usb: gadget: udc: renesas_usb3: add a safety connection way for forced_b_device

This patch adds a safety connection way for "forced_b_device" with
"workaround_for_vbus" like below:

< Example for R-Car E3 Ebisu >
 # modprobe <any usb gadget driver>
 # echo 1 > /sys/kernel/debug/ee020000.usb/b_device
 (connect a usb cable to host side.)
 # echo 2 > /sys/kernel/debug/ee020000.usb/b_device

Previous code should have connected a usb cable before the "b_device"
is set to 1 on the Ebisu board. However, if xHCI driver on the board
is probed, it causes some troubles:
 - Conflicts USB VBUS/signals between the board and another host.
 - "Cannot enable. Maybe the USB cable is bad?" might happen on
   both the board and another host with a usb hub.
 - Cannot enumerate a usb gadget correctly because an interruption
   of VBUS change happens unexpectedly.
Reported-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/renesas_usb3.c

@@ -358,6 +358,7 @@ struct renesas_usb3 {
 	bool extcon_host;		/* check id and set EXTCON_USB_HOST */
 	bool extcon_usb;		/* check vbus and set EXTCON_USB */
 	bool forced_b_device;
+	bool start_to_connect;
 };
 
 #define gadget_to_renesas_usb3(_gadget)	\
@@ -476,6 +477,7 @@ static void usb3_init_axi_bridge(struct renesas_usb3 *usb3)
 static void usb3_init_epc_registers(struct renesas_usb3 *usb3)
 {
 	usb3_write(usb3, ~0, USB3_USB_INT_STA_1);
+	if (!usb3->workaround_for_vbus)
 		usb3_enable_irq_1(usb3, USB_INT_1_VBUS_CNG);
 }
 
@@ -700,8 +702,7 @@ static void usb3_mode_config(struct renesas_usb3 *usb3, bool host, bool a_dev)
 	usb3_set_mode_by_role_sw(usb3, host);
 	usb3_vbus_out(usb3, a_dev);
 	/* for A-Peripheral or forced B-device mode */
-	if ((!host && a_dev) ||
-	    (usb3->workaround_for_vbus && usb3->forced_b_device))
+	if ((!host && a_dev) || usb3->start_to_connect)
 		usb3_connect(usb3);
 	spin_unlock_irqrestore(&usb3->lock, flags);
 }
@@ -2432,7 +2433,11 @@ static ssize_t renesas_usb3_b_device_write(struct file *file,
 	if (copy_from_user(&buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
 		return -EFAULT;
 
-	if (!strncmp(buf, "1", 1))
+	usb3->start_to_connect = false;
+	if (usb3->workaround_for_vbus && usb3->forced_b_device &&
+	    !strncmp(buf, "2", 1))
+		usb3->start_to_connect = true;
+	else if (!strncmp(buf, "1", 1))
 		usb3->forced_b_device = true;
 	else
 		usb3->forced_b_device = false;
@@ -2440,7 +2445,7 @@ static ssize_t renesas_usb3_b_device_write(struct file *file,
 	if (usb3->workaround_for_vbus)
 		usb3_disconnect(usb3);
 
-	/* Let this driver call usb3_connect() anyway */
+	/* Let this driver call usb3_connect() if needed */
 	usb3_check_id(usb3);
 
 	return count;