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* [PATCH v4 0/4] usb: early: add support for early printk through USB3 debug port
@ 2016-11-01  4:59 Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
                   ` (3 more replies)
  0 siblings, 4 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-01  4:59 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: Mathias Nyman, Ingo Molnar, linux-usb, x86, linux-kernel, Lu Baolu

xHCI debug capability (DbC) is an optional but standalone
functionality provided by an xHCI host controller. With DbC
hardware initialized, the system will present a debug device
through the USB3 debug port (normally the first USB3 port).
The debug device is fully compliant with the USB framework
and provides the equivalent of a very high performance (USB3)
full-duplex serial link between the debug host and target.
The DbC functionality is independent of xHCI host. There
isn't any precondition from xHCI host side for DbC to work.

This patch set adds support for early printk functionality
through a USB3 debug port by 1) initializing and enabling
the DbC hardware during early boot; 2) registering a boot
console to the system so that early printk messages can go
through the USB3 debug port. It also includes some lines
of changes in usb_debug driver so that it can be bound when
a USB3 debug device is enumerated.

This code is designed to be used only for kernel debugging
when machine crashes very early before the console code is
initialized. It makes the life of kernel debugging easier
when people work with a modern machine without any legacy
serial ports.

---
Change log:
v3->v4:
  - Rename the document with .dst suffix.
  - Add the list of hardware that has been succesfuly
    tested on in the document.

v2->v3:
  - Removed spinlock usage.
  - Removed work queue usage.
  - Refined the user guide document.

v1->v2:
  - Refactor the duplicate code in xdbc_early_start() and
    xdbc_handle_external_reset().
  - Free resources when hardware not used any more.
  - Refine the user guide document.

Lu Baolu (4):
  usb: dbc: early driver for xhci debug capability
  x86: add support for earlyprintk via USB3 debug port
  usb: serial: usb_debug: add support for dbc debug device
  usb: doc: add document for USB3 debug port usage

 Documentation/kernel-parameters.txt   |    1 +
 Documentation/usb/usb3-debug-port.rst |   95 +++
 arch/x86/Kconfig.debug                |   14 +
 arch/x86/kernel/early_printk.c        |    5 +
 arch/x86/kernel/setup.c               |    7 +
 drivers/usb/Kconfig                   |    3 +
 drivers/usb/Makefile                  |    2 +-
 drivers/usb/early/Makefile            |    1 +
 drivers/usb/early/xhci-dbc.c          | 1050 +++++++++++++++++++++++++++++++++
 drivers/usb/early/xhci-dbc.h          |  202 +++++++
 drivers/usb/serial/usb_debug.c        |   28 +-
 include/linux/usb/xhci-dbgp.h         |   22 +
 12 files changed, 1426 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/usb/usb3-debug-port.rst
 create mode 100644 drivers/usb/early/xhci-dbc.c
 create mode 100644 drivers/usb/early/xhci-dbc.h
 create mode 100644 include/linux/usb/xhci-dbgp.h

-- 
2.1.4

^ permalink raw reply	[flat|nested] 17+ messages in thread

* [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-01  4:59 [PATCH v4 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
@ 2016-11-01  4:59 ` Lu Baolu
  2016-11-09  9:23   ` Thomas Gleixner
  2016-11-09  9:37   ` Thomas Gleixner
  2016-11-01  4:59 ` [PATCH v4 2/4] x86: add support for earlyprintk via USB3 debug port Lu Baolu
                   ` (2 subsequent siblings)
  3 siblings, 2 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-01  4:59 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: Mathias Nyman, Ingo Molnar, linux-usb, x86, linux-kernel, Lu Baolu

xHCI debug capability (DbC) is an optional but standalone
functionality provided by an xHCI host controller. Software
learns this capability by walking through the extended
capability list of the host. xHCI specification describes
DbC in section 7.6.

This patch introduces the code to probe and initialize the
debug capability hardware during early boot. With hardware
initialized, the debug target (system on which this code is
running) will present a debug device through the debug port
(normally the first USB3 port). The debug device is fully
compliant with the USB framework and provides the equivalent
of a very high performance (USB3) full-duplex serial link
between the debug host and target. The DbC functionality is
independent of xHCI host. There isn't any precondition from
xHCI host side for DbC to work.

This patch also includes bulk out and bulk in interfaces.
These interfaces could be used to implement early printk
bootconsole or hook to various system debuggers.

This code is designed to be only used for kernel debugging
when machine crashes very early before the console code is
initialized. For normal operation it is not recommended.

Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 arch/x86/Kconfig.debug        |   14 +
 drivers/usb/Kconfig           |    3 +
 drivers/usb/Makefile          |    2 +-
 drivers/usb/early/Makefile    |    1 +
 drivers/usb/early/xhci-dbc.c  | 1050 +++++++++++++++++++++++++++++++++++++++++
 drivers/usb/early/xhci-dbc.h  |  202 ++++++++
 include/linux/usb/xhci-dbgp.h |   22 +
 7 files changed, 1293 insertions(+), 1 deletion(-)
 create mode 100644 drivers/usb/early/xhci-dbc.c
 create mode 100644 drivers/usb/early/xhci-dbc.h
 create mode 100644 include/linux/usb/xhci-dbgp.h

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 67eec55..13e85b7 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -29,6 +29,7 @@ config EARLY_PRINTK
 config EARLY_PRINTK_DBGP
 	bool "Early printk via EHCI debug port"
 	depends on EARLY_PRINTK && PCI
+	select USB_EARLY_PRINTK
 	---help---
 	  Write kernel log output directly into the EHCI debug port.
 
@@ -48,6 +49,19 @@ 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_XDBC
+	bool "Early printk via xHCI debug port"
+	depends on EARLY_PRINTK && PCI
+	select USB_EARLY_PRINTK
+	---help---
+	  Write kernel log output directly into the xHCI 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,
+	  unless you want to debug such a crash.
+
 config X86_PTDUMP_CORE
 	def_bool n
 
diff --git a/drivers/usb/Kconfig b/drivers/usb/Kconfig
index fbe493d..9313fff 100644
--- a/drivers/usb/Kconfig
+++ b/drivers/usb/Kconfig
@@ -19,6 +19,9 @@ config USB_EHCI_BIG_ENDIAN_MMIO
 config USB_EHCI_BIG_ENDIAN_DESC
 	bool
 
+config USB_EARLY_PRINTK
+	bool
+
 menuconfig USB_SUPPORT
 	bool "USB support"
 	depends on HAS_IOMEM
diff --git a/drivers/usb/Makefile b/drivers/usb/Makefile
index 7791af6..0c37838 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_USB_EARLY_PRINTK)	+= early/
 
