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Commit 24618b0c authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
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USB: debounce before unregistering 



This patch (as1080) makes a significant change to the way khubd
handles port connect-change and enable-change events.  Both types of
event are now debounced, and the debouncing is carried out _before_ an
existing usb_device is unregistered, instead of afterward.

This means that drivers will have to deal with longer runs of errors
when a device is unplugged, but they are supposed to be prepared for
that in any case.

The advantage is that when an enable-change occurs (caused for example
by electromagnetic interference), the debouncing period will provide
time for the cause of the problem to die away.  A simple port reset
(added in a forthcoming patch) will then allow us to recover from the
fault.

Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent b01b03f3

drivers/usb/core/hub.c

+19 −12
Original line number Diff line number Diff line
@@ -2673,7 +2673,8 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1, 
	struct usb_device *hdev = hub->hdev;

	struct device *hub_dev = hub->intfdev;

	struct usb_hcd *hcd = bus_to_hcd(hdev->bus);

	u16 wHubCharacteristics = le16_to_cpu(hub->descriptor->wHubCharacteristics);

	unsigned wHubCharacteristics =

			le16_to_cpu(hub->descriptor->wHubCharacteristics);

	int status, i;



	dev_dbg (hub_dev,
@@ -2685,29 +2686,35 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1, 
		hub->indicator[port1-1] = INDICATOR_AUTO;

	}



	/* Disconnect any existing devices under this port */

	if (hdev->children[port1-1])

		usb_disconnect(&hdev->children[port1-1]);

	clear_bit(port1, hub->change_bits);



#ifdef	CONFIG_USB_OTG

	/* during HNP, don't repeat the debounce */

	if (hdev->bus->is_b_host)

		portchange &= ~USB_PORT_STAT_C_CONNECTION;

		portchange &= ~(USB_PORT_STAT_C_CONNECTION |

				USB_PORT_STAT_C_ENABLE);

#endif



	if (portchange & USB_PORT_STAT_C_CONNECTION) {

	/* Try to use the debounce delay for protection against

	 * port-enable changes caused, for example, by EMI.

	 */

	if (portchange & (USB_PORT_STAT_C_CONNECTION |

				USB_PORT_STAT_C_ENABLE)) {

		status = hub_port_debounce(hub, port1);

		if (status < 0) {

			if (printk_ratelimit())

				dev_err (hub_dev, "connect-debounce failed, "

						"port %d disabled\n", port1);

			goto done;

		}

			portstatus &= ~USB_PORT_STAT_CONNECTION;

		} else {

			portstatus = status;

		}

	}



	/* Disconnect any existing devices under this port */

	if (hdev->children[port1-1])

		usb_disconnect(&hdev->children[port1-1]);

	clear_bit(port1, hub->change_bits);



	/* Return now if nothing is connected */

	/* Return now if debouncing failed or nothing is connected */

	if (!(portstatus & USB_PORT_STAT_CONNECTION)) {



		/* maybe switch power back on (e.g. root hub was reset) */