[PATCH net-next 2/5] net: stmmac: address non-LPI resume failures properly

[Russell King (Oracle)]

The Synopsys Designware GMAC core databook requires all clocks to be
active in order to complete software reset, which we perform during
resume.

However, IEEE 802.3 allows a PHY to stop its clocks when placed in
low-power mode, which happens when the system is suspended and WoL
is not enabled.

As an attempt to work around this, commit 36d18b5664ef ("net: stmmac:
start phylink instance before stmmac_hw_setup()") started phylink
early, but this has the side effect that the mac_link_up() method may
be called before or during the initialisation of GMAC hardware.

We also have the socfpga glue driver directly calling phy_resume()
also as an attempt to work around this.

In a previous commit, phylink_prepare_resume() has been introduced
to give MAC drivers a way to ensure that the PHY is resumed prior to
their initialisation of their MAC hardware. This commit adds the call,
and moves the phylink_resume() call back to where it should be before
the aforementioned commit.

Signed-off-by: Russell King (Oracle) <rmk+kernel at armlinux.org.uk>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index a6a533d8a45b..860f800cd014 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -7936,12 +7936,12 @@ int stmmac_resume(struct device *dev)
 	}
 
 	rtnl_lock();
-	phylink_resume(priv->phylink);
-	if (device_may_wakeup(priv->device) && !priv->plat->pmt)
-		phylink_speed_up(priv->phylink);
-	rtnl_unlock();
 
-	rtnl_lock();
+	/* Prepare the PHY to resume, ensuring that its clocks which are
+	 * necessary for the MAC DMA reset to complete are running
+	 */
+	phylink_prepare_resume(priv->phylink);
+
 	mutex_lock(&priv->lock);
 
 	stmmac_reset_queues_param(priv);
@@ -7959,6 +7959,15 @@ int stmmac_resume(struct device *dev)
 	stmmac_enable_all_dma_irq(priv);
 
 	mutex_unlock(&priv->lock);
+
+	/* phylink_resume() must be called after the hardware has been
+	 * initialised because it may bring the link up immediately in a
+	 * workqueue thread, which will race with initialisation.
+	 */
+	phylink_resume(priv->phylink);
+	if (device_may_wakeup(priv->device) && !priv->plat->pmt)
+		phylink_speed_up(priv->phylink);
+
 	rtnl_unlock();
 
 	netif_device_attach(ndev);
-- 
2.30.2