USB: ohci-exynos: initialize registers pointer earlier

In the former code, we have a race condition between the first interrupt
and the regs field initilization in the usb_hcd structure.
If the OHCI irq fires before hcd->regs is set, we are getting a null
pointer dereference in ohci_irq.

When calling usb_add_hcd(), it first executes the reset() callback,
then enables the ohci interrupt, and finally executes the start()
callback. So moving the ohci_init() call which actually initializes the
reg field from start() to reset() should remove the race.

Tested by enabling the external HSIC hub in the bootloader on an exynos5
machine and booting. With the former code, this triggers an early interrupt
about 50% of the boots and a subsequent kernel panic in ohci_irq when trying
to access the registers.

Cc: Olof Johansson <olofj@chromium.org>
Cc: Doug Anderson <dianders@chromium.org>
Cc: Arjun.K.V <arjun.kv@samsung.com>
Cc: Vikas Sajjan <vikas.sajjan@samsung.com>
Cc: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ohci-exynos.c

@@ -23,6 +23,11 @@ struct exynos_ohci_hcd {
 	struct clk *clk;
 };
 
+static int ohci_exynos_reset(struct usb_hcd *hcd)
+{
+	return ohci_init(hcd_to_ohci(hcd));
+}
+
 static int ohci_exynos_start(struct usb_hcd *hcd)
 {
 	struct ohci_hcd *ohci = hcd_to_ohci(hcd);
@@ -30,10 +35,6 @@ static int ohci_exynos_start(struct usb_hcd *hcd)
 
 	ohci_dbg(ohci, "ohci_exynos_start, ohci:%p", ohci);
 
-	ret = ohci_init(ohci);
-	if (ret < 0)
-		return ret;
-
 	ret = ohci_run(ohci);
 	if (ret < 0) {
 		dev_err(hcd->self.controller, "can't start %s\n",
@@ -53,6 +54,7 @@ static const struct hc_driver exynos_ohci_hc_driver = {
 	.irq			= ohci_irq,
 	.flags			= HCD_MEMORY|HCD_USB11,
 
+	.reset			= ohci_exynos_reset,
 	.start			= ohci_exynos_start,
 	.stop			= ohci_stop,
 	.shutdown		= ohci_shutdown,