Merge branch 'x86-debug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 debug updates from Ingo Molnar:
 "The biggest update is the addition of USB3 debug port based
  early-console.

  Greg was fine with the USB changes and with the routing of these
  patches:

    https://www.spinics.net/lists/linux-usb/msg155093.html"

* 'x86-debug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  usb/doc: Add document for USB3 debug port usage
  usb/serial: Add DBC debug device support to usb_debug
  x86/earlyprintk: Add support for earlyprintk via USB3 debug port
  usb/early: Add driver for xhci debug capability
  x86/timers: Add simple udelay calibration

11 files changed, 1438 insertions, 6 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ba294509cd7e..8d676d2a48ac 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -988,6 +988,7 @@
 			earlyprintk=ttySn[,baudrate]
 			earlyprintk=dbgp[debugController#]
 			earlyprintk=pciserial,bus:device.function[,baudrate]
+			earlyprintk=xdbc[xhciController#]
 
 			earlyprintk is useful when the kernel crashes before
 			the normal console is initialized. It is not enabled by
diff --git a/Documentation/usb/usb3-debug-port.rst b/Documentation/usb/usb3-debug-port.rst
new file mode 100644
index 000000000000..feb1a36a65b7
--- /dev/null
+++ b/Documentation/usb/usb3-debug-port.rst
@@ -0,0 +1,100 @@
+===============
+USB3 debug port
+===============
+
+:Author: Lu Baolu <baolu.lu@linux.intel.com>
+:Date: March 2017
+
+GENERAL
+=======
+
+This is a HOWTO for using the USB3 debug port on x86 systems.
+
+Before using any kernel debugging functionality based on USB3
+debug port, you need to::
+
+	1) check whether any USB3 debug port is available in
+	   your system;
+	2) check which port is used for debugging purposes;
+	3) have a USB 3.0 super-speed A-to-A debugging cable.
+
+INTRODUCTION
+============
+
+The xHCI debug capability (DbC) is an optional but standalone
+functionality provided by the xHCI host controller. The xHCI
+specification describes DbC in the section 7.6.
+
+When DbC is initialized and enabled, it will present a debug
+device through the debug port (normally the first USB3
+super-speed port). The debug device is fully compliant with
+the USB framework and provides the equivalent of a very high
+performance full-duplex serial link between the debug target
+(the system under debugging) and a debug host.
+
+EARLY PRINTK
+============
+
+DbC has been designed to log early printk messages. One use for
+this feature is kernel debugging. For example, when your machine
+crashes very early before the regular console code is initialized.
+Other uses include simpler, lockless logging instead of a full-
+blown printk console driver and klogd.
+
+On the debug target system, you need to customize a debugging
+kernel with CONFIG_EARLY_PRINTK_USB_XDBC enabled. And, add below
+kernel boot parameter::
+
+	"earlyprintk=xdbc"
+
+If there are multiple xHCI controllers in your system, you can
+append a host contoller index to this kernel parameter. This
+index starts from 0.
+
+Current design doesn't support DbC runtime suspend/resume. As
+the result, you'd better disable runtime power management for
+USB subsystem by adding below kernel boot parameter::
+
+	"usbcore.autosuspend=-1"
+
+Before starting the debug target, you should connect the debug
+port to a USB port (root port or port of any external hub) on
+the debug host. The cable used to connect these two ports
+should be a USB 3.0 super-speed A-to-A debugging cable.
+
+During early boot of the debug target, DbC will be detected and
+initialized. After initialization, the debug host should be able
+to enumerate the debug device in debug target. The debug host
+will then bind the debug device with the usb_debug driver module
+and create the /dev/ttyUSB device.
+
+If the debug device enumeration goes smoothly, you should be able
+to see below kernel messages on the debug host::
+
+	# tail -f /var/log/kern.log
+	[ 1815.983374] usb 4-3: new SuperSpeed USB device number 4 using xhci_hcd
+	[ 1815.999595] usb 4-3: LPM exit latency is zeroed, disabling LPM.
+	[ 1815.999899] usb 4-3: New USB device found, idVendor=1d6b, idProduct=0004
+	[ 1815.999902] usb 4-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
+	[ 1815.999903] usb 4-3: Product: Remote GDB
+	[ 1815.999904] usb 4-3: Manufacturer: Linux
+	[ 1815.999905] usb 4-3: SerialNumber: 0001
+	[ 1816.000240] usb_debug 4-3:1.0: xhci_dbc converter detected
+	[ 1816.000360] usb 4-3: xhci_dbc converter now attached to ttyUSB0
+
+You can use any communication program, for example minicom, to
+read and view the messages. Below simple bash scripts can help
+you to check the sanity of the setup.
+
+.. code-block:: sh
+
+	===== start of bash scripts =============
+	#!/bin/bash
+
+	while true ; do
+		while [ ! -d /sys/class/tty/ttyUSB0 ] ; do
+			:
+		done
+	cat /dev/ttyUSB0
+	done
+	===== end of bash scripts ===============
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 63c1d13aaf9f..fcb7604172ce 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -5,6 +5,9 @@ config TRACE_IRQFLAGS_SUPPORT
 
 source "lib/Kconfig.debug"
 
+config EARLY_PRINTK_USB
+	bool
+
 config X86_VERBOSE_BOOTUP
 	bool "Enable verbose x86 bootup info messages"
 	default y
@@ -23,19 +26,20 @@ config EARLY_PRINTK
 	  This is useful for kernel debugging when your machine crashes very
 	  early before the console code is initialized. For normal operation
 	  it is not recommended because it looks ugly and doesn't cooperate
-	  with klogd/syslogd or the X server. You should normally N here,
+	  with klogd/syslogd or the X server. You should normally say N here,
 	  unless you want to debug such a crash.
 
 config EARLY_PRINTK_DBGP
 	bool "Early printk via EHCI debug port"
 	depends on EARLY_PRINTK && PCI
+	select EARLY_PRINTK_USB
 	---help---
 	  Write kernel log output directly into the EHCI debug port.
 
 	  This is useful for kernel debugging when your machine crashes very
 	  early before the console code is initialized. For normal operation
 	  it is not recommended because it looks ugly and doesn't cooperate
-	  with klogd/syslogd or the X server. You should normally N here,
+	  with klogd/syslogd or the X server. You should normally say N here,
 	  unless you want to debug such a crash. You need usb debug device.
 
 config EARLY_PRINTK_EFI
@@ -48,6 +52,25 @@ config EARLY_PRINTK_EFI
 	  This is useful for kernel debugging when your machine crashes very
 	  early before the console code is initialized.
 
