linux-kernel - [PATCH] usb: gadget: provide interface for legacy gadgets to get UDC name

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Message-id: <1454929965-19897-1-git-send-email-m.szyprowski@samsung.com>
Date:	Mon, 08 Feb 2016 12:12:45 +0100
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Ruslan Bilovol <ruslan.bilovol@...il.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Chen <peter.chen@...escale.com>,
	Felipe Balbi <balbi@...nel.org>
Subject: [PATCH] usb: gadget: provide interface for legacy gadgets to get UDC
 name

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).

Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
---
Vegard: Could you check if this patch fixes your issue with gadgetfs and NULL
pointer dereference?

Best regards,
Marek Szyprowski
---
 drivers/usb/gadget/legacy/inode.c | 29 ++---------------------------
 drivers/usb/gadget/udc/udc-core.c | 33 +++++++++++++++++++++++++++++++++
 include/linux/usb/gadget.h        |  1 +
 3 files changed, 36 insertions(+), 27 deletions(-)

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 7e179f81d05c..7a62a2f7bc18 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -227,7 +227,7 @@ static void put_ep (struct ep_data *data)
  * implicitly, starting with the driver name and then endpoint names.
  */
 
-static const char *CHIP;
+static char CHIP[32];
 
 /*----------------------------------------------------------------------*/
 
@@ -1697,28 +1697,6 @@ 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)
@@ -1968,10 +1946,7 @@ 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);
-	if (!CHIP)
+	if (usb_get_gadget_udc_name(CHIP, sizeof(CHIP)) != 0)
 		return -ENODEV;
 
 	/* superblock */
diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
index fd73a3ea07c2..eb70051d5949 100644
--- a/drivers/usb/gadget/udc/udc-core.c
+++ b/drivers/usb/gadget/udc/udc-core.c
@@ -442,6 +442,39 @@ err1:
 EXPORT_SYMBOL_GPL(usb_add_gadget_udc_release);
 
 /**
+ * usb_get_gadget_udc_name - get the name of the first UDC controller
+ * @dst_name
+ * @len
+ * 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 zero on success, negative errno otherwise.
+ */
+int usb_get_gadget_udc_name(char *dst_name, int len)
+{
+	struct usb_udc *udc;
+	int ret = -ENODEV;
+
+	mutex_lock(&udc_lock);
+	list_for_each_entry(udc, &udc_list, list) {
+		const char *name = dev_name(&udc->dev);
+		/* For now we take the first one */
+		if (!udc->driver && strlen(name) + 1 <= len) {
+			strcpy(dst_name, name);
+			ret = 0;
+			break;
+		}
+	}
+	mutex_unlock(&udc_lock);
+	return ret;
+}
+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 d82d0068872b..0a8f08302a34 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 int usb_get_gadget_udc_name(char *dst_name, int len);
 
 /*-------------------------------------------------------------------------*/
 
-- 
1.9.2