USB: gadget: Add a new bus for gadgets

This patch adds a "gadget" bus and uses it for registering gadgets and
their drivers.  From now on, bindings will be managed by the driver
core rather than through ad-hoc manipulations in the UDC core.

As part of this change, the driver_pending_list is removed.  The UDC
core won't need to keep track of unbound drivers for later binding,
because the driver core handles all of that for us.

However, we do need one new feature: a way to prevent gadget drivers
from being bound to more than one gadget at a time.  The existing code
does this automatically, but the driver core doesn't -- it's perfectly
happy to bind a single driver to all the matching devices on the bus.
The patch adds a new bitflag to the usb_gadget_driver structure for
this purpose.

A nice side effect of this change is a reduction in the total lines of
code, since now the driver core will do part of the work that the UDC
used to do.

A possible future patch could add udc devices to the gadget bus, say
as a separate device type.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/YmSpdxaDNeC2BBOf@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 9 deletions

diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 5830b8a903da..cf7af8a0a6e9 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -664,9 +664,9 @@ static inline int usb_gadget_check_config(struct usb_gadget *gadget)
  * @driver: Driver model state for this driver.
  * @udc_name: A name of UDC this driver should be bound to. If udc_name is NULL,
  *	this driver will be bound to any available UDC.
- * @pending: UDC core private data used for deferred probe of this driver.
- * @match_existing_only: If udc is not found, return an error and don't add this
- *      gadget driver to list of pending driver
+ * @match_existing_only: If udc is not found, return an error and fail
+ *	the driver registration
+ * @is_bound: Allow a driver to be bound to only one gadget
  *
  * Devices are disabled till a gadget driver successfully bind()s, which
  * means the driver will handle setup() requests needed to enumerate (and
@@ -729,8 +729,8 @@ struct usb_gadget_driver {
 	struct device_driver	driver;
 
 	char			*udc_name;
-	struct list_head	pending;
 	unsigned                match_existing_only:1;
+	bool			is_bound:1;
 };
 
 
@@ -740,22 +740,30 @@ struct usb_gadget_driver {
 /* driver modules register and unregister, as usual.
  * these calls must be made in a context that can sleep.
  *
- * these will usually be implemented directly by the hardware-dependent
- * usb bus interface driver, which will only support a single driver.
+ * A gadget driver can be bound to only one gadget at a time.
  */
 
 /**
- * usb_gadget_register_driver - register a gadget driver
+ * usb_gadget_register_driver_owner - register a gadget driver
  * @driver: the driver being registered
+ * @owner: the driver module
+ * @mod_name: the driver module's build name
  * Context: can sleep
  *
  * Call this in your gadget driver's module initialization function,
- * to tell the underlying usb controller driver about your driver.
+ * to tell the underlying UDC controller driver about your driver.
  * The @bind() function will be called to bind it to a gadget before this
  * registration call returns.  It's expected that the @bind() function will
  * be in init sections.
+ *
+ * Use the macro defined below instead of calling this directly.
  */
-int usb_gadget_register_driver(struct usb_gadget_driver *driver);
+int usb_gadget_register_driver_owner(struct usb_gadget_driver *driver,
+		struct module *owner, const char *mod_name);
+
+/* use a define to avoid include chaining to get THIS_MODULE & friends */
+#define usb_gadget_register_driver(driver) \
+	usb_gadget_register_driver_owner(driver, THIS_MODULE, KBUILD_MODNAME)
 
 /**
  * usb_gadget_unregister_driver - unregister a gadget driver