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 <j...@jms.id.au>
---
 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

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