+config EARLY_PRINTK_USB_XDBC
+	bool "Early printk via the xHCI debug port"
+	depends on EARLY_PRINTK && PCI
+	select EARLY_PRINTK_USB
+	---help---
+	  Write kernel log output directly into the xHCI debug port.
+
+	  One use for this feature is kernel debugging, for example when your
+	  machine crashes very early before the regular console code is
+	  initialized. Other uses include simpler, lockless logging instead of
+	  a full-blown printk console driver + klogd.
+
+	  For normal production environments this is normally not recommended,
+	  because it doesn't feed events into klogd/syslogd and doesn't try to
+	  print anything on the screen.
+
+	  You should normally say N here, unless you want to debug early
+	  crashes or need a very simple printk logging facility.
+
 config X86_PTDUMP_CORE
 	def_bool n
 
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 8a121991e5ba..0f0840304452 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -17,6 +17,7 @@
 #include <asm/intel-mid.h>
 #include <asm/pgtable.h>
 #include <linux/usb/ehci_def.h>
+#include <linux/usb/xhci-dbgp.h>
 #include <linux/efi.h>
 #include <asm/efi.h>
 #include <asm/pci_x86.h>
@@ -381,6 +382,10 @@ static int __init setup_early_printk(char *buf)
 		if (!strncmp(buf, "efi", 3))
 			early_console_register(&early_efi_console, keep);
 #endif
+#ifdef CONFIG_EARLY_PRINTK_USB_XDBC
+		if (!strncmp(buf, "xdbc", 4))
+			early_xdbc_parse_parameter(buf + 4);
+#endif
 
 		buf++;
 	}
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 62a1c74855e5..0b4d3c686b1e 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -70,6 +70,7 @@
 #include <linux/tboot.h>
 #include <linux/jiffies.h>
 
+#include <linux/usb/xhci-dbgp.h>
 #include <video/edid.h>
 
 #include <asm/mtrr.h>
@@ -811,6 +812,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
 	return 0;
 }
 
+static void __init simple_udelay_calibration(void)
+{
+	unsigned int tsc_khz, cpu_khz;
+	unsigned long lpj;
+
+	if (!boot_cpu_has(X86_FEATURE_TSC))
+		return;
+
+	cpu_khz = x86_platform.calibrate_cpu();
+	tsc_khz = x86_platform.calibrate_tsc();
+
+	tsc_khz = tsc_khz ? : cpu_khz;
+	if (!tsc_khz)
+		return;
+
+	lpj = tsc_khz * 1000;
+	do_div(lpj, HZ);
+	loops_per_jiffy = lpj;
+}
+
 /*
  * Determine if we were loaded by an EFI loader.  If so, then we have also been
  * passed the efi memmap, systab, etc., so we should use these data structures
@@ -959,6 +980,8 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	x86_configure_nx();
 
+	simple_udelay_calibration();
+
 	parse_early_param();
 
 #ifdef CONFIG_MEMORY_HOTPLUG
@@ -1095,6 +1118,9 @@ void __init setup_arch(char **cmdline_p)
 	memblock_set_current_limit(ISA_END_ADDRESS);
 	e820__memblock_setup();
 
+	if (!early_xdbc_setup_hardware())
+		early_xdbc_register_console();
+
 	reserve_bios_regions();
 
 	if (efi_enabled(EFI_MEMMAP)) {
diff --git a/drivers/usb/Makefile b/drivers/usb/Makefile
index 7791af6c102c..53d1356bbd06 100644
--- a/drivers/usb/Makefile
+++ b/drivers/usb/Makefile
@@ -49,7 +49,7 @@ obj-$(CONFIG_USB_MICROTEK)	+= image/
 obj-$(CONFIG_USB_SERIAL)	+= serial/
 
 obj-$(CONFIG_USB)		+= misc/
-obj-$(CONFIG_EARLY_PRINTK_DBGP)	+= early/
+obj-$(CONFIG_EARLY_PRINTK_USB)	+= early/
 
 obj-$(CONFIG_USB_ATM)		+= atm/
 obj-$(CONFIG_USB_SPEEDTOUCH)	+= atm/
diff --git a/drivers/usb/early/Makefile b/drivers/usb/early/Makefile
index 24bbe519c737..fcde2286da1c 100644
--- a/drivers/usb/early/Makefile
+++ b/drivers/usb/early/Makefile
@@ -3,3 +3,4 @@
 #
 
