net: phylink: add phylink managed wake-on-lan PHY speed control

Some drivers, e.g. stmmac, use the speed_up()/speed_down() APIs to
gain additional power saving during Wake-on-LAN where the PHY is
managing the state.

Add support to phylink for this, which can be enabled by the MAC
driver. Only change the PHY speed if the PHY is configured for
wake-up, but without any wake-up on the MAC side, as MAC side
means changing the configuration once the negotiation has
completed.

Signed-off-by: Russell King (Oracle) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/phy/phylink.c

···
 	return phydev && (pl->config->wol_phy_legacy || phy_can_wakeup(phydev));
 }
 
+static bool phylink_phy_pm_speed_ctrl(struct phylink *pl)
+{
+	return pl->config->wol_phy_speed_ctrl && !pl->wolopts_mac &&
+	       pl->phydev && phy_may_wakeup(pl->phydev);
+}
+
 /**
  * phylink_suspend() - handle a network device suspend event
  * @pl: a pointer to a &struct phylink returned from phylink_create()
···
 	} else {
 		phylink_stop(pl);
 	}
+
+	if (phylink_phy_pm_speed_ctrl(pl))
+		phylink_speed_down(pl, false);
 }
 EXPORT_SYMBOL_GPL(phylink_suspend);
 
···
 void phylink_resume(struct phylink *pl)
 {
 	ASSERT_RTNL();
+
+	if (phylink_phy_pm_speed_ctrl(pl))
+		phylink_speed_up(pl);
 
 	if (test_bit(PHYLINK_DISABLE_MAC_WOL, &pl->phylink_disable_state)) {
 		/* Wake-on-Lan enabled, MAC handling */

include/linux/phylink.h

···
  * @lpi_timer_default: Default EEE LPI timer setting.
  * @eee_enabled_default: If set, EEE will be enabled by phylink at creation time
  * @wol_phy_legacy: Use Wake-on-Lan with PHY even if phy_can_wakeup() is false
+ * @wol_phy_speed_ctrl: Use phy speed control on suspend/resume
  * @wol_mac_support: Bitmask of MAC supported %WAKE_* options
  */
 struct phylink_config {
···
 
 	/* Wake-on-Lan support */
 	bool wol_phy_legacy;
+	bool wol_phy_speed_ctrl;
 	u32 wol_mac_support;
 };