linux-kernel - [PATCH 3.16 185/245] usb: core: hub: Improved device recognition on remote wakeup

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Date:   Fri, 24 Apr 2020 00:06:52 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Alan Stern" <stern@...land.harvard.edu>,
        "Keiya Nobuta" <nobuta.keiya@...itsu.com>
Subject: [PATCH 3.16 185/245] usb: core: hub: Improved device recognition
 on remote wakeup

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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>
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>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/usb/core/hub.c | 1 +
 1 file changed, 1 insertion(+)

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1125,6 +1125,7 @@ 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);