Implement charging mode for the android gadget. The g_file/mass_storage module

might not be available so trick the android gadget into an empty configuration for
charging enumeration.

[usb-moded] Charging mode with android gadget
Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>

src/usb_moded-android.c

@@ -81,4 +81,20 @@ void android_init_values(void)
   }
 }
 
+/* Set a charging mode for the android gadget
+ *
+ * @return 0 if successful, 1 on failure
+ */
+int set_android_charging_mode(void)
+{
+   int ret = 0;
+
+   /* disable, set functions to "null", re-enable */
+   write_to_file("/sys/class/android_usb/android0/enable", "0");
+   write_to_file("/sys/class/android_usb/android0/functions", "null");
+   ret = write_to_file("/sys/class/android_usb/android0/enable", "1");
+   if(ret < 0)
+	return(1);
+   else
+	return(ret);
 }

src/usb_moded-android.h

@@ -22,3 +22,4 @@
 
 int android_settings(void);
 void android_init_values(void);
+int set_android_charging_mode(void);

src/usb_moded.c

@@ -247,6 +247,9 @@ void set_usb_mode(const char *mode)
 	set_usb_module(MODULE_MASS_STORAGE);
 	/* MODULE_CHARGING has all the parameters defined, so it will not match the g_file_storage rule in usb_moded_load_module */
 	ret = usb_moded_load_module(MODULE_CHARGING);
+	/* if charging mode setting did not succeed we might be dealing with android */
+	if(ret)
+	  ret = set_android_charging_mode();
 	goto end;
   }
   else if(!strcmp(mode, MODE_ASK) || !strcmp(mode, MODE_CHARGER))