This patch (as1221) changes the way usbcore reinitializes a device
following a reset or a reset-resume. Currently we call
usb_set_interface() for every interface in the active configuration;
this is to put the interface into the same altsetting as before the
reset and to make sure that the host's endpoint state matches the
device's endpoint state.
However, sending a Set-Interface request is a waste of time if an
interface was already in altsetting 0 before the reset, since it is
certainly in altsetting 0 afterward. In addition, many devices can't
handle Set-Interface requests -- they crash when they receive them.
So instead, the patch adds code to check each interface. If the
interface wasn't in altsetting 0 before the reset, we go head with the
Set-Interface request as before. But if it was then we skip sending
the Set-Interface request, and we clear out the host-side endpoint
state by calling usb_disable_interface() followed by
usb_enable_interface().
The patch also adds a couple of new comments to explain what's going
on.
Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
---
Index: usb-2.6/drivers/usb/core/hub.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/hub.c
+++ usb-2.6/drivers/usb/core/hub.c
@@ -3393,10 +3393,10 @@ static int usb_reset_and_verify_device(s
udev->descriptor = descriptor; /* for disconnect() calls */
goto re_enumerate;
}
-
+
+ /* Restore the device's previous configuration */
if (!udev->actconfig)
goto done;
-
ret = usb_control_msg(udev, usb_sndctrlpipe(udev, 0),
USB_REQ_SET_CONFIGURATION, 0,
udev->actconfig->desc.bConfigurationValue, 0,
@@ -3409,16 +3409,25 @@ static int usb_reset_and_verify_device(s
}
usb_set_device_state(udev, USB_STATE_CONFIGURED);
+ /* Put interfaces back into the same altsettings as before.
+ * Don't bother to send the Set-Interface request for interfaces
+ * that were already in altsetting 0; besides being unnecessary,
+ * many devices can't handle it. Instead just reset the host-side
+ * endpoint state.
+ */
for (i = 0; i < udev->actconfig->desc.bNumInterfaces; i++) {
struct usb_interface *intf = udev->actconfig->interface[i];
struct usb_interface_descriptor *desc;
- /* set_interface resets host side toggle even
- * for altsetting zero. the interface may have no driver.
- */
desc = &intf->cur_altsetting->desc;
- ret = usb_set_interface(udev, desc->bInterfaceNumber,
- desc->bAlternateSetting);
+ if (desc->bAlternateSetting == 0) {
+ usb_disable_interface(udev, intf, true);
+ usb_enable_interface(udev, intf, true);
+ ret = 0;
+ } else {
+ ret = usb_set_interface(udev, desc->bInterfaceNumber,
+ desc->bAlternateSetting);
+ }
if (ret < 0) {
dev_err(&udev->dev, "failed to restore interface %d "
"altsetting %d (error=%d)\n",
--
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