[PATCH v5 3/3] usb: gadget: udc: core: Prevent UDC from starting when unbound

From: Badhri Jagan Sridharan
Date: Wed May 31 2023 - 00:02:31 EST

UDC should neither be started nor pulled up unless the gadget driver is
bound. The new flag "allow_start" is now set by gadget_bind_driver()
and cleared by gadget_unbind_driver(). usb_gadget_udc_start_locked()
now checks whether allow_start is set before starting the UDC by
invoking the ->udc_start() callback.

Fixes: fc274c1e9973 ("USB: gadget: Add a new bus for gadgets")
Cc: stable <stable@xxxxxxxxxx>
Signed-off-by: Badhri Jagan Sridharan <badhri@xxxxxxxxxx>
v5 is the first version in this series.
drivers/usb/gadget/udc/core.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index 6ffe5fda8bb7..ac9d6186815d 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -37,6 +37,8 @@ static const struct bus_type gadget_bus_type;
* @vbus: for udcs who care about vbus status, this value is real vbus status;
* for udcs who do not care about vbus status, this value is always true
* @started: the UDC's started state. True if the UDC had started.
+ * @allow_start: Indicates whether UDC is allowed to start. Set/cleared by gadget_(un)bind_driver()
+ * after gadget driver is bound or unbound.
* @connect_lock: protects udc->vbus, udc->started, gadget->connect, gadget->deactivate related
* functions. usb_gadget_connect_locked, usb_gadget_disconnect_locked,
* usb_udc_connect_control_locked, usb_gadget_udc_start_locked, usb_gadget_udc_stop_locked are
@@ -52,6 +54,7 @@ struct usb_udc {
struct list_head list;
bool vbus;
bool started;
+ bool allow_start;
struct work_struct vbus_work;
struct mutex connect_lock;
@@ -1204,6 +1207,9 @@ static inline int usb_gadget_udc_start_locked(struct usb_udc *udc)
if (udc->started) {
dev_err(&udc->dev, "UDC had already started\n");
return -EBUSY;
+ } else if (!udc->allow_start) {
+ dev_err(&udc->dev, "UDC not allowed to start. Is gadget driver bound ?\n");
+ return -EIO;

ret = udc->gadget->ops->udc_start(udc->gadget, udc->driver);
@@ -1590,6 +1596,7 @@ static int gadget_bind_driver(struct device *dev)
goto err_bind;

+ udc->allow_start = true;
ret = usb_gadget_udc_start_locked(udc);
if (ret) {
@@ -1630,6 +1637,7 @@ static void gadget_unbind_driver(struct device *dev)

+ udc->allow_start = false;
if (gadget->irq)