[PATCH net v2 1/2] net: phylink: allow stopping a suspended instance

[James Hilliard <james.hilliard1@gmail.com>]

If a network driver's system resume fails before phylink_resume(), the
network device can remain administratively up with phylink suspended.
Closing the interface then needs to terminate that suspended instance.
Calling phylink_resume() merely to make phylink_stop() work is not a safe
substitute: resume reconfigures the MAC and restarts link resolution,
although the driver has not successfully restored the MAC.

This is a missing suspend-to-stop transition, independent of the reason
hardware restoration failed. No MAC recovery policy belongs in phylink;
the driver still decides whether to retry resume or wait for an ordinary
administrative down/up cycle.

Without MAC Wake-on-LAN, phylink_suspend() has already called
phylink_stop(). Leave that stopped instance alone instead of repeating
PHY, SFP and PCS shutdown. With MAC Wake-on-LAN, suspend deliberately
defers mac_link_down() and sets PHYLINK_DISABLE_MAC_WOL. Finish that
deferred link-down, drain resolution work and clear the WoL disable bit
while retaining PHYLINK_DISABLE_STOPPED. Otherwise a subsequent start
cannot resolve the link.

Document that a suspended instance can be stopped directly. This neither
resumes the PHY nor reconfigures or brings up the MAC.

Fixes: f97493657c63 ("net: phylink: add suspend/resume support")
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/net/phy/phylink.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index a1458da8111b..df520d77fded 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -2495,11 +2495,18 @@ EXPORT_SYMBOL_GPL(phylink_start);
  *
  * This will synchronously bring down the link if the link is not already
  * down (in other words, it will trigger a mac_link_down() method call.)
+ * A suspended instance may be stopped without first calling phylink_resume().
+ * In particular, closing a device after a failed resume must not restart the
+ * link or reconfigure the MAC just to finish shutting it down.
  */
 void phylink_stop(struct phylink *pl)
 {
 	ASSERT_RTNL();
 
+	/* phylink_suspend() already stops the link without MAC WoL. */
+	if (test_bit(PHYLINK_DISABLE_STOPPED, &pl->phylink_disable_state))
+		return;
+
 	if (pl->sfp_bus)
 		sfp_upstream_stop(pl->sfp_bus);
 	if (pl->phydev)
@@ -2512,6 +2519,16 @@ void phylink_stop(struct phylink *pl)
 
 	phylink_run_resolve_and_disable(pl, PHYLINK_DISABLE_STOPPED);
 
+	if (test_bit(PHYLINK_DISABLE_MAC_WOL, &pl->phylink_disable_state)) {
+		/* Finish the link-down deferred by MAC WoL, without restarting. */
+		flush_work(&pl->resolve);
+		mutex_lock(&pl->state_mutex);
+		if (pl->suspend_link_up)
+			phylink_link_down(pl);
+		__clear_bit(PHYLINK_DISABLE_MAC_WOL, &pl->phylink_disable_state);
+		mutex_unlock(&pl->state_mutex);
+	}
+
 	pl->pcs_state = PCS_STATE_DOWN;
 
 	phylink_pcs_disable(pl->pcs);

-- 
2.53.0