[RFC PATCH] xhci: do not halt the secondary HCD

[Joel Stanley]

We can't halt the secondary HCD, because it's also the primary HCD,
which will cause problems if we have devices attached to the primary
HCD, like a keyboard.

We've been carrying this in our Linux-as-a-bootloader environment for a little
while now. The machines all have the same TI TUSB73x0 part, and when we kexec
the devices don't come back until a system power cycle.

I'd like some advice on an acceptable way to upstream the fix, so that the xhci
device survives kexec.

Signed-off-by: Joel Stanley <joel@xxxxxxxxx>
---
 drivers/usb/host/xhci.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index adc169d2fd76..ec92a843325b 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -682,6 +682,21 @@ void xhci_stop(struct usb_hcd *hcd)
 
 	mutex_lock(&xhci->mutex);
 
+	/*
+	 * We can't halt the secondary HCD, because it's also the primary
+	 * HCD, which will cause problems if we have devices attached to the
+	 * primary HCD, like a keyboard.
+	 */
+	if (!usb_hcd_is_primary_hcd(hcd)) {
+		/* The shared_hcd is going to be deallocated shortly (the USB
+		 * core only calls this function when allocation fails in
+		 * usb_add_hcd(), or usb_remove_hcd() is called).  So we need
+		 * to unset xHCI's pointer.  */
+		xhci->shared_hcd = NULL;
+		mutex_unlock(&xhci->mutex);
+		return;
+	}
+
 	if (!(xhci->xhc_state & XHCI_STATE_HALTED)) {
 		spin_lock_irq(&xhci->lock);
 
@@ -693,11 +708,6 @@ void xhci_stop(struct usb_hcd *hcd)
 		spin_unlock_irq(&xhci->lock);
 	}
 
-	if (!usb_hcd_is_primary_hcd(hcd)) {
-		mutex_unlock(&xhci->mutex);
-		return;
-	}
-
 	xhci_cleanup_msix(xhci);
 
 	/* Deleting Compliance Mode Recovery Timer */
-- 
2.9.3