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

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Message-Id: <20160919063545.2055-1-joel@jms.id.au>
Date:   Mon, 19 Sep 2016 16:05:45 +0930
From:   Joel Stanley <joel@....id.au>
To:     linux-usb@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: [RFC PATCH] xhci: do not halt the secondary HCD

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@....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