net: phy: add support for querying PHY clock stop capability

Add support for querying whether the PHY allows the transmit xMII clock
to be stopped while in LPI mode. This will be used by phylink to pass
to the MAC driver so it can configure the generation of the xMII clock
appropriately.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/E1tYADg-0014Pb-AJ@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Russell King (Oracle)

drivers/net/phy/phy.c

@@ -1703,6 +1703,26 @@ void phy_mac_interrupt(struct phy_device *phydev)
 }
 EXPORT_SYMBOL(phy_mac_interrupt);
 
+/**
+ * phy_eee_tx_clock_stop_capable() - indicate whether the MAC can stop tx clock
+ * @phydev: target phy_device struct
+ *
+ * Indicate whether the MAC can disable the transmit xMII clock while in LPI
+ * state. Returns 1 if the MAC may stop the transmit clock, 0 if the MAC must
+ * not stop the transmit clock, or negative error.
+ */
+int phy_eee_tx_clock_stop_capable(struct phy_device *phydev)
+{
+	int stat1;
+
+	stat1 = phy_read_mmd(phydev, MDIO_MMD_PCS, MDIO_STAT1);
+	if (stat1 < 0)
+		return stat1;
+
+	return !!(stat1 & MDIO_PCS_STAT1_CLKSTOP_CAP);
+}
+EXPORT_SYMBOL_GPL(phy_eee_tx_clock_stop_capable);
+
 /**
  * phy_eee_rx_clock_stop() - configure PHY receive clock in LPI
  * @phydev: target phy_device struct

include/linux/phy.h

@@ -2146,6 +2146,7 @@ int phy_unregister_fixup(const char *bus_id, u32 phy_uid, u32 phy_uid_mask);
 int phy_unregister_fixup_for_id(const char *bus_id);
 int phy_unregister_fixup_for_uid(u32 phy_uid, u32 phy_uid_mask);
 
+int phy_eee_tx_clock_stop_capable(struct phy_device *phydev);
 int phy_eee_rx_clock_stop(struct phy_device *phydev, bool clk_stop_enable);
 int phy_init_eee(struct phy_device *phydev, bool clk_stop_enable);
 int phy_get_eee_err(struct phy_device *phydev);