Fix a potential soft lockup in the AT91 UDC driver by ensuring that the
UDC clock is enabled inside the interrupt handler. If the UDC clock is
not enabled then the UDC registers cannot be written to and the
interrupt cannot be cleared or masked.

Note that this patch (and other parts of the existing AT91 UDC driver)
is potentially racy for preempt-rt kernels, but is okay for mainline.

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: Harro Haan <hrhaan@gmail.com>
Tested-by: Remy Bohmer <linux@bohmer.net>
Cc: Andrew Victor <avictor.za@gmail.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>

----

diff --git a/drivers/usb/gadget/at91_udc.c b/drivers/usb/gadget/at91_udc.c
index c4997e9..5ba8319 100644
--- a/drivers/usb/gadget/at91_udc.c
+++ b/drivers/usb/gadget/at91_udc.c
@@ -1370,6 +1370,12 @@ static irqreturn_t at91_udc_irq (int irq, void *_udc)
 {
 	struct at91_udc		*udc = _udc;
 	u32			rescans = 5;
+	int			disable_clock = 0;
+
+	if (!udc->clocked) {
+		clk_on(udc);
+		disable_clock = 1;
+	}
 
 	while (rescans--) {
 		u32 status;
@@ -1458,6 +1464,9 @@ static irqreturn_t at91_udc_irq (int irq, void *_udc)
 		}
 	}
 
+	if (disable_clock)
+		clk_off(udc);
+
 	return IRQ_HANDLED;
 }
 

--