 obj-$(CONFIG_EARLY_PRINTK_DBGP) += ehci-dbgp.o
+obj-$(CONFIG_EARLY_PRINTK_USB_XDBC) += xhci-dbc.o
diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
new file mode 100644
index 000000000000..1268818e2263
--- /dev/null
+++ b/drivers/usb/early/xhci-dbc.c
@@ -0,0 +1,1014 @@
+/**
+ * xhci-dbc.c - xHCI debug capability early driver
+ *
+ * Copyright (C) 2016 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#define pr_fmt(fmt)	KBUILD_MODNAME ":%s: " fmt, __func__
+
+#include <linux/console.h>
+#include <linux/pci_regs.h>
+#include <linux/pci_ids.h>
+#include <linux/bootmem.h>
+#include <linux/io.h>
+#include <asm/pci-direct.h>
+#include <asm/fixmap.h>
+#include <linux/bcd.h>
+#include <linux/export.h>
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+
+#include "../host/xhci.h"
+#include "xhci-dbc.h"
+
+static struct xdbc_state xdbc;
+static bool early_console_keep;
+
+#define XDBC_TRACE
+#ifdef XDBC_TRACE
+#define	xdbc_trace	trace_printk
+#else
+static inline void xdbc_trace(const char *fmt, ...) { }
+#endif /* XDBC_TRACE */
+
+static void __iomem * __init xdbc_map_pci_mmio(u32 bus, u32 dev, u32 func)
+{
+	u64 val64, sz64, mask64;
+	void __iomem *base;
+	u32 val, sz;
+	u8 byte;
+
+	val = read_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0);
+	write_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0, ~0);
+	sz = read_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0);
+	write_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0, val);
+
+	if (val == 0xffffffff || sz == 0xffffffff) {
+		pr_notice("invalid mmio bar\n");
+		return NULL;
+	}
+
+	val64	= val & PCI_BASE_ADDRESS_MEM_MASK;
+	sz64	= sz & PCI_BASE_ADDRESS_MEM_MASK;
+	mask64	= PCI_BASE_ADDRESS_MEM_MASK;
+
+	if ((val & PCI_BASE_ADDRESS_MEM_TYPE_MASK) == PCI_BASE_ADDRESS_MEM_TYPE_64) {
+		val = read_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0 + 4);
+		write_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0 + 4, ~0);
+		sz = read_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0 + 4);
+		write_pci_config(bus, dev, func, PCI_BASE_ADDRESS_0 + 4, val);
+
+		val64	|= (u64)val << 32;
+		sz64	|= (u64)sz << 32;
+		mask64	|= ~0ULL << 32;
+	}
+
+	sz64 &= mask64;
+
+	if (!sz64) {
+		pr_notice("invalid mmio address\n");
+		return NULL;
+	}
+
+	sz64 = 1ULL << __ffs64(sz64);
+
+	/* Check if the mem space is enabled: */
+	byte = read_pci_config_byte(bus, dev, func, PCI_COMMAND);
+	if (!(byte & PCI_COMMAND_MEMORY)) {
+		byte |= PCI_COMMAND_MEMORY;
+		write_pci_config_byte(bus, dev, func, PCI_COMMAND, byte);
+	}
+
+	xdbc.xhci_start = val64;
+	xdbc.xhci_length = sz64;
+	base = early_ioremap(val64, sz64);
+
+	return base;
+}
+
+static void * __init xdbc_get_page(dma_addr_t *dma_addr)
+{
+	void *virt;
+
+	virt = alloc_bootmem_pages_nopanic(PAGE_SIZE);
+	if (!virt)
+		return NULL;
+
+	if (dma_addr)
+		*dma_addr = (dma_addr_t)__pa(virt);
+
+	return virt;
+}
+
+static u32 __init xdbc_find_dbgp(int xdbc_num, u32 *b, u32 *d, u32 *f)
+{
+	u32 bus, dev, func, class;
+
+	for (bus = 0; bus < XDBC_PCI_MAX_BUSES; bus++) {
+		for (dev = 0; dev < XDBC_PCI_MAX_DEVICES; dev++) {
+			for (func = 0; func < XDBC_PCI_MAX_FUNCTION; func++) {
+
+				class = read_pci_config(bus, dev, func, PCI_CLASS_REVISION);
+				if ((class >> 8) != PCI_CLASS_SERIAL_USB_XHCI)
+					continue;
+
+				if (xdbc_num-- != 0)
+					continue;
+
+				*b = bus;
+				*d = dev;
+				*f = func;
+
+				return 0;
+			}
+		}
+	}
+
+	return -1;
+}
+
+static int handshake(void __iomem *ptr, u32 mask, u32 done, int wait, int delay)
+{
+	u32 result;
+
+	do {
+		result = readl(ptr);
+		result &= mask;
+		if (result == done)
+			return 0;
+		udelay(delay);
+		wait -= delay;
+	} while (wait > 0);
+
+	return -ETIMEDOUT;
+}
+
+static void __init xdbc_bios_handoff(void)
+{
+	int offset, timeout;
+	u32 val;
+
+	offset = xhci_find_next_ext_cap(xdbc.xhci_base, 0, XHCI_EXT_CAPS_LEGACY);
+	val = readl(xdbc.xhci_base + offset);
+
+	if (val & XHCI_HC_BIOS_OWNED) {
+		writel(val | XHCI_HC_OS_OWNED, xdbc.xhci_base + offset);
+		timeout = handshake(xdbc.xhci_base + offset, XHCI_HC_BIOS_OWNED, 0, 5000, 10);
+
+		if (timeout) {
+			pr_notice("failed to hand over xHCI control from BIOS\n");
+			writel(val & ~XHCI_HC_BIOS_OWNED, xdbc.xhci_base + offset);
+		}
+	}
+
+	/* Disable BIOS SMIs and clear all SMI events: */
+	val = readl(xdbc.xhci_base + offset + XHCI_LEGACY_CONTROL_OFFSET);
+	val &= XHCI_LEGACY_DISABLE_SMI;
+	val |= XHCI_LEGACY_SMI_EVENTS;
+	writel(val, xdbc.xhci_base + offset + XHCI_LEGACY_CONTROL_OFFSET);
+}
+
+static int __init
+xdbc_alloc_ring(struct xdbc_segment *seg, struct xdbc_ring *ring)
+{
+	seg->trbs = xdbc_get_page(&seg->dma);
+	if (!seg->trbs)
+		return -ENOMEM;
+
+	ring->segment = seg;
+
+	return 0;
+}
+
+static void __init xdbc_free_ring(struct xdbc_ring *ring)
+{
+	struct xdbc_segment *seg = ring->segment;
+
+	if (!seg)
+		return;
+
+	free_bootmem(seg->dma, PAGE_SIZE);
+	ring->segment = NULL;
+}
+
+static void xdbc_reset_ring(struct xdbc_ring *ring)
+{
+	struct xdbc_segment *seg = ring->segment;
+	struct xdbc_trb *link_trb;
+
+	memset(seg->trbs, 0, PAGE_SIZE);
+
+	ring->enqueue = seg->trbs;
+	ring->dequeue = seg->trbs;
+	ring->cycle_state = 1;
+
+	if (ring != &xdbc.evt_ring) {
+		link_trb = &seg->trbs[XDBC_TRBS_PER_SEGMENT - 1];
+		link_trb->field[0] = cpu_to_le32(lower_32_bits(seg->dma));
+		link_trb->field[1] = cpu_to_le32(upper_32_bits(seg->dma));
+		link_trb->field[3] = cpu_to_le32(TRB_TYPE(TRB_LINK)) | cpu_to_le32(LINK_TOGGLE);
+	}
+}
+
+static inline void xdbc_put_utf16(u16 *s, const char *c, size_t size)
+{
+	int i;
+
+	for (i = 0; i < size; i++)
+		s[i] = cpu_to_le16(c[i]);
+}
+
+static void xdbc_mem_init(void)
+{
+	struct xdbc_ep_context *ep_in, *ep_out;
+	struct usb_string_descriptor *s_desc;
+	struct xdbc_erst_entry *entry;
+	struct xdbc_strings *strings;
+	struct xdbc_context *ctx;
+	unsigned int max_burst;
+	u32 string_length;
+	int index = 0;
+	u32 dev_info;
+
+	xdbc_reset_ring(&xdbc.evt_ring);
+	xdbc_reset_ring(&xdbc.in_ring);
+	xdbc_reset_ring(&xdbc.out_ring);
+	memset(xdbc.table_base, 0, PAGE_SIZE);
+	memset(xdbc.out_buf, 0, PAGE_SIZE);
+
+	/* Initialize event ring segment table: */
+	xdbc.erst_size	= 16;
+	xdbc.erst_base	= xdbc.table_base + index * XDBC_TABLE_ENTRY_SIZE;
+	xdbc.erst_dma	= xdbc.table_dma + index * XDBC_TABLE_ENTRY_SIZE;
+
