[PATCH] USB: EHCI and APM suspend

I've been having some problems with the EHCI driver on my Thinkpad T40,
running 2.6.9 with APM instead of ACPI.  On resume after suspend-to-RAM
the EHCI hardware keeps the interrupt line high, but the EHCI driver is
not clearing the interrupt status register, causing Linux to eventually
disable the interrupt altogether.

The attached patch for ehci-hub.c does the obvious thing: delay enabling
interrupts until hcd->state is set to USB_STATE_RUNNING.

From: Nickolai Zeldovich <nickolai@cs.stanford.edu>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/usb/host/ehci-hub.c

@@ -92,6 +92,7 @@ static int ehci_hub_resume (struct usb_hcd *hcd)
 	struct usb_device	*root = hcd_to_bus (&ehci->hcd)->root_hub;
 	u32			temp;
 	int			i;
+	int			intr_enable;
 
 	if (!root->dev.power.power_state)
 		return 0;
@@ -100,16 +101,17 @@ static int ehci_hub_resume (struct usb_hcd *hcd)
 
 	/* re-init operational registers in case we lost power */
 	if (readl (&ehci->regs->intr_enable) == 0) {
-		temp = 1;
-		writel (INTR_MASK, &ehci->regs->intr_enable);
+ 		/* at least some APM implementations will try to deliver
+		 * IRQs right away, so delay them until we're ready.
+ 		 */
+ 		intr_enable = 1;
 		writel (0, &ehci->regs->segment);
 		writel (ehci->periodic_dma, &ehci->regs->frame_list);
 		writel ((u32)ehci->async->qh_dma, &ehci->regs->async_next);
-		/* FIXME will this work even if (pci) vAUX was lost? */
 	} else
-		temp = 0;
+		intr_enable = 0;
 	ehci_dbg(ehci, "resume root hub%s\n",
-			temp ? " after power loss" : "");
+			intr_enable ? " after power loss" : "");
 
 	/* restore CMD_RUN, framelist size, and irq threshold */
 	writel (ehci->command, &ehci->regs->command);
@@ -151,6 +153,11 @@ static int ehci_hub_resume (struct usb_hcd *hcd)
 	root->dev.power.power_state = 0;
 	ehci->next_statechange = jiffies + msecs_to_jiffies(5);
 	ehci->hcd.state = USB_STATE_RUNNING;
+
+	/* Now we can safely re-enable irqs */
+	if (intr_enable)
+		writel (INTR_MASK, &ehci->regs->intr_enable);
+
 	return 0;
 }