 obj-$(CONFIG_USB_ATM)		+= atm/
 obj-$(CONFIG_USB_SPEEDTOUCH)	+= atm/
diff --git a/drivers/usb/early/Makefile b/drivers/usb/early/Makefile
index 24bbe51..2db5906 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_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 0000000..728a1a0
--- /dev/null
+++ b/drivers/usb/early/xhci-dbc.c
@@ -0,0 +1,1050 @@
+/**
+ * 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 "../host/xhci.h"
+#include "xhci-dbc.h"
+
+static struct xdbc_state xdbc;
+static int early_console_keep;
+
+#ifdef XDBC_TRACE
+#define	xdbc_trace	trace_printk
+#else
+static inline void xdbc_trace(const char *fmt, ...) { }
+#endif /* XDBC_TRACE */
+
+static int xdbc_bulk_transfer(void *data, int size, bool read);
+
+static void __iomem * __init xdbc_map_pci_mmio(u32 bus, u32 dev, u32 func)
+{
+	u32 val, sz;
+	u64 val64, sz64, mask64;
+	u8 byte;
+	void __iomem *base;
+
+	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 = (u32)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 |= ((u64)~0 << 32);
+	}
+
+	sz64 &= mask64;
+
+	if (sizeof(dma_addr_t) < 8 || !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 void xdbc_early_delay(unsigned long count)
+{
+	u8 val;
+
+	val = inb(0x80);
+	while (count-- > 0)
+		outb(val, 0x80);
+}
+
+static void xdbc_runtime_delay(unsigned long count)
+{
+	udelay(count);
+}
+
+static void (*xdbc_delay)(unsigned long) = xdbc_early_delay;
+
+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;
+		xdbc_delay(delay);
+		wait -= delay;
+	} while (wait > 0);
+
+	return -ETIMEDOUT;
+}
+
+static void __init xdbc_bios_handoff(void)
+{
+	int ext_cap_offset;
+	int timeout;
+	u32 val;
+
+	ext_cap_offset = xhci_find_next_ext_cap(xdbc.xhci_base,
+						0, XHCI_EXT_CAPS_LEGACY);
+	val = readl(xdbc.xhci_base + ext_cap_offset);
+
+	/* If the BIOS owns the HC, signal that the OS wants it, and wait */
+	if (val & XHCI_HC_BIOS_OWNED) {
+		writel(val | XHCI_HC_OS_OWNED,
+		       xdbc.xhci_base + ext_cap_offset);
+		timeout = handshake(xdbc.xhci_base + ext_cap_offset,
+				    XHCI_HC_BIOS_OWNED, 0, 5000, 10);
+
+		/* Assume a buggy BIOS and take HC ownership anyway */
+		if (timeout) {
+			pr_notice("xHCI BIOS handoff failed\n");
+			writel(val & ~XHCI_HC_BIOS_OWNED,
+			       xdbc.xhci_base + ext_cap_offset);
+		}
+	}
+
+	/* Disable any BIOS SMIs and clear all SMI events*/
+	val = readl(xdbc.xhci_base + ext_cap_offset +
+		    XHCI_LEGACY_CONTROL_OFFSET);
+	val &= XHCI_LEGACY_DISABLE_SMI;
+	val |= XHCI_LEGACY_SMI_EVENTS;
+	writel(val, xdbc.xhci_base + ext_cap_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_trb *link_trb;
+	struct xdbc_segment *seg = ring->segment;
+
+	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_erst_entry *entry;
+	struct xdbc_strings *strings;
+	struct xdbc_context *context;
+	struct xdbc_ep_context *ep_in, *ep_out;
+	struct usb_string_descriptor *s_desc;
+	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;
+
+	/* Initialize Event Ring Segment Table */
+	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->rsvd = 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 */
+	BUILD_BUG_ON(sizeof(struct xdbc_info_context) != 64);
+	BUILD_BUG_ON(sizeof(struct xdbc_ep_context) != 64);
+	BUILD_BUG_ON(sizeof(struct xdbc_context) != 64 * 3);
+
+	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;
+
+	/* 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;
+	index += XDBC_STRING_ENTRY_NUM;
+
+	strings = (struct xdbc_strings *)xdbc.string_base;
+
+	/* 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->manufacture;
+	s_desc->bLength = (strlen(XDBC_STRING_MANUFACTURE) + 1) * 2;
+	s_desc->bDescriptorType = USB_DT_STRING;
+	xdbc_put_utf16(s_desc->wData, XDBC_STRING_MANUFACTURE,
+		       strlen(XDBC_STRING_MANUFACTURE));
+
+	string_length += s_desc->bLength;
+	string_length <<= 8;
+
+	/* string 0 */
+	strings->string0[0] = 4;
+	strings->string0[1] = USB_DT_STRING;
+	strings->string0[2] = 0x09;
+	strings->string0[3] = 0x04;
+
+	string_length += 4;
+
+	/* populate the contexts */
+	context = (struct xdbc_context *)xdbc.dbcc_base;
+	context->info.string0 = cpu_to_le64(xdbc.string_dma);
+	context->info.manufacture = cpu_to_le64(xdbc.string_dma +
+			XDBC_MAX_STRING_LENGTH);
+	context->info.product = cpu_to_le64(xdbc.string_dma +
