[PATCH net] usbnet: smsc95xx: Fix deadlock on runtime resume

[Lukas Wunner <lukas@xxxxxxxxx>]

Commit 05b35e7eb9a1 ("smsc95xx: add phylib support") amended
smsc95xx_resume() to call phy_init_hw().  That function waits for the
device to runtime resume even though it is placed in the runtime resume
path, causing a deadlock.

The problem is that phy_init_hw() calls down to smsc95xx_mdiobus_read(),
which never uses the _nopm variant of usbnet_read_cmd().  Amend it to
autosense that it's called from the runtime resume/suspend path and use
the _nopm variant if so.

Stacktrace for posterity:

  INFO: task kworker/2:1:49 blocked for more than 122 seconds.
  Workqueue: usb_hub_wq hub_event
  schedule
  rpm_resume
  __pm_runtime_resume
  usb_autopm_get_interface
  usbnet_read_cmd
  __smsc95xx_read_reg
  __smsc95xx_phy_wait_not_busy
  __smsc95xx_mdio_read
  smsc95xx_mdiobus_read
  __mdiobus_read
  mdiobus_read
  smsc_phy_reset
  phy_init_hw
  smsc95xx_resume
  usb_resume_interface
  usb_resume_both
  usb_runtime_resume
  __rpm_callback
  rpm_callback
  rpm_resume
  __pm_runtime_resume
  usb_autoresume_device
  hub_event
  process_one_work

Fixes: 05b35e7eb9a1 ("smsc95xx: add phylib support")
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.10+
Cc: Andre Edich <andre.edich@xxxxxxxxxxxxx>
---
 drivers/net/usb/smsc95xx.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index 4ef61f6b85df..82b8feaa5162 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -285,11 +285,21 @@ static void smsc95xx_mdio_write_nopm(struct usbnet *dev, int idx, int regval)
 	__smsc95xx_mdio_write(dev, pdata->phydev->mdio.addr, idx, regval, 1);
 }
 
+static bool smsc95xx_in_pm(struct usbnet *dev)
+{
+#ifdef CONFIG_PM
+	return dev->udev->dev.power.runtime_status == RPM_RESUMING ||
+	       dev->udev->dev.power.runtime_status == RPM_SUSPENDING;
+#else
+	return false;
+#endif
+}
+
 static int smsc95xx_mdiobus_read(struct mii_bus *bus, int phy_id, int idx)
 {
 	struct usbnet *dev = bus->priv;
 
-	return __smsc95xx_mdio_read(dev, phy_id, idx, 0);
+	return __smsc95xx_mdio_read(dev, phy_id, idx, smsc95xx_in_pm(dev));
 }
 
 static int smsc95xx_mdiobus_write(struct mii_bus *bus, int phy_id, int idx,
@@ -297,7 +307,7 @@ static int smsc95xx_mdiobus_write(struct mii_bus *bus, int phy_id, int idx,
 {
 	struct usbnet *dev = bus->priv;
 
-	__smsc95xx_mdio_write(dev, phy_id, idx, regval, 0);
+	__smsc95xx_mdio_write(dev, phy_id, idx, regval, smsc95xx_in_pm(dev));
 	return 0;
 }
 
-- 
2.35.2