+	index += XDBC_ERST_ENTRY_NUM;
+	entry = (struct xdbc_erst_entry *)xdbc.erst_base;
+
+	entry->seg_addr		= cpu_to_le64(xdbc.evt_seg.dma);
+	entry->seg_size		= cpu_to_le32(XDBC_TRBS_PER_SEGMENT);
+	entry->__reserved_0	= 0;
+
+	/* Initialize ERST registers: */
+	writel(1, &xdbc.xdbc_reg->ersts);
+	xdbc_write64(xdbc.erst_dma, &xdbc.xdbc_reg->erstba);
+	xdbc_write64(xdbc.evt_seg.dma, &xdbc.xdbc_reg->erdp);
+
+	/* Debug capability contexts: */
+	xdbc.dbcc_size	= 64 * 3;
+	xdbc.dbcc_base	= xdbc.table_base + index * XDBC_TABLE_ENTRY_SIZE;
+	xdbc.dbcc_dma	= xdbc.table_dma + index * XDBC_TABLE_ENTRY_SIZE;
+
+	index += XDBC_DBCC_ENTRY_NUM;
+
+	/* Popluate the strings: */
+	xdbc.string_size = sizeof(struct xdbc_strings);
+	xdbc.string_base = xdbc.table_base + index * XDBC_TABLE_ENTRY_SIZE;
+	xdbc.string_dma	 = xdbc.table_dma + index * XDBC_TABLE_ENTRY_SIZE;
+	strings		 = (struct xdbc_strings *)xdbc.string_base;
+
+	index += XDBC_STRING_ENTRY_NUM;
+
+	/* Serial string: */
+	s_desc			= (struct usb_string_descriptor *)strings->serial;
+	s_desc->bLength		= (strlen(XDBC_STRING_SERIAL) + 1) * 2;
+	s_desc->bDescriptorType	= USB_DT_STRING;
+
+	xdbc_put_utf16(s_desc->wData, XDBC_STRING_SERIAL, strlen(XDBC_STRING_SERIAL));
+	string_length = s_desc->bLength;
+	string_length <<= 8;
+
+	/* Product string: */
+	s_desc			= (struct usb_string_descriptor *)strings->product;
+	s_desc->bLength		= (strlen(XDBC_STRING_PRODUCT) + 1) * 2;
+	s_desc->bDescriptorType	= USB_DT_STRING;
+
+	xdbc_put_utf16(s_desc->wData, XDBC_STRING_PRODUCT, strlen(XDBC_STRING_PRODUCT));
+	string_length += s_desc->bLength;
+	string_length <<= 8;
+
+	/* Manufacture string: */
+	s_desc			= (struct usb_string_descriptor *)strings->manufacturer;
+	s_desc->bLength		= (strlen(XDBC_STRING_MANUFACTURER) + 1) * 2;
+	s_desc->bDescriptorType	= USB_DT_STRING;
+
+	xdbc_put_utf16(s_desc->wData, XDBC_STRING_MANUFACTURER, strlen(XDBC_STRING_MANUFACTURER));
+	string_length += s_desc->bLength;
+	string_length <<= 8;
+
+	/* String0: */
+	strings->string0[0]	= 4;
+	strings->string0[1]	= USB_DT_STRING;
+	strings->string0[2]	= 0x09;
+	strings->string0[3]	= 0x04;
+
+	string_length += 4;
+
+	/* Populate info Context: */
+	ctx = (struct xdbc_context *)xdbc.dbcc_base;
+
+	ctx->info.string0	= cpu_to_le64(xdbc.string_dma);
+	ctx->info.manufacturer	= cpu_to_le64(xdbc.string_dma + XDBC_MAX_STRING_LENGTH);
+	ctx->info.product	= cpu_to_le64(xdbc.string_dma + XDBC_MAX_STRING_LENGTH * 2);
+	ctx->info.serial	= cpu_to_le64(xdbc.string_dma + XDBC_MAX_STRING_LENGTH * 3);
+	ctx->info.length	= cpu_to_le32(string_length);
+
+	/* Populate bulk out endpoint context: */
+	max_burst = DEBUG_MAX_BURST(readl(&xdbc.xdbc_reg->control));
+	ep_out = (struct xdbc_ep_context *)&ctx->out;
+
+	ep_out->ep_info1	= 0;
+	ep_out->ep_info2	= cpu_to_le32(EP_TYPE(BULK_OUT_EP) | MAX_PACKET(1024) | MAX_BURST(max_burst));
+	ep_out->deq		= cpu_to_le64(xdbc.out_seg.dma | xdbc.out_ring.cycle_state);
+
+	/* Populate bulk in endpoint context: */
+	ep_in = (struct xdbc_ep_context *)&ctx->in;
+
+	ep_in->ep_info1		= 0;
+	ep_in->ep_info2		= cpu_to_le32(EP_TYPE(BULK_OUT_EP) | MAX_PACKET(1024) | MAX_BURST(max_burst));
+	ep_in->deq		= cpu_to_le64(xdbc.in_seg.dma | xdbc.in_ring.cycle_state);
+
+	/* Set DbC context and info registers: */
+	xdbc_write64(xdbc.dbcc_dma, &xdbc.xdbc_reg->dccp);
+
+	dev_info = cpu_to_le32((XDBC_VENDOR_ID << 16) | XDBC_PROTOCOL);
+	writel(dev_info, &xdbc.xdbc_reg->devinfo1);
+
+	dev_info = cpu_to_le32((XDBC_DEVICE_REV << 16) | XDBC_PRODUCT_ID);
+	writel(dev_info, &xdbc.xdbc_reg->devinfo2);
+
+	xdbc.in_buf = xdbc.out_buf + XDBC_MAX_PACKET;
+	xdbc.in_dma = xdbc.out_dma + XDBC_MAX_PACKET;
+}
+
+static void xdbc_do_reset_debug_port(u32 id, u32 count)
+{
+	void __iomem *ops_reg;
+	void __iomem *portsc;
+	u32 val, cap_length;
+	int i;
+
+	cap_length = readl(xdbc.xhci_base) & 0xff;
+	ops_reg = xdbc.xhci_base + cap_length;
+
+	id--;
+	for (i = id; i < (id + count); i++) {
+		portsc = ops_reg + 0x400 + i * 0x10;
+		val = readl(portsc);
+		if (!(val & PORT_CONNECT))
+			writel(val | PORT_RESET, portsc);
+	}
+}
+
+static void xdbc_reset_debug_port(void)
+{
+	u32 val, port_offset, port_count;
+	int offset = 0;
+
+	do {
+		offset = xhci_find_next_ext_cap(xdbc.xhci_base, offset, XHCI_EXT_CAPS_PROTOCOL);
+		if (!offset)
+			break;
+
+		val = readl(xdbc.xhci_base + offset);
+		if (XHCI_EXT_PORT_MAJOR(val) != 0x3)
+			continue;
+
+		val = readl(xdbc.xhci_base + offset + 8);
+		port_offset = XHCI_EXT_PORT_OFF(val);
+		port_count = XHCI_EXT_PORT_COUNT(val);
+
+		xdbc_do_reset_debug_port(port_offset, port_count);
+	} while (1);
+}
+
+static void
+xdbc_queue_trb(struct xdbc_ring *ring, u32 field1, u32 field2, u32 field3, u32 field4)
+{
+	struct xdbc_trb *trb, *link_trb;
+
+	trb = ring->enqueue;
+	trb->field[0] = cpu_to_le32(field1);
+	trb->field[1] = cpu_to_le32(field2);
+	trb->field[2] = cpu_to_le32(field3);
+	trb->field[3] = cpu_to_le32(field4);
+
+	++(ring->enqueue);
+	if (ring->enqueue >= &ring->segment->trbs[TRBS_PER_SEGMENT - 1]) {
+		link_trb = ring->enqueue;
+		if (ring->cycle_state)
+			link_trb->field[3] |= cpu_to_le32(TRB_CYCLE);
+		else
+			link_trb->field[3] &= cpu_to_le32(~TRB_CYCLE);
+
+		ring->enqueue = ring->segment->trbs;
+		ring->cycle_state ^= 1;
+	}
+}
+
+static void xdbc_ring_doorbell(int target)
+{
+	writel(DOOR_BELL_TARGET(target), &xdbc.xdbc_reg->doorbell);
+}
+
+static int xdbc_start(void)
+{
+	u32 ctrl, status;
+	int ret;
+
+	ctrl = readl(&xdbc.xdbc_reg->control);
+	writel(ctrl | CTRL_DBC_ENABLE | CTRL_PORT_ENABLE, &xdbc.xdbc_reg->control);
+	ret = handshake(&xdbc.xdbc_reg->control, CTRL_DBC_ENABLE, CTRL_DBC_ENABLE, 100000, 100);
+	if (ret) {
+		xdbc_trace("failed to initialize hardware\n");
+		return ret;
+	}
+
+	/* Reset port to avoid bus hang: */
+	if (xdbc.vendor == PCI_VENDOR_ID_INTEL)
+		xdbc_reset_debug_port();
+
+	/* Wait for port connection: */
+	ret = handshake(&xdbc.xdbc_reg->portsc, PORTSC_CONN_STATUS, PORTSC_CONN_STATUS, 5000000, 100);
+	if (ret) {
+		xdbc_trace("waiting for connection timed out\n");
+		return ret;
+	}
+
+	/* Wait for debug device to be configured: */
+	ret = handshake(&xdbc.xdbc_reg->control, CTRL_DBC_RUN, CTRL_DBC_RUN, 5000000, 100);
+	if (ret) {
+		xdbc_trace("waiting for device configuration timed out\n");
+		return ret;
+	}
+
+	/* Check port number: */