+			XDBC_MAX_STRING_LENGTH * 2);
+	context->info.serial = cpu_to_le64(xdbc.string_dma +
+			XDBC_MAX_STRING_LENGTH * 3);
+	context->info.length = cpu_to_le32(string_length);
+
+	max_burst = DEBUG_MAX_BURST(readl(&xdbc.xdbc_reg->control));
+	ep_out = (struct xdbc_ep_context *)&context->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);
+
+	ep_in = (struct xdbc_ep_context *)&context->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);
+
+	/* write DbC context pointer register */
+	xdbc_write64(xdbc.dbcc_dma, &xdbc.xdbc_reg->dccp);
+
+	/* device descriptor info registers */
+	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)
+{
+	u32 val, cap_length;
+	void __iomem *ops_reg;
+	void __iomem *portsc;
+	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);
+		/* reset the port if CCS bit is cleared */
+		if (!(val & PORT_CONNECT))
+			writel(val | PORT_RESET, portsc);
+	}
+}
+
+static void __init xdbc_reset_debug_port(void)
+{
+	int offset = 0;
+	u32 val, port_offset, port_count;
+
+	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_DCE | CTRL_PED, &xdbc.xdbc_reg->control);
+	ret = handshake(&xdbc.xdbc_reg->control,
+			CTRL_DCE, CTRL_DCE, 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_CCS, PORTSC_CCS, 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_DCR, CTRL_DCR, 5000000, 100);
+	if (ret) {
+		xdbc_trace("waiting for device configuration timed out\n");
+		return ret;
+	}
+
+	/* port should have a valid port# */
+	status = readl(&xdbc.xdbc_reg->status);
+	if (!DCST_DPN(status)) {
+		xdbc_trace("invalid root hub port number\n");
+		return -ENODEV;
+	}
+
+	xdbc.port_number = DCST_DPN(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_handle_external_reset(void)
+{
+	int ret = 0;
+	static int failure_count;
+
+	xdbc_trace("external reset detected\n");
+
+	if (failure_count >= 5)
+		return -ENODEV;
+
+	xdbc.flags = 0;
+	writel(0, &xdbc.xdbc_reg->control);
+	ret = handshake(&xdbc.xdbc_reg->control, CTRL_DCE, 0, 100000, 10);
+	if (ret)
+		goto count_and_out;
+
+	xdbc_mem_init();
+
+	mmiowb();
+
+	ret = xdbc_start();
+	if (ret < 0)
+		goto count_and_out;
+
+	xdbc_trace("dbc recovered\n");
+
+	xdbc.flags |= XDBC_FLAGS_INITIALIZED | XDBC_FLAGS_CONFIGURED;
+
+	xdbc_bulk_transfer(NULL, XDBC_MAX_PACKET, true);
+
+	return 0;
+
+count_and_out:
+	failure_count++;
+	xdbc_trace("failed to recover from external reset, retried %d\n",
+		   failure_count);
+	return ret;
+}
+
+static int xdbc_bulk_transfer(void *data, int size, bool read)
+{
+	u64 addr;
+	u32 length, control;
+	struct xdbc_trb *trb;
+	struct xdbc_ring *ring;
+	u32 cycle;
+	int ret;
+
+	if (size > XDBC_MAX_PACKET) {
+		xdbc_trace("oops: bad parameter, size %d\n", size);
+		return -EINVAL;
+	}
+
+	if (!(readl(&xdbc.xdbc_reg->control) & CTRL_DCE)) {
+		ret = xdbc_handle_external_reset();
+		if (ret) {
+			xdbc_trace("oops: hardware failed to recover\n");
+			return -EIO;
+		}
+	}
+
+	if (!(xdbc.flags & XDBC_FLAGS_INITIALIZED) ||
+	    !(xdbc.flags & XDBC_FLAGS_CONFIGURED) ||
+	    (!read && (xdbc.flags & XDBC_FLAGS_BULKOUT_STALL)) ||
+	    (read && (xdbc.flags & XDBC_FLAGS_BULKIN_STALL))) {
+		xdbc_trace("oops: hardware not ready %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);
+
+	/*
+	 * Memory barrier to ensure hardware sees the trbs
+	 * enqueued above.
+	 */
+	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 __init xdbc_early_setup(void)
+{
+	int ret;
+
+	writel(0, &xdbc.xdbc_reg->control);
+	ret = handshake(&xdbc.xdbc_reg->control, CTRL_DCE, 0, 100000, 100);
+	if (ret)
+		return ret;
+
+	/* allocate 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 event ring */
+	ret = xdbc_alloc_ring(&xdbc.evt_seg, &xdbc.evt_ring);
+	if (ret < 0)
+		return ret;
+
+	/* IN/OUT endpoint transfer ring */
+	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();
+
+	/*
+	 * Memory barrier to ensure hardware sees the bits
+	 * setting above.
+	 */
+	mmiowb();
+
+	ret = xdbc_start();
+	if (ret < 0) {
+		/* give the shared port back to host */
+		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 = 1;
+
+	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("no host controller found in your system\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("DbC wasn't found in your host controller\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;
