USB: gadget: core: create sysfs link between udc and gadget

udc device and gadget device are tightly coupled, yet there's no good
way to corelate the two. Add a sysfs link in udc that points to the
corresponding gadget device.
An example use case: userspace configures a f_midi configfs driver and
bind the udc device, then it tries to locate the corresponding midi
device, which is a child device of the gadget device. The gadget device
that's associated to the udc device has to be identified in order to
index the midi device. Having a sysfs link would make things much
easier.

Signed-off-by: Roy Luo <royluo@google.com>
Link: https://lore.kernel.org/r/20240307030922.3573161-1-royluo@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index 9d4150124fdb82b91dcbddc3e8ee9dc24abee7ba..76d890f9a40fd52228e353d09235a65a282683fc 100644 (file)
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -1424,8 +1424,16 @@ int usb_add_gadget(struct usb_gadget *gadget)
        if (ret)
                goto err_free_id;
 
+       ret = sysfs_create_link(&udc->dev.kobj,
+                               &gadget->dev.kobj, "gadget");
+       if (ret)
+               goto err_del_gadget;
+
        return 0;
 
+ err_del_gadget:
+       device_del(&gadget->dev);
+
  err_free_id:
        ida_free(&gadget_id_numbers, gadget->id_number);
 
@@ -1534,6 +1542,7 @@ void usb_del_gadget(struct usb_gadget *gadget)
        mutex_unlock(&udc_lock);
 
        kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE);
+       sysfs_remove_link(&udc->dev.kobj, "gadget");
        flush_work(&gadget->work);
        device_del(&gadget->dev);
        ida_free(&gadget_id_numbers, gadget->id_number);