patch "USB: Check for dropped connection before switching to full speed" added to usb-linus

patch "USB: Check for dropped connection before switching to full speed" added to usb-linus

[gregkh]

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

    USB: Check for dropped connection before switching to full speed

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 94c43b9897abf4ea366ed4dba027494e080c7050 Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Tue, 1 Aug 2017 10:41:56 -0400
Subject: USB: Check for dropped connection before switching to full speed

Some buggy USB disk adapters disconnect and reconnect multiple times
during the enumeration procedure.  This may lead to a device
connecting at full speed instead of high speed, because when the USB
stack sees that a device isn't able to enumerate at high speed, it
tries to hand the connection over to a full-speed companion
controller.

The logic for doing this is careful to check that the device is still
connected.  But this check is inadequate if the device disconnects and
reconnects before the check is done.  The symptom is that a device
works, but much more slowly than it is capable of operating.

The situation was made worse recently by commit 22547c4cc4fe ("usb:
hub: Wait for connection to be reestablished after port reset"), which
increases the delay following a reset before a disconnect is
recognized, thus giving the device more time to reconnect.

This patch makes the check more robust.  If the device was
disconnected at any time during enumeration, we will now skip the
full-speed handover.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Zdenek Kabelac <zkabelac@redhat.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/usb/core/hub.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 6e6797d145dd..822f8c50e423 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -4725,7 +4725,8 @@ hub_power_remaining(struct usb_hub *hub)
 static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
 		u16 portchange)
 {
-	int status, i;
+	int status = -ENODEV;
+	int i;
 	unsigned unit_load;
 	struct usb_device *hdev = hub->hdev;
 	struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
@@ -4929,9 +4930,10 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
 
 done:
 	hub_port_disable(hub, port1, 1);
-	if (hcd->driver->relinquish_port && !hub->hdev->parent)
-		hcd->driver->relinquish_port(hcd, port1);
-
+	if (hcd->driver->relinquish_port && !hub->hdev->parent) {
+		if (status != -ENOTCONN && status != -ENODEV)
+			hcd->driver->relinquish_port(hcd, port1);
+	}
 }
 
 /* Handle physical or logical connection change events.
-- 
2.14.0