+
+	/* hand over the owner of host from BIOS */
+	xdbc_bios_handoff();
+
+	ret = xdbc_early_setup();
+	if (ret) {
+		pr_notice("failed to setup DbC hardware\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_CSC) {
+		xdbc_trace("%s: connect status change event\n", __func__);
+		writel(port_reg | PORTSC_CSC, &xdbc.xdbc_reg->portsc);
+		port_reg = readl(&xdbc.xdbc_reg->portsc);
+	}
+
+	if (port_reg & PORTSC_PRC) {
+		xdbc_trace("%s: port reset change event\n", __func__);
+		writel(port_reg | PORTSC_PRC, &xdbc.xdbc_reg->portsc);
+		port_reg = readl(&xdbc.xdbc_reg->portsc);
+	}
+
+	if (port_reg & PORTSC_PLC) {
+		xdbc_trace("%s: port link status change event\n", __func__);
+		writel(port_reg | PORTSC_PLC, &xdbc.xdbc_reg->portsc);
+		port_reg = readl(&xdbc.xdbc_reg->portsc);
+	}
+
+	if (port_reg & PORTSC_CEC) {
+		xdbc_trace("%s: config error change\n", __func__);
+		writel(port_reg | PORTSC_CEC, &xdbc.xdbc_reg->portsc);
+		port_reg = readl(&xdbc.xdbc_reg->portsc);
+	}
+}
+
+static void xdbc_handle_tx_event(struct xdbc_trb *evt_trb)
+{
+	u32 comp_code;
+	size_t remain_length;
+	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]));
+
+	/*
+	 * Possible Completion Codes for DbC Transfer Event are Success,
+	 * Stall Error, USB Transaction Error, Babble Detected Error,
+	 * TRB Error, Short Packet, Undefined Error, Event Ring Full Error,
+	 * and Vendor Defined Error. TRB error, undefined error and vendor
+	 * defined error will result in HOT/HIT set and be handled the same
+	 * way as Stall error.
+	 */
+	switch (comp_code) {
+	case COMP_SUCCESS:
+		remain_length = 0;
+	case COMP_SHORT_TX:
+		xdbc_trace("%s: endpoint %d remains %ld bytes\n", __func__,
+			   ep_id, remain_length);
+		break;
+	case COMP_TRB_ERR:
+	case COMP_BABBLE:
+	case COMP_TX_ERR:
+	case COMP_STALL:
+	default:
+		if (ep_id == XDBC_EPID_OUT)
+			xdbc.flags |= XDBC_FLAGS_BULKOUT_STALL;
+		if (ep_id == XDBC_EPID_IN)
+			xdbc.flags |= XDBC_FLAGS_BULKIN_STALL;
+
+		xdbc_trace("%s: endpoint %d stalled\n", __func__, 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("%s: invalid endpoint id %d\n", __func__, ep_id);
+	}
+}
+
+static void xdbc_handle_events(void)
+{
+	struct xdbc_trb *evt_trb;
+	bool update_erdp = false;
+	u8 command;
+	u32 reg;
+
+	command = read_pci_config_byte(xdbc.bus, xdbc.dev,
+				       xdbc.func, PCI_COMMAND);
+	if (!(command & PCI_COMMAND_MASTER)) {
+		command |= PCI_COMMAND_MASTER | PCI_COMMAND_MEMORY;
+		write_pci_config_byte(xdbc.bus, xdbc.dev,
+				      xdbc.func, PCI_COMMAND, command);
+	}
+
+	/* check and handle configure-exit event */
+	reg = readl(&xdbc.xdbc_reg->control);
+	if (reg & CTRL_DRC) {
+		xdbc.flags &= ~XDBC_FLAGS_CONFIGURED;
+		writel(reg | CTRL_DRC, &xdbc.xdbc_reg->control);
+	} else {
+		xdbc.flags |= XDBC_FLAGS_CONFIGURED;
+	}
+
+	/* check endpoint stall event */
+	reg = readl(&xdbc.xdbc_reg->control);
+	if (reg & CTRL_HIT) {
+		xdbc.flags |= XDBC_FLAGS_BULKIN_STALL;
+	} else {
+		xdbc.flags &= ~XDBC_FLAGS_BULKIN_STALL;
+		if (!(xdbc.flags & XDBC_FLAGS_IN_PROCESS))
+			xdbc_bulk_transfer(NULL, XDBC_MAX_PACKET, true);
+	}
+
+	if (reg & CTRL_HOT)
+		xdbc.flags |= XDBC_FLAGS_BULKOUT_STALL;
+	else
+		xdbc.flags &= ~XDBC_FLAGS_BULKOUT_STALL;
+
+	evt_trb = xdbc.evt_ring.dequeue;
+	while ((le32_to_cpu(evt_trb->field[3]) & TRB_CYCLE) ==
+			xdbc.evt_ring.cycle_state) {
+		/*
+		 * Memory barrier to ensure software sees the trbs
+		 * enqueued by hardware.
+		 */
+		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;
+		}
+
+		/* advance to the next trb */
+		++(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;
+
+	xdbc_handle_events();
+
+	/* Check completion of the previous request. */
+	while (xdbc.flags & XDBC_FLAGS_OUT_PROCESS) {
+		if (timeout > 1000000)
+			break;
+
+		xdbc_delay(100);
+		timeout += 100;
+		xdbc_handle_events();
+	}
+
+	if (xdbc.flags & XDBC_FLAGS_OUT_PROCESS) {
+		/*
+		 * Oops, hardware wasn't able to complete the
+		 * previous transfer.
+		 */
+		xdbc_trace("oops: previous transfer not completed yet\n");
+
+		return -ETIMEDOUT;
+	}
+
+	ret = xdbc_bulk_transfer((void *)bytes, size, false);
+
+	return ret;
+}
+
+static void early_xdbc_write(struct console *con, const char *str, u32 n)
+{
+	int chunk, ret;
