linux-kernel - [PATCH 4.9 64/97] usb: core: hub: Improved device recognition on remote wakeup

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Message-Id: <20200122092806.651629548@linuxfoundation.org>
Date:   Wed, 22 Jan 2020 10:29:08 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Keiya Nobuta <nobuta.keiya@...itsu.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: [PATCH 4.9 64/97] usb: core: hub: Improved device recognition on remote wakeup

From: Keiya Nobuta <nobuta.keiya@...itsu.com>

commit 9c06ac4c83df6d6fbdbf7488fbad822b4002ba19 upstream.

If hub_activate() is called before D+ has stabilized after remote
wakeup, the following situation might occur:

         __      ___________________
        /  \    /
D+   __/    \__/

Hub  _______________________________
          |  ^   ^           ^
          |  |   |           |
Host _____v__|___|___________|______
          |  |   |           |
          |  |   |           \-- Interrupt Transfer (*3)
          |  |    \-- ClearPortFeature (*2)
          |   \-- GetPortStatus (*1)
          \-- Host detects remote wakeup

- D+ goes high, Host starts running by remote wakeup
- D+ is not stable, goes low
- Host requests GetPortStatus at (*1) and gets the following hub status:
  - Current Connect Status bit is 0
  - Connect Status Change bit is 1
- D+ stabilizes, goes high
- Host requests ClearPortFeature and thus Connect Status Change bit is
  cleared at (*2)
- After waiting 100 ms, Host starts the Interrupt Transfer at (*3)
- Since the Connect Status Change bit is 0, Hub returns NAK.

In this case, port_event() is not called in hub_event() and Host cannot
recognize device. To solve this issue, flag change_bits even if only
Connect Status Change bit is 1 when got in the first GetPortStatus.

This issue occurs rarely because it only if D+ changes during a very
short time between GetPortStatus and ClearPortFeature. However, it is
fatal if it occurs in embedded system.

Signed-off-by: Keiya Nobuta <nobuta.keiya@...itsu.com>
Cc: stable <stable@...r.kernel.org>
Acked-by: Alan Stern <stern@...land.harvard.edu>
Link: https://lore.kernel.org/r/20200109051448.28150-1-nobuta.keiya@fujitsu.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1162,6 +1162,7 @@ static void hub_activate(struct usb_hub
 			 * PORT_OVER_CURRENT is not. So check for any of them.
 			 */
 			if (udev || (portstatus & USB_PORT_STAT_CONNECTION) ||
+			    (portchange & USB_PORT_STAT_C_CONNECTION) ||
 			    (portstatus & USB_PORT_STAT_OVERCURRENT) ||
 			    (portchange & USB_PORT_STAT_C_OVERCURRENT))
 				set_bit(port1, hub->change_bits);