int phy_10gbit_features_array[1];
 #define PHY_RST_AFTER_CLK_EN	0x00000002
 #define PHY_POLL_CABLE_TEST	0x00000004
 #define PHY_ALWAYS_CALL_SUSPEND	0x00000008
+#define PHY_NO_ISOLATE		0x00000010
 #define MDIO_DEVICE_IS_PHY	0x80000000
 
 /**
-- 
2.46.0