+	static char buf[XDBC_MAX_PACKET];
+	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)
+				break;
+		}
+	}
+}
+
+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 int __init xdbc_init(void)
+{
+	void __iomem *base;
+	u32 offset;
+	int ret = 0;
+
+	if (!(xdbc.flags & XDBC_FLAGS_INITIALIZED))
+		return 0;
+
+	xdbc_delay = xdbc_runtime_delay;
+
+	/*
+	 * It's time to shutdown DbC, so that the debug
+	 * port could be reused by the host controller.
+	 */
+	if (early_xdbc_console.index == -1 ||
+	    (early_xdbc_console.flags & CON_BOOT)) {
+		xdbc_trace("hardware not used any more\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;
+	}
+
+	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
+	xdbc_trace("early mapped IO address released\n");
+
+	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);
+
+	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 0000000..9a4f0f7
--- /dev/null
+++ b/drivers/usb/early/xhci-dbc.h
@@ -0,0 +1,202 @@
+/*
+ * 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>
+
+/**
+ * struct xdbc_regs - xHCI Debug Capability Register interface.
+ */
+struct xdbc_regs {
+	__le32	capability;
+	__le32	doorbell;
+	__le32	ersts;		/* Event Ring Segment Table Size*/
+	__le32	rvd0;		/* 0c~0f reserved bits */
+	__le64	erstba;		/* Event Ring Segment Table Base Address */
+	__le64	erdp;		/* Event Ring Dequeue Pointer */
+	__le32	control;
+#define	DEBUG_MAX_BURST(p)	(((p) >> 16) & 0xff)
+#define	CTRL_DCR		BIT(0)		/* DbC Run */
+#define	CTRL_PED		BIT(1)		/* Port Enable/Disable */
+#define	CTRL_HOT		BIT(2)		/* Halt Out TR */
+#define	CTRL_HIT		BIT(3)		/* Halt In TR */
+#define	CTRL_DRC		BIT(4)		/* DbC run change */
+#define	CTRL_DCE		BIT(31)		/* DbC enable */
+	__le32	status;
+#define	DCST_DPN(p)		(((p) >> 24) & 0xff)
+	__le32	portsc;		/* Port status and control */
+#define	PORTSC_CCS		BIT(0)
+#define	PORTSC_CSC		BIT(17)
+#define	PORTSC_PRC		BIT(21)
+#define	PORTSC_PLC		BIT(22)
+#define	PORTSC_CEC		BIT(23)
+	__le32	rvd1;		/* 2b~28 reserved bits */
+	__le64	dccp;		/* Debug Capability Context Pointer */
+	__le32	devinfo1;	/* Device Descriptor Info Register 1 */
+	__le32	devinfo2;	/* Device Descriptor Info Register 2 */
+};
+
+/*
+ * xHCI Debug Capability data structures
+ */
+struct xdbc_trb {
+	__le32 field[4];
+};
+
+struct xdbc_erst_entry {
+	__le64	seg_addr;
+	__le32	seg_size;
+	__le32	rsvd;
+};
+
+struct xdbc_info_context {
+	__le64	string0;
+	__le64	manufacture;
+	__le64	product;
+	__le64	serial;
+	__le32	length;
+	__le32	rsvdz[7];
+};
+
+struct xdbc_ep_context {
+	__le32	ep_info1;
+	__le32	ep_info2;
+	__le64	deq;
+	__le32	tx_info;
+	__le32	rsvd0[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_MANUFACTURE		"Linux"
+#define	XDBC_STRING_PRODUCT		"Remote GDB"
+#define	XDBC_STRING_SERIAL		"0001"
+struct xdbc_strings {
+	char	string0[XDBC_MAX_STRING_LENGTH];
+	char	manufacture[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 */
+
+/*
+ * software state structure
+ */
+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 {
+	/* pci device info*/
+	u16		vendor;
+	u16		device;
+	u32		bus;
+	u32		dev;
+	u32		func;
+	void __iomem	*xhci_base;
+	u64		xhci_start;
+	size_t		xhci_length;
+	int		port_number;
+#define	XDBC_PCI_MAX_BUSES		256
+#define	XDBC_PCI_MAX_DEVICES		32
+#define	XDBC_PCI_MAX_FUNCTION		8
+
+	/* DbC register base */
+	struct		xdbc_regs __iomem *xdbc_reg;
+
+	/* DbC table page */
+	dma_addr_t	table_dma;
+	void		*table_base;
+
+#define	XDBC_TABLE_ENTRY_SIZE		64
+#define	XDBC_ERST_ENTRY_NUM		1
+#define	XDBC_DBCC_ENTRY_NUM		3
+#define	XDBC_STRING_ENTRY_NUM		4
+
+	/* 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;
+#define XDBC_FLAGS_INITIALIZED		BIT(0)
+#define XDBC_FLAGS_BULKIN_STALL		BIT(1)
+#define XDBC_FLAGS_BULKOUT_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/include/linux/usb/xhci-dbgp.h b/include/linux/usb/xhci-dbgp.h
new file mode 100644
index 0000000..aa9441f
--- /dev/null
+++ b/include/linux/usb/xhci-dbgp.h
@@ -0,0 +1,22 @@
+/*
+ * 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_XDBC
+int __init early_xdbc_parse_parameter(char *s);
+int __init early_xdbc_setup_hardware(void);
+void __init early_xdbc_register_console(void);
+#endif /* CONFIG_EARLY_PRINTK_XDBC */
+
+#endif /* __LINUX_XHCI_DBGP_H */
-- 
2.1.4

