usb: gadget: add some infracture to register/unregister functions

This patch provides an infrastructure to register & unregister a USB
function. This allows to turn a function into a module and avoid the
'#include "f_.*.c"' magic and we get a clear API / cut between the bare
gadget and its functions.
The concept is simple:
Each function defines the DECLARE_USB_FUNCTION_INIT macro whith an unique
name of the function and two allocation functions.
- one to create an "instance". The instance holds the current configuration
  set. In case there are two usb_configudations with one function there will
  be one instance and two usb_functions
- one to create an "function" from the instance.

The name of the instance is used to automaticaly load the module if it the
instance is not yet available.
The usb_function callbacks are slightly modified and extended:
- usb_get_function()
  creates a struct usb_function inclunding all pointers (bind,
  unbind,…). It uses the "instance" to map its configuration. So we can
  have _two_ struct usb_function, one for each usb_configuration.
- ->unbind()
  Since the struct usb_function was not allocated in ->bind() it should
  not kfree()d here. This function should only reverse what happens in
  ->bind() that is request cleanup and the cleanup of allocated
  descriptors.
- ->free_func()
  a simple kfree() of the struct usb_function

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

1 files changed, 30 insertions, 17 deletions

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 9db000013f5d..4aa0e4652228 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -683,6 +683,31 @@ done:
 	return result;
 }
 
+int usb_add_config_only(struct usb_composite_dev *cdev,
+		struct usb_configuration *config)
+{
+	struct usb_configuration *c;
+
+	if (!config->bConfigurationValue)
+		return -EINVAL;
+
+	/* Prevent duplicate configuration identifiers */
+	list_for_each_entry(c, &cdev->configs, list) {
+		if (c->bConfigurationValue == config->bConfigurationValue)
+			return -EBUSY;
+	}
+
+	config->cdev = cdev;
+	list_add_tail(&config->list, &cdev->configs);
+
+	INIT_LIST_HEAD(&config->functions);
+	config->next_interface_id = 0;
+	memset(config->interface, 0, sizeof(config->interface));
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_add_config_only);
+
 /**
  * usb_add_config() - add a configuration to a device.
  * @cdev: wraps the USB gadget
@@ -703,30 +728,18 @@ int usb_add_config(struct usb_composite_dev *cdev,
 		int (*bind)(struct usb_configuration *))
 {
 	int				status = -EINVAL;
-	struct usb_configuration	*c;
+
+	if (!bind)
+		goto done;
 
 	DBG(cdev, "adding config #%u '%s'/%p\n",
 			config->bConfigurationValue,
 			config->label, config);
 
-	if (!config->bConfigurationValue || !bind)
+	status = usb_add_config_only(cdev, config);
+	if (status)
 		goto done;
 
-	/* Prevent duplicate configuration identifiers */
-	list_for_each_entry(c, &cdev->configs, list) {
-		if (c->bConfigurationValue == config->bConfigurationValue) {
-			status = -EBUSY;
-			goto done;
-		}
-	}
-
-	config->cdev = cdev;
-	list_add_tail(&config->list, &cdev->configs);
-
-	INIT_LIST_HEAD(&config->functions);
-	config->next_interface_id = 0;
-	memset(config->interface, 0, sizeof(config->interface));
-
 	status = bind(config);
 	if (status < 0) {
 		while (!list_empty(&config->functions)) {