usb: isp1760: fix possible deadlock in isp1760_udc_irq

Use spin_{un,}lock_irq{save,restore} in isp1760_udc_{start,stop} to
prevent following potentially deadlock scenario between
isp1760_udc_{start,stop} and isp1760_udc_irq :

=================================
[ INFO: inconsistent lock state ]
4.0.0-rc2-00004-gf7bb2ef60173 #51 Not tainted
---------------------------------
inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
in:imklog/2118 [HC1[1]:SC0[0]:HE0:SE1] takes:
 (&(&udc->lock)->rlock){?.+...}, at: [<c0397a93>] isp1760_udc_irq+0x367/0x9dc
{HARDIRQ-ON-W} state was registered at:
  [<c05135b3>] _raw_spin_lock+0x23/0x30
  [<c0396b87>] isp1760_udc_start+0x23/0xf8
  [<c039dc21>] udc_bind_to_driver+0x71/0xb0
  [<c039de4f>] usb_gadget_probe_driver+0x53/0x9c
  [<bf80d0df>] usb_composite_probe+0x8a/0xa4 [libcomposite]
  [<bf8311a7>] 0xbf8311a7
  [<c00088c5>] do_one_initcall+0x8d/0x17c
  [<c050b92d>] do_init_module+0x49/0x148
  [<c0087323>] load_module+0xb7f/0xbc4
  [<c0087471>] SyS_finit_module+0x51/0x74
  [<c000d8c1>] ret_fast_syscall+0x1/0x68
irq event stamp: 4966
hardirqs last  enabled at (4965): [<c05137df>] _raw_spin_unlock_irq+0x1f/0x24
hardirqs last disabled at (4966): [<c00110b3>] __irq_svc+0x33/0x64
softirqs last  enabled at (4458): [<c0023475>] __do_softirq+0x23d/0x2d0
softirqs last disabled at (4389): [<c002380b>] irq_exit+0xef/0x15c

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(&udc->lock)->rlock);
  <Interrupt>
    lock(&(&udc->lock)->rlock);

 *** DEADLOCK ***

1 lock held by in:imklog/2118:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<c010a101>] __fdget_pos+0x31/0x34
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/isp1760/isp1760-udc.c

@@ -1191,6 +1191,7 @@ static int isp1760_udc_start(struct usb_gadget *gadget,
 			     struct usb_gadget_driver *driver)
 {
 	struct isp1760_udc *udc = gadget_to_udc(gadget);
+	unsigned long flags;
 
 	/* The hardware doesn't support low speed. */
 	if (driver->max_speed < USB_SPEED_FULL) {
@@ -1198,7 +1199,7 @@ static int isp1760_udc_start(struct usb_gadget *gadget,
 		return -EINVAL;
 	}
 
-	spin_lock(&udc->lock);
+	spin_lock_irqsave(&udc->lock, flags);
 
 	if (udc->driver) {
 		dev_err(udc->isp->dev, "UDC already has a gadget driver\n");
@@ -1208,7 +1209,7 @@ static int isp1760_udc_start(struct usb_gadget *gadget,
 
 	udc->driver = driver;
 
-	spin_unlock(&udc->lock);
+	spin_unlock_irqrestore(&udc->lock, flags);
 
 	dev_dbg(udc->isp->dev, "starting UDC with driver %s\n",
 		driver->function);
@@ -1232,6 +1233,7 @@ static int isp1760_udc_start(struct usb_gadget *gadget,
 static int isp1760_udc_stop(struct usb_gadget *gadget)
 {
 	struct isp1760_udc *udc = gadget_to_udc(gadget);
+	unsigned long flags;
 
 	dev_dbg(udc->isp->dev, "%s\n", __func__);
 
@@ -1239,9 +1241,9 @@ static int isp1760_udc_stop(struct usb_gadget *gadget)
 
 	isp1760_udc_write(udc, DC_MODE, 0);
 
-	spin_lock(&udc->lock);
+	spin_lock_irqsave(&udc->lock, flags);
 	udc->driver = NULL;
-	spin_unlock(&udc->lock);
+	spin_unlock_irqrestore(&udc->lock, flags);
 
 	return 0;
 }