[PATCH 1/2] usb: hub: use shorter 120ms post resume hold for SS root hubs

[Lovekesh Solanki]

Commit 8f5b7e2bec1c ("usb: hub: fix detection of high tier USB3 devices
behind suspended hubs") holds a runtime PM reference for
USB_SS_PORT_U0_WAKE_TIME (200ms) after every SS hub resume, so
downstream links have time to finish trianing before the hub can
suspend again.

But 200ms is excessive for root hubs since a root hub has no upstream
suspended hub whose wake propagation needs to be accounted for.
The root hub still needs some time for USB3 link training to complete,
And root hubs also default to zero auto suspend delay and get
periodically resumed by userspace USB enumeration opening and
closing their usbfs nodes (adb, libusb).
This extra 200ms hold stretches this resume into a suspend/resume
cycle of roughly once per second, which on idle AMD systems have
been reported to cause system freezes.

Shorten the post resume hold to 120ms only for root hubs but
keep the 200ms for external hubs that the original commit is
intended for.

Reported-by: Mathieu Fluhr <mathieu.fluhr@xxxxxxxxx>
Link: https://lore.kernel.org/all/CAPyJwA_D9qw0T72f8zwM1yKjP+To=maVANbcdsWM7yRmbBxYvw@xxxxxxxxxxxxxx/
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 8f5b7e2bec1c ("usb: hub: fix detection of high tier USB3 devices behind suspended hubs")
Signed-off-by: Lovekesh Solanki <lovekeshsolanki00@xxxxxxxxx>
---
 drivers/usb/core/hub.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 3345b3298daf..e1415ad5f908 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -76,6 +76,12 @@
  */
 #define USB_SS_PORT_U0_WAKE_TIME	200  /* ms */
 
+/*
+ * Root hubs have no upstream hub whose wake propagation needs to be
+ * accounted for, but still needs time for USB3 link training to complete.
+ */
+#define USB_SS_ROOT_HUB_U0_WAKE_TIME 120 /* ms */
+
 /* Protect struct usb_device->state and ->children members
  * Note: Both are also protected by ->dev.sem, except that ->state can
  * change to USB_STATE_NOTATTACHED even when the semaphore isn't held. */
@@ -1358,7 +1364,9 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 
 		queue_delayed_work(system_power_efficient_wq,
 				   &hub->post_resume_work,
-				   msecs_to_jiffies(USB_SS_PORT_U0_WAKE_TIME));
+				   msecs_to_jiffies(hdev->parent ?
+			USB_SS_PORT_U0_WAKE_TIME :
+			USB_SS_ROOT_HUB_U0_WAKE_TIME));
 		return;
 	}
 
-- 
2.55.0