usb:gadget: Refcount for gadget pullup

This commit fixes the way gadget's pullup method (wrapped at
usb_gadget_connect/disconnect) is called in the udc-core.

The composite driver allows correct driver registration, even when it calls
the usb_gadget_disconnect method (composite driver configuration is defered
for user space - please look into the description of usb_composite_probe at
composite.c - line: 1623)

One such example is the CCG (Configurable Composite Gadget) driver (at
drivers/staging/ccg), which after its registration has no usb descriptor
(i.e. idProduct, idVendor etc.) and functions registered. Those are configured
after writing to /sys/module/g_ccg/parameters/ or /sys/class/ccg_usb/ccg0/.

Unfortunately, the code at 'usb_gadget_probe_driver' method (some code omitted):

	if (udc_is_newstyle(udc)) {
		bind(udc->gadget);
		usb_gadget_udc_start(udc->gadget, driver);
		usb_gadget_connect(udc->gadget);
	}

Explicitly calls the usb_gadget_connect method for this driver. It looks like
the udc-core enables pullup for a driver, which has no functions and no
descriptor filled (those values are feed from userspace).

The USB composite driver API allows correct driver registration with calling
usb_gadget_disconnect method, but as it is now, _ALL_ newstyle usb gadgets are
connected by default. Therefore it violates the composite API.

The solution (at least until the udc-core is reworked) is to add atomic
variable, which helps in balancing the number of called usb_gadget_connect/
disconnect functions.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index f1b0dca60f1..16892ab59c8 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -533,6 +533,7 @@ struct usb_gadget {
 	unsigned			b_hnp_enable:1;
 	unsigned			a_hnp_support:1;
 	unsigned			a_alt_hnp_support:1;
+	atomic_t                        connect_count;
 	const char			*name;
 	struct device			dev;
 	unsigned			out_epnum;
@@ -724,7 +725,11 @@ static inline int usb_gadget_connect(struct usb_gadget *gadget)
 {
 	if (!gadget->ops->pullup)
 		return -EOPNOTSUPP;
-	return gadget->ops->pullup(gadget, 1);
+
+	if (atomic_inc_return(&gadget->connect_count) == 1)
+		return gadget->ops->pullup(gadget, 1);
+
+	return 0;
 }
 
 /**
@@ -746,7 +751,11 @@ static inline int usb_gadget_disconnect(struct usb_gadget *gadget)
 {
 	if (!gadget->ops->pullup)
 		return -EOPNOTSUPP;
-	return gadget->ops->pullup(gadget, 0);
+
+	if (atomic_dec_and_test(&gadget->connect_count))
+		return gadget->ops->pullup(gadget, 0);
+
+	return 0;
 }