[PATCH 4.14 21/65] usb: core: hub: Improved device recognition on remote wakeup

Greg Kroah-Hartman
2020-01-22T09:38:10Z

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

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

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1164,6 +1164,7 @@ 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);