+	status = readl(&xdbc.xdbc_reg->status);
+	if (!DCST_DEBUG_PORT(status)) {
+		xdbc_trace("invalid root hub port number\n");
+		return -ENODEV;
+	}
+
+	xdbc.port_number = DCST_DEBUG_PORT(status);
+
+	xdbc_trace("DbC is running now, control 0x%08x port ID %d\n",
+		   readl(&xdbc.xdbc_reg->control), xdbc.port_number);
+
+	return 0;
+}
+
+static int xdbc_bulk_transfer(void *data, int size, bool read)
+{
+	struct xdbc_ring *ring;
+	struct xdbc_trb *trb;
+	u32 length, control;
+	u32 cycle;
+	u64 addr;
+
+	if (size > XDBC_MAX_PACKET) {
+		xdbc_trace("bad parameter, size %d\n", size);
+		return -EINVAL;
+	}
+
+	if (!(xdbc.flags & XDBC_FLAGS_INITIALIZED) ||
+	    !(xdbc.flags & XDBC_FLAGS_CONFIGURED) ||
+	    (!read && (xdbc.flags & XDBC_FLAGS_OUT_STALL)) ||
+	    (read && (xdbc.flags & XDBC_FLAGS_IN_STALL))) {
+
+		xdbc_trace("connection not ready, flags %08x\n", xdbc.flags);
+		return -EIO;
+	}
+
+	ring = (read ? &xdbc.in_ring : &xdbc.out_ring);
+	trb = ring->enqueue;
+	cycle = ring->cycle_state;
+	length = TRB_LEN(size);
+	control = TRB_TYPE(TRB_NORMAL) | TRB_IOC;
+
+	if (cycle)
+		control &= cpu_to_le32(~TRB_CYCLE);
+	else
+		control |= cpu_to_le32(TRB_CYCLE);
+
+	if (read) {
+		memset(xdbc.in_buf, 0, XDBC_MAX_PACKET);
+		addr = xdbc.in_dma;
+		xdbc.flags |= XDBC_FLAGS_IN_PROCESS;
+	} else {
+		memset(xdbc.out_buf, 0, XDBC_MAX_PACKET);
+		memcpy(xdbc.out_buf, data, size);
+		addr = xdbc.out_dma;
+		xdbc.flags |= XDBC_FLAGS_OUT_PROCESS;
+	}
+
+	xdbc_queue_trb(ring, lower_32_bits(addr), upper_32_bits(addr), length, control);
+
+	/*
+	 * Add a barrier between writes of trb fields and flipping
+	 * the cycle bit:
+	 */
+	wmb();
+	if (cycle)
+		trb->field[3] |= cpu_to_le32(cycle);
+	else
+		trb->field[3] &= cpu_to_le32(~TRB_CYCLE);
+
+	xdbc_ring_doorbell(read ? IN_EP_DOORBELL : OUT_EP_DOORBELL);
+
+	return size;
+}
+
+static int xdbc_handle_external_reset(void)
+{
+	int ret = 0;
+
+	xdbc.flags = 0;
+	writel(0, &xdbc.xdbc_reg->control);
+	ret = handshake(&xdbc.xdbc_reg->control, CTRL_DBC_ENABLE, 0, 100000, 10);
+	if (ret)
+		goto reset_out;
+
+	xdbc_mem_init();
+
+	mmiowb();
+
+	ret = xdbc_start();
+	if (ret < 0)
+		goto reset_out;
+
+	xdbc_trace("dbc recovered\n");
+
+	xdbc.flags |= XDBC_FLAGS_INITIALIZED | XDBC_FLAGS_CONFIGURED;
+
+	xdbc_bulk_transfer(NULL, XDBC_MAX_PACKET, true);
+
+	return 0;
+
+reset_out:
+	xdbc_trace("failed to recover from external reset\n");
+	return ret;
+}
+
+static int __init xdbc_early_setup(void)
+{
+	int ret;
+
+	writel(0, &xdbc.xdbc_reg->control);
+	ret = handshake(&xdbc.xdbc_reg->control, CTRL_DBC_ENABLE, 0, 100000, 100);
+	if (ret)
+		return ret;
+
+	/* Allocate the table page: */
+	xdbc.table_base = xdbc_get_page(&xdbc.table_dma);
+	if (!xdbc.table_base)
+		return -ENOMEM;
+
+	/* Get and store the transfer buffer: */
+	xdbc.out_buf = xdbc_get_page(&xdbc.out_dma);
+	if (!xdbc.out_buf)
+		return -ENOMEM;
+
+	/* Allocate the event ring: */
+	ret = xdbc_alloc_ring(&xdbc.evt_seg, &xdbc.evt_ring);
+	if (ret < 0)
+		return ret;
+
+	/* Allocate IN/OUT endpoint transfer rings: */
+	ret = xdbc_alloc_ring(&xdbc.in_seg, &xdbc.in_ring);
+	if (ret < 0)
+		return ret;
+
+	ret = xdbc_alloc_ring(&xdbc.out_seg, &xdbc.out_ring);
+	if (ret < 0)
+		return ret;
+
+	xdbc_mem_init();
+
+	mmiowb();
+
+	ret = xdbc_start();
+	if (ret < 0) {
+		writel(0, &xdbc.xdbc_reg->control);
+		return ret;
+	}
+
+	xdbc.flags |= XDBC_FLAGS_INITIALIZED | XDBC_FLAGS_CONFIGURED;
+
+	xdbc_bulk_transfer(NULL, XDBC_MAX_PACKET, true);
+
+	return 0;
+}
+
+int __init early_xdbc_parse_parameter(char *s)
+{
+	unsigned long dbgp_num = 0;
+	u32 bus, dev, func, offset;
+	int ret;
+
+	if (!early_pci_allowed())
+		return -EPERM;
+
+	if (strstr(s, "keep"))
+		early_console_keep = true;
+
+	if (xdbc.xdbc_reg)
+		return 0;
+
+	if (*s && kstrtoul(s, 0, &dbgp_num))
+		dbgp_num = 0;
+
+	pr_notice("dbgp_num: %lu\n", dbgp_num);
+
+	/* Locate the host controller: */
+	ret = xdbc_find_dbgp(dbgp_num, &bus, &dev, &func);
+	if (ret) {
+		pr_notice("failed to locate xhci host\n");
+		return -ENODEV;
+	}
+
+	xdbc.vendor	= read_pci_config_16(bus, dev, func, PCI_VENDOR_ID);
+	xdbc.device	= read_pci_config_16(bus, dev, func, PCI_DEVICE_ID);
+	xdbc.bus	= bus;
+	xdbc.dev	= dev;
+	xdbc.func	= func;
+
+	/* Map the IO memory: */
+	xdbc.xhci_base = xdbc_map_pci_mmio(bus, dev, func);
+	if (!xdbc.xhci_base)
+		return -EINVAL;
+
+	/* Locate DbC registers: */
+	offset = xhci_find_next_ext_cap(xdbc.xhci_base, 0, XHCI_EXT_CAPS_DEBUG);
+	if (!offset) {
+		pr_notice("xhci host doesn't support debug capability\n");
+		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
+		xdbc.xhci_base = NULL;
+		xdbc.xhci_length = 0;
+
+		return -ENODEV;
+	}
+	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
+
+	return 0;
+}
+
+int __init early_xdbc_setup_hardware(void)
+{
+	int ret;
+
+	if (!xdbc.xdbc_reg)
+		return -ENODEV;
+
+	xdbc_bios_handoff();
+
+	raw_spin_lock_init(&xdbc.lock);
+
+	ret = xdbc_early_setup();
+	if (ret) {
+		pr_notice("failed to setup the connection to host\n");
+
+		xdbc_free_ring(&xdbc.evt_ring);
+		xdbc_free_ring(&xdbc.out_ring);
+		xdbc_free_ring(&xdbc.in_ring);
+
+		if (xdbc.table_dma)
+			free_bootmem(xdbc.table_dma, PAGE_SIZE);
+
+		if (xdbc.out_dma)
+			free_bootmem(xdbc.out_dma, PAGE_SIZE);
+
+		xdbc.table_base = NULL;
+		xdbc.out_buf = NULL;
+	}
+
+	return ret;
+}
+
+static void xdbc_handle_port_status(struct xdbc_trb *evt_trb)
+{
+	u32 port_reg;
+
+	port_reg = readl(&xdbc.xdbc_reg->portsc);
+	if (port_reg & PORTSC_CONN_CHANGE) {
+		xdbc_trace("connect status change event\n");
+
+		/* Check whether cable unplugged: */
+		if (!(port_reg & PORTSC_CONN_STATUS)) {
+			xdbc.flags = 0;
+			xdbc_trace("cable unplugged\n");
+		}
+	}
+
+	if (port_reg & PORTSC_RESET_CHANGE)
+		xdbc_trace("port reset change event\n");
+
+	if (port_reg & PORTSC_LINK_CHANGE)
+		xdbc_trace("port link status change event\n");
+
+	if (port_reg & PORTSC_CONFIG_CHANGE)
+		xdbc_trace("config error change\n");
+
+	/* Write back the value to clear RW1C bits: */
+	writel(port_reg, &xdbc.xdbc_reg->portsc);
+}
+
+static void xdbc_handle_tx_event(struct xdbc_trb *evt_trb)
+{
+	size_t remain_length;
+	u32 comp_code;
+	int ep_id;
+
+	comp_code	= GET_COMP_CODE(le32_to_cpu(evt_trb->field[2]));
+	remain_length	= EVENT_TRB_LEN(le32_to_cpu(evt_trb->field[2]));
