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>

2 files changed, 31 insertions, 18 deletions

diff --git a/drivers/usb/gadget/Makefile b/drivers/usb/gadget/Makefile
index 8b4acfd92aa3..fef41f5d6e8d 100644
--- a/drivers/usb/gadget/Makefile
+++ b/drivers/usb/gadget/Makefile
@@ -6,7 +6,7 @@ ccflags-$(CONFIG_USB_GADGET_DEBUG) := -DDEBUG
 obj-$(CONFIG_USB_GADGET)        += udc-core.o
 obj-$(CONFIG_USB_LIBCOMPOSITE)  += libcomposite.o
 libcomposite-y                  := usbstring.o config.o epautoconf.o
-libcomposite-y                  += composite.o
+libcomposite-y                  += composite.o functions.o
 obj-$(CONFIG_USB_DUMMY_HCD)     += dummy_hcd.o
 obj-$(CONFIG_USB_NET2272)       += net2272.o
 obj-$(CONFIG_USB_NET2280)       += net2280.o
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)) {