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@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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