[PATCH net-next V4 1/2] net: phylink: add a function to resume PHY alone to fix resume issue with WoL enabled

[Clark Wang]

Issue we met:
On some platforms, MAC cannot work after resumed from the suspend with WoL
enabled.

The cause of the issue:
1. phylink_resolve() is in a workqueue which will not be executed immediately.
   This is the call sequence:
       phylink_resolve()->phylink_link_up()->pl->mac_ops->mac_link_up()
   For stmmac driver, mac_link_up() will set the correct speed/duplex...
   values which are from link_state.
2. In stmmac_resume(), it will call stmmac_hw_setup() after called the
   phylink_resume(), because MAC need PHY rx_clk to do the reset.
   stmmac_core_init() is called in function stmmac_hw_setup(), which will
   reset the MAC and set the speed/duplex... to default value.
Conclusion: Because phylink_resolve() cannot determine when it is called, it
            cannot be guaranteed to be called after stmmac_core_init().
	    Once stmmac_core_init() is called after phylink_resolve(),
	    the MAC will be misconfigured and cannot be used.

In order to avoid this problem, add a function called phylink_phy_resume()
to resume PHY separately. This eliminates the need to call phylink_resume()
before stmmac_hw_setup().

Add another judgement before called phy_start() in phylink_start(). This way
phy_start() will not be called multiple times when resumes. At the same time,
it may not affect other drivers that do not use phylink_phy_resume().

Signed-off-by: Clark Wang <xiaoning.wang@xxxxxxx>
---
V2 change:
 - add mac_resume_phy_separately flag to struct phylink to mark if the MAC
   driver uses the phylink_phy_resume() first.
V3 change:
 - add brace to avoid ambiguous 'else'
   Reported-by: kernel test robot <lkp@xxxxxxxxx>
V4:
Many thanks to Jakub and Russel for their suggestions, here are the changes for V4.
 - Unify MAC and PHY in comments and subject to uppercase.
 - Add subject of the sentence.
 - Move && to the end of the line
 - Add notice in the comment of function phylink_phy_resume()
---
 drivers/net/phy/phylink.c | 35 +++++++++++++++++++++++++++++++++--
 include/linux/phylink.h   |  1 +
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index ea8fcce5b2d9..0be57e9463d9 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -80,6 +80,8 @@ struct phylink {
 	DECLARE_PHY_INTERFACE_MASK(sfp_interfaces);
 	__ETHTOOL_DECLARE_LINK_MODE_MASK(sfp_support);
 	u8 sfp_port;
+
+	bool mac_resume_phy_separately;
 };
 
 #define phylink_printk(level, pl, fmt, ...) \
@@ -1509,6 +1511,7 @@ struct phylink *phylink_create(struct phylink_config *config,
 		return ERR_PTR(-EINVAL);
 	}
 
+	pl->mac_resume_phy_separately = false;
 	pl->using_mac_select_pcs = using_mac_select_pcs;
 	pl->phy_state.interface = iface;
 	pl->link_interface = iface;
@@ -1942,8 +1945,12 @@ void phylink_start(struct phylink *pl)
 	}
 	if (poll)
 		mod_timer(&pl->link_poll, jiffies + HZ);
-	if (pl->phydev)
-		phy_start(pl->phydev);
+	if (pl->phydev) {
+		if (!pl->mac_resume_phy_separately)
+			phy_start(pl->phydev);
+		else
+			pl->mac_resume_phy_separately = false;
+	}
 	if (pl->sfp_bus)
 		sfp_upstream_start(pl->sfp_bus);
 }
@@ -2023,6 +2030,30 @@ void phylink_suspend(struct phylink *pl, bool mac_wol)
 }
 EXPORT_SYMBOL_GPL(phylink_suspend);
 
+/**
+ * phylink_phy_resume() - resume PHY alone
+ * @pl: a pointer to a &struct phylink returned from phylink_create()
+ *
+ * In the MAC driver using phylink, if the MAC needs the clock of the PHY
+ * when it resumes, it can call this function to resume the PHY separately.
+ * Then proceed to MAC resume operations.
+ * 
+ * Note: This function MUST ONLY be called before calling phylink_start()
+ *       in the MAC resume function.
+ */
+void phylink_phy_resume(struct phylink *pl)
+{
+	ASSERT_RTNL();
+
+	if (!test_bit(PHYLINK_DISABLE_MAC_WOL, &pl->phylink_disable_state) &&
+	    pl->phydev) {
+		phy_start(pl->phydev);
+		pl->mac_resume_phy_separately = true;
+	}
+
+}
+EXPORT_SYMBOL_GPL(phylink_phy_resume);
+
 /**
  * phylink_resume() - handle a network device resume event
  * @pl: a pointer to a &struct phylink returned from phylink_create()
diff --git a/include/linux/phylink.h b/include/linux/phylink.h
index c492c26202b5..6edfab5f754c 100644
--- a/include/linux/phylink.h
+++ b/include/linux/phylink.h
@@ -589,6 +589,7 @@ void phylink_stop(struct phylink *);
 
 void phylink_suspend(struct phylink *pl, bool mac_wol);
 void phylink_resume(struct phylink *pl);
+void phylink_phy_resume(struct phylink *pl);
 
 void phylink_ethtool_get_wol(struct phylink *, struct ethtool_wolinfo *);
 int phylink_ethtool_set_wol(struct phylink *, struct ethtool_wolinfo *);
-- 
2.34.1