[PATCH net v4 03/15] 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(). Do not repeat PHY, SFP and PCS shutdown. However,
phylink_prepare_resume() may have powered that stopped PHY back up to
provide the receive clock for MAC reset. Suspend it again if WoL
permits, without repeating phy_stop() on a PHY which is already halted.

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.

Also undo PHY speed control performed by phylink_suspend(). As Andrew
Lunn pointed out, phylink_start() does not restore the advertised speeds
that phylink_resume() normally restores. Track suspend-owned speed
control and restore the saved advertisement from either resume or
suspended stop, including when PHY shutdown has already completed.

An explicit driver speed-down request, such as stmmac's close-time power
saving, must remain in effect until its matching speed-up. Restore any
suspend-owned reduction before applying that request, so it cannot save
the reduced advertisement over the original one. The following stop must
not undo the driver's new reduction.

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 | 51 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 1bbcf46c8356..b7d30ca34031 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -78,6 +78,7 @@ struct phylink {
 
 	bool link_failed;
 	bool suspend_link_up;
+	bool suspend_speed_down;
 	bool force_major_config;
 	bool major_config_failed;
 	bool mac_supports_eee_ops;
@@ -2498,6 +2499,14 @@ void phylink_start(struct phylink *pl)
 }
 EXPORT_SYMBOL_GPL(phylink_start);
 
+static void phylink_restore_suspend_speed(struct phylink *pl)
+{
+	if (pl->suspend_speed_down) {
+		phylink_speed_up(pl);
+		pl->suspend_speed_down = false;
+	}
+}
+
 /**
  * phylink_stop() - stop a phylink instance
  * @pl: a pointer to a &struct phylink returned from phylink_create()
@@ -2509,11 +2518,30 @@ 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.
+ * Any PHY advertisement reduced by phylink_suspend() is restored as part
+ * of this transition.
+ * If phylink_prepare_resume() powered up an already stopped PHY, suspend
+ * it again when Wake-on-LAN permits.
  */
 void phylink_stop(struct phylink *pl)
 {
 	ASSERT_RTNL();
 
+	/* Also undo PHY speed control when terminating a suspended instance. */
+	phylink_restore_suspend_speed(pl);
+
+	if (test_bit(PHYLINK_DISABLE_STOPPED, &pl->phylink_disable_state)) {
+		/* A failed MAC resume may have called phylink_prepare_resume()
+		 * and powered the stopped PHY back up to supply its RX clock.
+		 */
+		if (pl->phydev)
+			phy_suspend(pl->phydev);
+		return;
+	}
+
 	if (pl->sfp_bus)
 		sfp_upstream_stop(pl->sfp_bus);
 	if (pl->phydev)
@@ -2526,6 +2554,16 @@ 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);
@@ -2657,8 +2695,10 @@ void phylink_suspend(struct phylink *pl, bool mac_wol)
 		phylink_stop(pl);
 	}
 
-	if (phylink_phy_pm_speed_ctrl(pl))
+	if (phylink_phy_pm_speed_ctrl(pl)) {
 		phylink_speed_down(pl, false);
+		pl->suspend_speed_down = true;
+	}
 }
 EXPORT_SYMBOL_GPL(phylink_suspend);
 
@@ -2698,8 +2738,7 @@ void phylink_resume(struct phylink *pl)
 {
 	ASSERT_RTNL();
 
-	if (phylink_phy_pm_speed_ctrl(pl))
-		phylink_speed_up(pl);
+	phylink_restore_suspend_speed(pl);
 
 	if (test_bit(PHYLINK_DISABLE_MAC_WOL, &pl->phylink_disable_state)) {
 		/* Wake-on-Lan enabled, MAC handling */
@@ -3616,6 +3655,12 @@ int phylink_speed_down(struct phylink *pl, bool sync)
 
 	ASSERT_RTNL();
 
+	/* An explicit request takes over from suspend-time speed control.
+	 * Restore the original advertisement before saving it again, so a
+	 * repeated speed-down cannot replace it with the reduced advertisement.
+	 */
+	phylink_restore_suspend_speed(pl);
+
 	if (!pl->sfp_bus && pl->phydev)
 		ret = phy_speed_down(pl->phydev, sync);
 

-- 
2.53.0