net: phy: add possible interfaces

Add a possible_interfaces member to struct phy_device to indicate which
interfaces a clause 45 PHY may switch between depending on the media.
This must be populated by the PHY driver by the time the .config_init()
method completes according to the PHYs host-side configuration.

For example, the Marvell 88x3310 PHY can switch between 10GBASE-R,
5GBASE-R, 2500BASE-X, and SGMII on the host side depending on the media
side speed, so all these interface modes are set in the
possible_interfaces member.

This allows phylib users (such as phylink) to know in advance which
interface modes to expect, which allows them to appropriately restrict
the advertised link modes according to the capabilities of other parts
of the link.

Tested-by: Luo Jie <quic_luoj@quicinc.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/E1r6VHk-00DDLN-I7@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/phy_device.c

@@ -1246,6 +1246,8 @@ int phy_init_hw(struct phy_device *phydev)
 	if (ret < 0)
 		return ret;
 
+	phy_interface_zero(phydev->possible_interfaces);
+
 	if (phydev->drv->config_init) {
 		ret = phydev->drv->config_init(phydev);
 		if (ret < 0)

include/linux/phy.h

@@ -605,6 +605,8 @@ struct macsec_ops;
  * @irq_rerun: Flag indicating interrupts occurred while PHY was suspended,
  *             requiring a rerun of the interrupt handler after resume
  * @interface: enum phy_interface_t value
+ * @possible_interfaces: bitmap if interface modes that the attached PHY
+ *			 will switch between depending on media speed.
  * @skb: Netlink message for cable diagnostics
  * @nest: Netlink nest used for cable diagnostics
  * @ehdr: nNtlink header for cable diagnostics
@@ -674,6 +676,7 @@ struct phy_device {
 	u32 dev_flags;
 
 	phy_interface_t interface;
+	DECLARE_PHY_INTERFACE_MASK(possible_interfaces);
 
 	/*
 	 * forced speed & duplex (no autoneg)