+	ep_id		= TRB_TO_EP_ID(le32_to_cpu(evt_trb->field[3]));
+
+	switch (comp_code) {
+	case COMP_SUCCESS:
+		remain_length = 0;
+	case COMP_SHORT_PACKET:
+		break;
+	case COMP_TRB_ERROR:
+	case COMP_BABBLE_DETECTED_ERROR:
+	case COMP_USB_TRANSACTION_ERROR:
+	case COMP_STALL_ERROR:
+	default:
+		if (ep_id == XDBC_EPID_OUT)
+			xdbc.flags |= XDBC_FLAGS_OUT_STALL;
+		if (ep_id == XDBC_EPID_IN)
+			xdbc.flags |= XDBC_FLAGS_IN_STALL;
+
+		xdbc_trace("endpoint %d stalled\n", ep_id);
+		break;
+	}
+
+	if (ep_id == XDBC_EPID_IN) {
+		xdbc.flags &= ~XDBC_FLAGS_IN_PROCESS;
+		xdbc_bulk_transfer(NULL, XDBC_MAX_PACKET, true);
+	} else if (ep_id == XDBC_EPID_OUT) {
+		xdbc.flags &= ~XDBC_FLAGS_OUT_PROCESS;
+	} else {
+		xdbc_trace("invalid endpoint id %d\n", ep_id);
+	}
+}
+
+static void xdbc_handle_events(void)
+{
+	struct xdbc_trb *evt_trb;
+	bool update_erdp = false;
+	u32 reg;
+	u8 cmd;
+
+	cmd = read_pci_config_byte(xdbc.bus, xdbc.dev, xdbc.func, PCI_COMMAND);
+	if (!(cmd & PCI_COMMAND_MASTER)) {
+		cmd |= PCI_COMMAND_MASTER | PCI_COMMAND_MEMORY;
+		write_pci_config_byte(xdbc.bus, xdbc.dev, xdbc.func, PCI_COMMAND, cmd);
+	}
+
+	if (!(xdbc.flags & XDBC_FLAGS_INITIALIZED))
+		return;
+
+	/* Handle external reset events: */
+	reg = readl(&xdbc.xdbc_reg->control);
+	if (!(reg & CTRL_DBC_ENABLE)) {
+		if (xdbc_handle_external_reset()) {
+			xdbc_trace("failed to recover connection\n");
+			return;
+		}
+	}
+
+	/* Handle configure-exit event: */
+	reg = readl(&xdbc.xdbc_reg->control);
+	if (reg & CTRL_DBC_RUN_CHANGE) {
+		writel(reg, &xdbc.xdbc_reg->control);
+		if (reg & CTRL_DBC_RUN)
+			xdbc.flags |= XDBC_FLAGS_CONFIGURED;
+		else
+			xdbc.flags &= ~XDBC_FLAGS_CONFIGURED;
+	}
+
+	/* Handle endpoint stall event: */
+	reg = readl(&xdbc.xdbc_reg->control);
+	if (reg & CTRL_HALT_IN_TR) {
+		xdbc.flags |= XDBC_FLAGS_IN_STALL;
+	} else {
+		xdbc.flags &= ~XDBC_FLAGS_IN_STALL;
+		if (!(xdbc.flags & XDBC_FLAGS_IN_PROCESS))
+			xdbc_bulk_transfer(NULL, XDBC_MAX_PACKET, true);
+	}
+
+	if (reg & CTRL_HALT_OUT_TR)
+		xdbc.flags |= XDBC_FLAGS_OUT_STALL;
+	else
+		xdbc.flags &= ~XDBC_FLAGS_OUT_STALL;
+
+	/* Handle the events in the event ring: */
+	evt_trb = xdbc.evt_ring.dequeue;
+	while ((le32_to_cpu(evt_trb->field[3]) & TRB_CYCLE) == xdbc.evt_ring.cycle_state) {
+		/*
+		 * Add a barrier between reading the cycle flag and any
+		 * reads of the event's flags/data below:
+		 */
+		rmb();
+
+		switch ((le32_to_cpu(evt_trb->field[3]) & TRB_TYPE_BITMASK)) {
+		case TRB_TYPE(TRB_PORT_STATUS):
+			xdbc_handle_port_status(evt_trb);
+			break;
+		case TRB_TYPE(TRB_TRANSFER):
+			xdbc_handle_tx_event(evt_trb);
+			break;
+		default:
+			break;
+		}
+
+		++(xdbc.evt_ring.dequeue);
+		if (xdbc.evt_ring.dequeue == &xdbc.evt_seg.trbs[TRBS_PER_SEGMENT]) {
+			xdbc.evt_ring.dequeue = xdbc.evt_seg.trbs;
+			xdbc.evt_ring.cycle_state ^= 1;
+		}
+
+		evt_trb = xdbc.evt_ring.dequeue;
+		update_erdp = true;
+	}
+
+	/* Update event ring dequeue pointer: */
+	if (update_erdp)
+		xdbc_write64(__pa(xdbc.evt_ring.dequeue), &xdbc.xdbc_reg->erdp);
+}
+
+static int xdbc_bulk_write(const char *bytes, int size)
+{
+	int ret, timeout = 0;
+	unsigned long flags;
+
+retry:
+	if (in_nmi()) {
+		if (!raw_spin_trylock_irqsave(&xdbc.lock, flags))
+			return -EAGAIN;
+	} else {
+		raw_spin_lock_irqsave(&xdbc.lock, flags);
+	}
+
+	xdbc_handle_events();
+
+	/* Check completion of the previous request: */
+	if ((xdbc.flags & XDBC_FLAGS_OUT_PROCESS) && (timeout < 2000000)) {
+		raw_spin_unlock_irqrestore(&xdbc.lock, flags);
+		udelay(100);
+		timeout += 100;
+		goto retry;
+	}
+
+	if (xdbc.flags & XDBC_FLAGS_OUT_PROCESS) {
+		raw_spin_unlock_irqrestore(&xdbc.lock, flags);
+		xdbc_trace("previous transfer not completed yet\n");
+
+		return -ETIMEDOUT;
+	}
+
+	ret = xdbc_bulk_transfer((void *)bytes, size, false);
+	raw_spin_unlock_irqrestore(&xdbc.lock, flags);
+
+	return ret;
+}
+
+static void early_xdbc_write(struct console *con, const char *str, u32 n)
+{
+	static char buf[XDBC_MAX_PACKET];
+	int chunk, ret;
+	int use_cr = 0;
+
+	if (!xdbc.xdbc_reg)
+		return;
+	memset(buf, 0, XDBC_MAX_PACKET);
+	while (n > 0) {
+		for (chunk = 0; chunk < XDBC_MAX_PACKET && n > 0; str++, chunk++, n--) {
+
+			if (!use_cr && *str == '\n') {
+				use_cr = 1;
+				buf[chunk] = '\r';
+				str--;
+				n++;
+				continue;
+			}
+
+			if (use_cr)
+				use_cr = 0;
+			buf[chunk] = *str;
+		}
+
+		if (chunk > 0) {
+			ret = xdbc_bulk_write(buf, chunk);
+			if (ret < 0)
+				xdbc_trace("missed message {%s}\n", buf);
+		}
+	}
+}
+
+static struct console early_xdbc_console = {
+	.name		= "earlyxdbc",
+	.write		= early_xdbc_write,
+	.flags		= CON_PRINTBUFFER,
+	.index		= -1,
+};
+
+void __init early_xdbc_register_console(void)
+{
+	if (early_console)
+		return;
+
+	early_console = &early_xdbc_console;
+	if (early_console_keep)
+		early_console->flags &= ~CON_BOOT;
+	else
+		early_console->flags |= CON_BOOT;
+	register_console(early_console);
+}
+
+static void xdbc_unregister_console(void)
+{
+	if (early_xdbc_console.flags & CON_ENABLED)
+		unregister_console(&early_xdbc_console);
+}
+
+static int xdbc_scrub_function(void *ptr)
+{
+	unsigned long flags;
+
+	while (true) {
+		raw_spin_lock_irqsave(&xdbc.lock, flags);
+		xdbc_handle_events();
+
+		if (!(xdbc.flags & XDBC_FLAGS_INITIALIZED)) {
+			raw_spin_unlock_irqrestore(&xdbc.lock, flags);
+			break;
+		}
+
+		raw_spin_unlock_irqrestore(&xdbc.lock, flags);
+		schedule_timeout_interruptible(1);
+	}
+
+	xdbc_unregister_console();
+	writel(0, &xdbc.xdbc_reg->control);
+	xdbc_trace("dbc scrub function exits\n");
+
+	return 0;
+}
+
+static int __init xdbc_init(void)
+{
+	unsigned long flags;
+	void __iomem *base;
+	int ret = 0;
+	u32 offset;
+
+	if (!(xdbc.flags & XDBC_FLAGS_INITIALIZED))
+		return 0;
+
+	/*
+	 * It's time to shut down the DbC, so that the debug
+	 * port can be reused by the host controller:
+	 */
+	if (early_xdbc_console.index == -1 ||
+	    (early_xdbc_console.flags & CON_BOOT)) {
+		xdbc_trace("hardware not used anymore\n");
+		goto free_and_quit;
+	}
+
+	base = ioremap_nocache(xdbc.xhci_start, xdbc.xhci_length);
+	if (!base) {
+		xdbc_trace("failed to remap the io address\n");
+		ret = -ENOMEM;
+		goto free_and_quit;
+	}
+
+	raw_spin_lock_irqsave(&xdbc.lock, flags);
+	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