^ permalink raw reply related	[flat|nested] 17+ messages in thread

* [PATCH v4 2/4] x86: add support for earlyprintk via USB3 debug port
  2016-11-01  4:59 [PATCH v4 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
@ 2016-11-01  4:59 ` Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 3/4] usb: serial: usb_debug: add support for dbc debug device Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 4/4] usb: doc: add document for USB3 debug port usage Lu Baolu
  3 siblings, 0 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-01  4:59 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: Mathias Nyman, Ingo Molnar, linux-usb, x86, linux-kernel, Lu Baolu

Add support for early printk by writing debug messages to the
USB3 debug port.   Users can use this type of early printk by
specifying kernel parameter of "earlyprintk=xdbc". This gives
users a chance of providing debug output.

The hardware for USB3 debug port requires DMA memory blocks.
This requires to delay setting up debugging hardware and
registering boot console until the memblocks are filled.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: x86@kernel.org
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 Documentation/kernel-parameters.txt | 1 +
 arch/x86/kernel/early_printk.c      | 5 +++++
 arch/x86/kernel/setup.c             | 7 +++++++
 3 files changed, 13 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 37babf9..99b64b3 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1178,6 +1178,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			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/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 8a12199..c4031b9 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_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 9c337b0..09d4a56 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -70,6 +70,8 @@
 #include <linux/tboot.h>
 #include <linux/jiffies.h>
 
+#include <linux/usb/xhci-dbgp.h>
+
 #include <video/edid.h>
 
 #include <asm/mtrr.h>
@@ -1096,6 +1098,11 @@ void __init setup_arch(char **cmdline_p)
 	memblock_set_current_limit(ISA_END_ADDRESS);
 	memblock_x86_fill();
 
+#ifdef CONFIG_EARLY_PRINTK_XDBC
+	if (!early_xdbc_setup_hardware())
+		early_xdbc_register_console();
+#endif
+
 	reserve_bios_regions();
 
 	if (efi_enabled(EFI_MEMMAP)) {
-- 
2.1.4

^ permalink raw reply related	[flat|nested] 17+ messages in thread

* [PATCH v4 3/4] usb: serial: usb_debug: add support for dbc debug device
  2016-11-01  4:59 [PATCH v4 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 2/4] x86: add support for earlyprintk via USB3 debug port Lu Baolu
@ 2016-11-01  4:59 ` Lu Baolu
  2016-11-01  4:59 ` [PATCH v4 4/4] usb: doc: add document for USB3 debug port usage Lu Baolu
  3 siblings, 0 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-01  4:59 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: Mathias Nyman, Ingo Molnar, linux-usb, x86, linux-kernel, Lu Baolu

This patch add dbc debug device support in usb_debug driver.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/usb_debug.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/usb_debug.c b/drivers/usb/serial/usb_debug.c
index ca2fa5b..92f7e5c 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");
-- 
2.1.4

^ permalink raw reply related	[flat|nested] 17+ messages in thread

* [PATCH v4 4/4] usb: doc: add document for USB3 debug port usage
  2016-11-01  4:59 [PATCH v4 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
                   ` (2 preceding siblings ...)
  2016-11-01  4:59 ` [PATCH v4 3/4] usb: serial: usb_debug: add support for dbc debug device Lu Baolu
@ 2016-11-01  4:59 ` Lu Baolu
  3 siblings, 0 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-01  4:59 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: Mathias Nyman, Ingo Molnar, linux-usb, x86, linux-kernel,
	Lu Baolu, linux-doc

Add Documentation/usb/usb3-debug-port.rst. This document includes
the user guide for USB3 debug port.

