net: phylink: add PHY_F_RXC_ALWAYS_ON to PHY dev flags

Some MAC controllers (e.g. stmmac) require their connected PHY to
continuously provide a receive clock signal. This can cause issues in two
cases:

  1. The clock signal hasn't been started yet by the time the MAC driver
     initializes its hardware. This can make the initialization fail, as in
      the case of the rzn1 GMAC1 driver.
  2. The clock signal is cut during a power saving event. By the time the
     MAC is brought back up, the clock signal is still not active since
     phylink_start hasn't been called yet. This brings us back to case 1.

If a PHY driver reads this flag, it should ensure that the receive clock
signal is started as soon as possible, and that it isn't brought down when
the PHY goes into suspend.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
[rgantois: commit log]
Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20240326-rxc_bugfix-v6-1-24a74e5c761f@bootlin.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phylink.c

@@ -1923,6 +1923,8 @@ static int phylink_bringup_phy(struct phylink *pl, struct phy_device *phy,
 static int phylink_attach_phy(struct phylink *pl, struct phy_device *phy,
 			      phy_interface_t interface)
 {
+	u32 flags = 0;
+
 	if (WARN_ON(pl->cfg_link_an_mode == MLO_AN_FIXED ||
 		    (pl->cfg_link_an_mode == MLO_AN_INBAND &&
 		     phy_interface_mode_is_8023z(interface) && !pl->sfp_bus)))
@@ -1931,7 +1933,10 @@ static int phylink_attach_phy(struct phylink *pl, struct phy_device *phy,
 	if (pl->phydev)
 		return -EBUSY;
 
-	return phy_attach_direct(pl->netdev, phy, 0, interface);
+	if (pl->config->mac_requires_rxc)
+		flags |= PHY_F_RXC_ALWAYS_ON;
+
+	return phy_attach_direct(pl->netdev, phy, flags, interface);
 }
 
 /**
@@ -2034,6 +2039,9 @@ int phylink_fwnode_phy_connect(struct phylink *pl,
 		pl->link_config.interface = pl->link_interface;
 	}
 
+	if (pl->config->mac_requires_rxc)
+		flags |= PHY_F_RXC_ALWAYS_ON;
+
 	ret = phy_attach_direct(pl->netdev, phy_dev, flags,
 				pl->link_interface);
 	phy_device_free(phy_dev);

include/linux/phy.h

@@ -778,6 +778,7 @@ struct phy_device {
 
 /* Generic phy_device::dev_flags */
 #define PHY_F_NO_IRQ		0x80000000
+#define PHY_F_RXC_ALWAYS_ON	0x40000000
 
 static inline struct phy_device *to_phy_device(const struct device *dev)
 {

include/linux/phylink.h

@@ -138,6 +138,9 @@ enum phylink_op_type {
  * @poll_fixed_state: if true, starts link_poll,
  *		      if MAC link is at %MLO_AN_FIXED mode.
  * @mac_managed_pm: if true, indicate the MAC driver is responsible for PHY PM.
+ * @mac_requires_rxc: if true, the MAC always requires a receive clock from PHY.
+ *                    The PHY driver should start the clock signal as soon as
+ *                    possible and avoid stopping it during suspend events.
  * @ovr_an_inband: if true, override PCS to MLO_AN_INBAND
  * @get_fixed_state: callback to execute to determine the fixed link state,
  *		     if MAC link is at %MLO_AN_FIXED mode.
@@ -150,6 +153,7 @@ struct phylink_config {
 	enum phylink_op_type type;
 	bool poll_fixed_state;
 	bool mac_managed_pm;
+	bool mac_requires_rxc;
 	bool ovr_an_inband;
 	void (*get_fixed_state)(struct phylink_config *config,
 				struct phylink_link_state *state);