From a5964396190d0c40dd549c23848c282fffa5d1f2 Mon Sep 17 00:00:00 2001 From: Rajmohan Mani Date: Wed, 18 Nov 2015 10:48:20 +0200 Subject: [PATCH] xhci: Workaround to get Intel xHCI reset working more reliably 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 Tested-by: Joe Lawrence Cc: stable Signed-off-by: Mathias Nyman Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/xhci.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c index 6e7dc6f93978..dfa44d3e8eee 100644 --- a/drivers/usb/host/xhci.c +++ b/drivers/usb/host/xhci.c @@ -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) -- 2.20.1