[PATCH v3] usb: gadget: provide interface for legacy gadgets to get UDC name

[Marek Szyprowski <m.szyprowski@samsung.com>]

Since commit 855ed04a3758b205e84b269f92d26ab36ed8e2f7 ("usb: gadget:
udc-core: independent registration of gadgets and gadget drivers") gadget
drivers can not assume that UDC drivers are already available on their
initialization. This broke the HACK, which was used in gadgetfs driver,
to get UDC controller name. This patch removes this hack and replaces it
by additional function in the UDC core (which is usefully only for legacy
drivers, please don't use it in the new code).

Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Vegard Nossum <vegard.nossum@oracle.com>
---
changelog:
v3:
- simplified code a bit

v2: https://lkml.org/lkml/2016/2/8/234
- properly report udc gagdet driver name instead of udc device name

v1: https://lkml.org/lkml/2016/2/8/176
- initial version
---
 drivers/usb/gadget/legacy/inode.c | 28 +++-------------------------
 drivers/usb/gadget/udc/udc-core.c | 30 ++++++++++++++++++++++++++++++
 include/linux/usb/gadget.h        |  1 +
 3 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 87fb0fd..5cdaf01 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1699,28 +1699,6 @@ static struct usb_gadget_driver gadgetfs_driver = {
 };
 
 /*----------------------------------------------------------------------*/
-
-static void gadgetfs_nop(struct usb_gadget *arg) { }
-
-static int gadgetfs_probe(struct usb_gadget *gadget,
-		struct usb_gadget_driver *driver)
-{
-	CHIP = gadget->name;
-	return -EISNAM;
-}
-
-static struct usb_gadget_driver probe_driver = {
-	.max_speed	= USB_SPEED_HIGH,
-	.bind		= gadgetfs_probe,
-	.unbind		= gadgetfs_nop,
-	.setup		= (void *)gadgetfs_nop,
-	.disconnect	= gadgetfs_nop,
-	.driver	= {
-		.name		= "nop",
-	},
-};
-
-
 /* DEVICE INITIALIZATION
  *
  *     fd = open ("/dev/gadget/$CHIP", O_RDWR)
@@ -1971,9 +1949,7 @@ gadgetfs_fill_super (struct super_block *sb, void *opts, int silent)
 	if (the_device)
 		return -ESRCH;
 
-	/* fake probe to determine $CHIP */
-	CHIP = NULL;
-	usb_gadget_probe_driver(&probe_driver);
+	CHIP = usb_get_gadget_udc_name();
 	if (!CHIP)
 		return -ENODEV;
 
@@ -2034,6 +2010,8 @@ gadgetfs_kill_sb (struct super_block *sb)
 		put_dev (the_device);
 		the_device = NULL;
 	}
+	kfree(CHIP);
+	CHIP = NULL;
 }
 
 /*----------------------------------------------------------------------*/
diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
index fd73a3e..fd30242 100644
--- a/drivers/usb/gadget/udc/udc-core.c
+++ b/drivers/usb/gadget/udc/udc-core.c
@@ -442,6 +442,36 @@ err1:
 EXPORT_SYMBOL_GPL(usb_add_gadget_udc_release);
 
 /**
+ * usb_get_gadget_udc_name - get the name of the first UDC controller
+ * This functions returns the name of the first UDC controller in the system.
+ * Please note that this interface is usefull only for legacy drivers which
+ * assume that there is only one UDC controller in the system and they need to
+ * get its name before initialization. There is no guarantee that the UDC
+ * of the returned name will be still available, when gadget driver registers
+ * itself.
+ *
+ * Returns pointer to string with UDC controller name on success, NULL
+ * otherwise. Caller should kfree() returned string.
+ */
+char *usb_get_gadget_udc_name(void)
+{
+	struct usb_udc *udc;
+	char *name = NULL;
+
+	/* For now we take the first available UDC */
+	mutex_lock(&udc_lock);
+	list_for_each_entry(udc, &udc_list, list) {
+		if (!udc->driver) {
+			name = kstrdup(udc->gadget->name, GFP_KERNEL);
+			break;
+		}
+	}
+	mutex_unlock(&udc_lock);
+	return name;
+}
+EXPORT_SYMBOL_GPL(usb_get_gadget_udc_name);
+
+/**
  * usb_add_gadget_udc - adds a new gadget to the udc class driver list
  * @parent: the parent device to this udc. Usually the controller
  * driver's device.
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index d82d006..547d86d 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -1126,6 +1126,7 @@ extern int usb_add_gadget_udc_release(struct device *parent,
 		struct usb_gadget *gadget, void (*release)(struct device *dev));
 extern int usb_add_gadget_udc(struct device *parent, struct usb_gadget *gadget);
 extern void usb_del_gadget_udc(struct usb_gadget *gadget);
+extern char *usb_get_gadget_udc_name(void);
 
 /*-------------------------------------------------------------------------*/
 
-- 
1.9.2