USB: UDC core: Add udc_async_callbacks gadget op

The Gadget API has a theoretical race when a gadget driver is unbound.
Although the pull-up is turned off before the driver's ->unbind
callback runs, if the USB cable were to be unplugged at just the wrong
moment there would be nothing to prevent the UDC driver from invoking
the ->disconnect callback after the unbind has finished.  In theory,
other asynchronous callbacks could also happen during the time before
the UDC driver's udc_stop routine is called, and the gadget driver
would not be prepared to handle any of them.

We need a way to tell UDC drivers to stop issuing asynchronous (that is,
->suspend, ->resume, ->disconnect, ->reset, or ->setup) callbacks at
some point after the pull-up has been turned off and before the
->unbind callback runs.  This patch adds a new ->udc_async_callbacks
callback to the usb_gadget_ops structure for precisely this purpose,
and it adds the corresponding support to the UDC core.

Later patches in this series add support for udc_async_callbacks to
several UDC drivers.

Acked-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20210520202144.GC1216852@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 8811eb96e5cc..75c7538e350a 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -325,6 +325,7 @@ struct usb_gadget_ops {
 	void	(*udc_set_speed)(struct usb_gadget *, enum usb_device_speed);
 	void	(*udc_set_ssp_rate)(struct usb_gadget *gadget,
 			enum usb_ssp_rate rate);
+	void	(*udc_async_callbacks)(struct usb_gadget *gadget, bool enable);
 	struct usb_ep *(*match_ep)(struct usb_gadget *,
 			struct usb_endpoint_descriptor *,
 			struct usb_ss_ep_comp_descriptor *);