patch "USB: hub: Fix handling of connect changes during sleep" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: hub: Fix handling of connect changes during sleep

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 9f952e26295d977dbfc6fedeaf8c4f112c818d37 Mon Sep 17 00:00:00 2001
From: Alan Stern <[email protected]>
Date: Wed, 22 Apr 2020 16:09:51 -0400
Subject: USB: hub: Fix handling of connect changes during sleep

Commit 8099f58f1ecd ("USB: hub: Don't record a connect-change event during reset-resume") wasn't very well conceived. The problem it tried to fix was that if a connect-change event occurred while the system was asleep (such as a device disconnecting itself from the bus when it is suspended and then reconnecting when it resumes) requiring a reset-resume during the system wakeup transition, the hub port's change_bit entry would remain set afterward. This would cause the hub driver to believe another connect-change event had occurred after the reset-resume, which was wrong and would lead the driver to send unnecessary requests to the device (which could interfere with a firmware update).

The commit tried to fix this by not setting the change_bit during the wakeup. But this was the wrong thing to do; it means that when a device is unplugged while the system is asleep, the hub driver doesn't realize anything has happened: The change_bit flag which would tell it to handle the disconnect event is clear.

The commit needs to be reverted and the problem fixed in a different way. Fortunately an alternative solution was noted in the commit's
Changelog: We can continue to set the change_bit entry in hub_activate() but then clear it when a reset-resume occurs. That way the the hub driver will see the change_bit when a device is disconnected but won't see it when the device is still present.

That's what this patch does.

---
 drivers/usb/core/hub.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index 54cd8ef795ec..83549f009ced 100644
@@ -1223,6 +1223,11 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 #ifdef CONFIG_PM
 			udev->reset_resume = 1;
 #endif
+			/* Don't set the change_bits when the device
+			 * was powered off.
+			 */
+			if (test_bit(port1, hub->power_bits))
+				set_bit(port1, hub->change_bits);
 
 		} else {
 			/* The power session is gone; tell hub_wq */

@@ -3088,6 +3093,15 @@ static int check_port_resume_type(struct usb_device *udev,
 		if (portchange & USB_PORT_STAT_C_ENABLE)
 			usb_clear_port_feature(hub->hdev, port1,
 					USB_PORT_FEAT_C_ENABLE);
+
+		/*
+		 * Whatever made this reset-resume necessary may have
+		 * turned on the port1 bit in hub->change_bits.  But after
+		 * a successful reset-resume we want the bit to be clear;
+		 * if it was on it would indicate that something happened
+		 * following the reset-resume.
+		 */
+		clear_bit(port1, hub->change_bits);
 	}
 
 	return status;

2.26.2