+	xdbc.xhci_base = base;
+	offset = xhci_find_next_ext_cap(xdbc.xhci_base, 0, XHCI_EXT_CAPS_DEBUG);
+	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
+	raw_spin_unlock_irqrestore(&xdbc.lock, flags);
+
+	kthread_run(xdbc_scrub_function, NULL, "%s", "xdbc");
+
+	return 0;
+
+free_and_quit:
+	xdbc_free_ring(&xdbc.evt_ring);
+	xdbc_free_ring(&xdbc.out_ring);
+	xdbc_free_ring(&xdbc.in_ring);
+	free_bootmem(xdbc.table_dma, PAGE_SIZE);
+	free_bootmem(xdbc.out_dma, PAGE_SIZE);
+	writel(0, &xdbc.xdbc_reg->control);
+	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
+
+	return ret;
+}
+subsys_initcall(xdbc_init);
diff --git a/drivers/usb/early/xhci-dbc.h b/drivers/usb/early/xhci-dbc.h
new file mode 100644
index 000000000000..2df0f6e613fe
--- /dev/null
+++ b/drivers/usb/early/xhci-dbc.h
@@ -0,0 +1,211 @@
+/*
+ * xhci-dbc.h - xHCI debug capability early driver
+ *
+ * Copyright (C) 2016 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __LINUX_XHCI_DBC_H
+#define __LINUX_XHCI_DBC_H
+
+#include <linux/types.h>
+#include <linux/usb/ch9.h>
+
+/*
+ * xHCI Debug Capability Register interfaces:
+ */
+struct xdbc_regs {
+	__le32	capability;
+	__le32	doorbell;
+	__le32	ersts;		/* Event Ring Segment Table Size*/
+	__le32	__reserved_0;	/* 0c~0f reserved bits */
+	__le64	erstba;		/* Event Ring Segment Table Base Address */
+	__le64	erdp;		/* Event Ring Dequeue Pointer */
+	__le32	control;
+	__le32	status;
+	__le32	portsc;		/* Port status and control */
+	__le32	__reserved_1;	/* 2b~28 reserved bits */
+	__le64	dccp;		/* Debug Capability Context Pointer */
+	__le32	devinfo1;	/* Device Descriptor Info Register 1 */
+	__le32	devinfo2;	/* Device Descriptor Info Register 2 */
+};
+
+#define DEBUG_MAX_BURST(p)	(((p) >> 16) & 0xff)
+
+#define CTRL_DBC_RUN		BIT(0)
+#define CTRL_PORT_ENABLE	BIT(1)
+#define CTRL_HALT_OUT_TR	BIT(2)
+#define CTRL_HALT_IN_TR		BIT(3)
+#define CTRL_DBC_RUN_CHANGE	BIT(4)
+#define CTRL_DBC_ENABLE		BIT(31)
+
+#define DCST_DEBUG_PORT(p)	(((p) >> 24) & 0xff)
+
+#define PORTSC_CONN_STATUS	BIT(0)
+#define PORTSC_CONN_CHANGE	BIT(17)
+#define PORTSC_RESET_CHANGE	BIT(21)
+#define PORTSC_LINK_CHANGE	BIT(22)
+#define PORTSC_CONFIG_CHANGE	BIT(23)
+
+/*
+ * xHCI Debug Capability data structures:
+ */
+struct xdbc_trb {
+	__le32 field[4];
+};
+
+struct xdbc_erst_entry {
+	__le64	seg_addr;
+	__le32	seg_size;
+	__le32	__reserved_0;
+};
+
+struct xdbc_info_context {
+	__le64	string0;
+	__le64	manufacturer;
+	__le64	product;
+	__le64	serial;
+	__le32	length;
+	__le32	__reserved_0[7];
+};
+
+struct xdbc_ep_context {
+	__le32	ep_info1;
+	__le32	ep_info2;
+	__le64	deq;
+	__le32	tx_info;
+	__le32	__reserved_0[11];
+};
+
+struct xdbc_context {
+	struct xdbc_info_context	info;
+	struct xdbc_ep_context		out;
+	struct xdbc_ep_context		in;
+};
+
+#define XDBC_INFO_CONTEXT_SIZE		48
+#define XDBC_MAX_STRING_LENGTH		64
+#define XDBC_STRING_MANUFACTURER	"Linux"
+#define XDBC_STRING_PRODUCT		"Remote GDB"
+#define XDBC_STRING_SERIAL		"0001"
+
+struct xdbc_strings {
+	char	string0[XDBC_MAX_STRING_LENGTH];
+	char	manufacturer[XDBC_MAX_STRING_LENGTH];
+	char	product[XDBC_MAX_STRING_LENGTH];
+	char	serial[XDBC_MAX_STRING_LENGTH];
+};
+
+#define XDBC_PROTOCOL		1	/* GNU Remote Debug Command Set */
+#define XDBC_VENDOR_ID		0x1d6b	/* Linux Foundation 0x1d6b */
+#define XDBC_PRODUCT_ID		0x0004	/* __le16 idProduct; device 0004 */
+#define XDBC_DEVICE_REV		0x0010	/* 0.10 */
+
+/*
+ * xHCI Debug Capability software state structures:
+ */
+struct xdbc_segment {
+	struct xdbc_trb		*trbs;
+	dma_addr_t		dma;
+};
+
+#define XDBC_TRBS_PER_SEGMENT	256
+
+struct xdbc_ring {
+	struct xdbc_segment	*segment;
+	struct xdbc_trb		*enqueue;
+	struct xdbc_trb		*dequeue;
+	u32			cycle_state;
+};
+
+#define XDBC_EPID_OUT		2
+#define XDBC_EPID_IN		3
+
+struct xdbc_state {
+	u16			vendor;
+	u16			device;
+	u32			bus;
+	u32			dev;
+	u32			func;
+	void __iomem		*xhci_base;
+	u64			xhci_start;
+	size_t			xhci_length;
+	int			port_number;
+
+	/* DbC register base */
+	struct xdbc_regs __iomem *xdbc_reg;
+
+	/* DbC table page */
+	dma_addr_t		table_dma;
+	void			*table_base;
+
+	/* event ring segment table */
+	dma_addr_t		erst_dma;
+	size_t			erst_size;
+	void			*erst_base;
+
+	/* event ring segments */
+	struct xdbc_ring	evt_ring;
+	struct xdbc_segment	evt_seg;
+
+	/* debug capability contexts */
+	dma_addr_t		dbcc_dma;
+	size_t			dbcc_size;
+	void			*dbcc_base;
+
+	/* descriptor strings */
+	dma_addr_t		string_dma;
+	size_t			string_size;
+	void			*string_base;
+
+	/* bulk OUT endpoint */
+	struct xdbc_ring	out_ring;
+	struct xdbc_segment	out_seg;
+	void			*out_buf;
+	dma_addr_t		out_dma;
+
+	/* bulk IN endpoint */
+	struct xdbc_ring	in_ring;
+	struct xdbc_segment	in_seg;
+	void			*in_buf;
+	dma_addr_t		in_dma;
+
+	u32			flags;
+
+	/* spinlock for early_xdbc_write() reentrancy */
+	raw_spinlock_t		lock;
+};
+
+#define XDBC_PCI_MAX_BUSES	256
+#define XDBC_PCI_MAX_DEVICES	32
+#define XDBC_PCI_MAX_FUNCTION	8
+
+#define XDBC_TABLE_ENTRY_SIZE	64
+#define XDBC_ERST_ENTRY_NUM	1
+#define XDBC_DBCC_ENTRY_NUM	3
+#define XDBC_STRING_ENTRY_NUM	4
+
+/* Bits definitions for xdbc_state.flags: */
+#define XDBC_FLAGS_INITIALIZED	BIT(0)
+#define XDBC_FLAGS_IN_STALL	BIT(1)
+#define XDBC_FLAGS_OUT_STALL	BIT(2)
+#define XDBC_FLAGS_IN_PROCESS	BIT(3)
+#define XDBC_FLAGS_OUT_PROCESS	BIT(4)
+#define XDBC_FLAGS_CONFIGURED	BIT(5)
+
+#define XDBC_MAX_PACKET		1024
+
+/* Door bell target: */
+#define OUT_EP_DOORBELL		0
+#define IN_EP_DOORBELL		1
+#define DOOR_BELL_TARGET(p)	(((p) & 0xff) << 8)
+
+#define xdbc_read64(regs)	xhci_read_64(NULL, (regs))
+#define xdbc_write64(val, regs)	xhci_write_64(NULL, (val), (regs))
+
+#endif /* __LINUX_XHCI_DBC_H */
diff --git a/drivers/usb/serial/usb_debug.c b/drivers/usb/serial/usb_debug.c
index ca2fa5bbe17e..92f7e5c21162 100644
--- a/drivers/usb/serial/usb_debug.c
+++ b/drivers/usb/serial/usb_debug.c
@@ -32,7 +32,18 @@ static const struct usb_device_id id_table[] = {
 	{ USB_DEVICE(0x0525, 0x127a) },
 	{ },
 };
-MODULE_DEVICE_TABLE(usb, id_table);
+
+static const struct usb_device_id dbc_id_table[] = {
+	{ USB_DEVICE(0x1d6b, 0x0004) },
+	{ },
+};
+
+static const struct usb_device_id id_table_combined[] = {
+	{ USB_DEVICE(0x0525, 0x127a) },
+	{ USB_DEVICE(0x1d6b, 0x0004) },
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, id_table_combined);
 
