@@ -176,6 +176,16 @@ 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, &xhci->op_regs->command,
CMD_RESET, 0, 10 * 1000 * 1000);
if (ret)
This is a note to let you know that I have just added a patch titled xhci: Workaround to get Intel xHCI reset working more reliably to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt22. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From ffeccda44b7b720fcdcf0437d90eae97c5fcf959 Mon Sep 17 00:00:00 2001 From: Rajmohan Mani <rajmohan.mani@intel.com> Date: Wed, 18 Nov 2015 10:48:20 +0200 Subject: xhci: Workaround to get Intel xHCI reset working more reliably 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. Signed-off-by: Rajmohan Mani <rajmohan.mani@intel.com> Tested-by: Joe Lawrence <joe.lawrence@stratus.com> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> [ luis: backported to 3.16: adjusted context ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/usb/host/xhci.c | 10 ++++++++++ 1 file changed, 10 insertions(+)