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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: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Alan Stern 2008-04-28 11:06:28 -04:00 committed by Greg Kroah-Hartman
parent b01b03f3ad
commit 24618b0cd4
1 changed files with 19 additions and 12 deletions
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29
drivers/usb/core/hub.c
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@ -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;
}
}
/* Return now if nothing is connected */
/* 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 debouncing failed or nothing is connected */
if (!(portstatus & USB_PORT_STAT_CONNECTION)) {
/* maybe switch power back on (e.g. root hub was reset) */