 /* This HW really does not support a serial break, so one will be
  * emulated when ever the break state is set to true.
@@ -71,9 +82,20 @@ static struct usb_serial_driver debug_device = {
 	.process_read_urb =	usb_debug_process_read_urb,
 };
 
+static struct usb_serial_driver dbc_device = {
+	.driver = {
+		.owner =	THIS_MODULE,
+		.name =		"xhci_dbc",
+	},
+	.id_table =		dbc_id_table,
+	.num_ports =		1,
+	.break_ctl =		usb_debug_break_ctl,
+	.process_read_urb =	usb_debug_process_read_urb,
+};
+
 static struct usb_serial_driver * const serial_drivers[] = {
-	&debug_device, NULL
+	&debug_device, &dbc_device, NULL
 };
 
-module_usb_serial_driver(serial_drivers, id_table);
+module_usb_serial_driver(serial_drivers, id_table_combined);
 MODULE_LICENSE("GPL");
diff --git a/include/linux/usb/xhci-dbgp.h b/include/linux/usb/xhci-dbgp.h
new file mode 100644
index 000000000000..80c1cca1f529
--- /dev/null
+++ b/include/linux/usb/xhci-dbgp.h
@@ -0,0 +1,29 @@
+/*
+ * Standalone xHCI debug capability driver
+ *
+ * Copyright (C) 2016 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu.lu@linux.intel.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __LINUX_XHCI_DBGP_H
+#define __LINUX_XHCI_DBGP_H
+
+#ifdef CONFIG_EARLY_PRINTK_USB_XDBC
+int __init early_xdbc_parse_parameter(char *s);
+int __init early_xdbc_setup_hardware(void);
+void __init early_xdbc_register_console(void);
+#else
+static inline int __init early_xdbc_setup_hardware(void)
+{
+	return -ENODEV;
+}
+static inline void __init early_xdbc_register_console(void)
+{
+}
+#endif /* CONFIG_EARLY_PRINTK_USB_XDBC */
+#endif /* __LINUX_XHCI_DBGP_H */