Patch "xhci: Workaround to get Intel xHCI reset working more reliably" has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

xhci: Workaround to get Intel xHCI reset working more reliably

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xhci-workaround-to-get-intel-xhci-reset-working-more-reliably.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Rajmohan Mani <[email protected]>
Date: Wed, 18 Nov 2015 10:48:20 +0200
Subject: xhci: Workaround to get Intel xHCI reset working more reliably

From: Rajmohan Mani <[email protected]>

commit a5964396190d0c40dd549c23848c282fffa5d1f2 upstream.

Existing Intel xHCI controllers require a delay of 1 mS, after setting the CMD_RESET bit in command register, before accessing any HC registers. This allows the HC to complete the reset operation and be ready for HC register access. Without this delay, the subsequent HC register access, may result in a system hang, very rarely.

Verified CherryView / Braswell platforms go through over 5000 warm reboot cycles (which was not possible without this patch), without any xHCI reset hang.

---
 drivers/usb/host/xhci.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

@@ -175,6 +175,16 @@ int xhci_reset(struct xhci_hcd *xhci)
 	command |= CMD_RESET;
 	writel(command, &xhci->op_regs->command);
 
+	/* Existing Intel xHCI controllers require a delay of 1 mS,
+	 * after setting the CMD_RESET bit, and before accessing any
+	 * HC registers. This allows the HC to complete the
+	 * reset operation and be ready for HC register access.
+	 * Without this delay, the subsequent HC register access,
+	 * may result in a system hang very rarely.
+	 */
+	if (xhci->quirks & XHCI_INTEL_HOST)
+		udelay(1000);
+
 	ret = xhci_handshake(&xhci->op_regs->command,
 			CMD_RESET, 0, 10 * 1000 * 1000);
 	if (ret)

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/xhci-workaround-to-get-intel-xhci-reset-working-more-reliably.patch