Cc: linux-doc@vger.kernel.org
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 Documentation/usb/usb3-debug-port.rst | 95 +++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 Documentation/usb/usb3-debug-port.rst

diff --git a/Documentation/usb/usb3-debug-port.rst b/Documentation/usb/usb3-debug-port.rst
new file mode 100644
index 0000000..70eabe4
--- /dev/null
+++ b/Documentation/usb/usb3-debug-port.rst
@@ -0,0 +1,95 @@
+===============
+USB3 debug port
+===============
+
+:Author: Lu Baolu <baolu.lu@linux.intel.com>
+:Date: October 2016
+
+GENERAL
+=======
+
+This is a HOWTO for using USB3 debug port on x86 systems.
+
+Before using any kernel debugging functionalities based on USB3
+debug port, you need to check 1) whether debug port is supported
+by the xHCI host, 2) which port is used for debugging purpose
+(normally the first USB3 root port). You must have a USB 3.0
+super-speed A-to-A debugging cable to connect the debug target
+with a debug host. In this document, a debug target stands for
+the system under debugging; while, a debug host stands for a
+stand-alone system that is able to talk to the debugging target
+through the USB3 debug port.
+
+EARLY PRINTK
+============
+
+On debug target system, you need to customize a debugging kernel
+with CONFIG_EARLY_PRINTK_XDBC enabled. And add below kernel boot
+parameter::
+
+	"earlyprintk=xdbc"
+
+If there are multiple xHCI controllers in the system, you can
+append a host contoller index to this kernel parameter. This
+index is started from 0.
+
+If you are going to leverage the keep option defined by the
+early printk framework to keep the boot console alive after
+early boot, you'd better add below kernel boot parameter::
+
+	"usbcore.autosuspend=-1"
+
+On debug host side, you don't need to customize the kernel, but
+you need to disable usb subsystem runtime power management by
+adding below kernel boot parameter::
+
+	"usbcore.autosuspend=-1"
+
+Before starting the debug target, you should connect the debug
+port on debug target with a 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 debug target, DbC (the debug engine for USB3
+debug port) hardware gets initialized. Debug host should be able
+to enumerate the debug target as a debug device. Debug host will
+then bind the debug device with the usb_debug driver module and
+create the /dev/ttyUSB0 device.
+
+If device enumeration goes smoothly, you should be able to see
+below kernel messages on 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 run below bash scripts on debug host to read the kernel
+log sent from debug target.
+
+.. code-block:: sh
+
+	===== start of bash scripts =============
+	#!/bin/bash
+
+	while true ; do
+		while [ ! -d /sys/class/tty/ttyUSB0 ] ; do
+			:
+	done
+	cat /dev/ttyUSB0 >> xdbc.log
+	done
+	===== end of bash scripts ===============
+
+You should be able to see the early boot message in xdbc.log.
+
+If it doesn't work, please ask it on the <linux-usb@vger.kernel.org>
+mailing list. Below USB hosts have been verified to work::
+
+	Intel Corporation Sunrise Point-H USB 3.0 xHCI Controller
+	Intel Corporation Wildcat Point-LP USB xHCI Controller
-- 
2.1.4

^ permalink raw reply related	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-01  4:59 ` [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
@ 2016-11-09  9:23   ` Thomas Gleixner
  2016-11-10  1:13     ` Lu Baolu
  2016-11-09  9:37   ` Thomas Gleixner
  1 sibling, 1 reply; 17+ messages in thread
From: Thomas Gleixner @ 2016-11-09  9:23 UTC (permalink / raw)
  To: Lu Baolu
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

On Tue, 1 Nov 2016, Lu Baolu wrote:
> +static int __init xdbc_init(void)
> +{
...
> +	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;
> +	}
> +
> +	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +	xdbc_trace("early mapped IO address released\n");
> +
> +	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);

This is broken. What prevents that 

     - a printk is in progress on another cpu?

     - a printk happens between the unmap and storing the new base ?

Nothing AFAICT. So this needs to be done in a safe way. And just making it

	oldbase = xdbc.xhci_base;
	base = ioremap(....);
	xdbc.xhci_base = base;
	early_iounmap(oldbase);

does not work either because the compiler can rightfully cache
xdbc.xhci_base in the write related functions. The same issue with
xdbc.xdbc_reg.

Thanks,

	tglx

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-01  4:59 ` [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
  2016-11-09  9:23   ` Thomas Gleixner
@ 2016-11-09  9:37   ` Thomas Gleixner
  2016-11-10  1:20     ` Lu Baolu
  1 sibling, 1 reply; 17+ messages in thread
From: Thomas Gleixner @ 2016-11-09  9:37 UTC (permalink / raw)
  To: Lu Baolu
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

On Tue, 1 Nov 2016, Lu Baolu wrote:
> +static void early_xdbc_write(struct console *con, const char *str, u32 n)
> +{
> +	int chunk, ret;
> +	static char buf[XDBC_MAX_PACKET];
> +	int use_cr = 0;
> +
> +	if (!xdbc.xdbc_reg)
> +		return;
> +	memset(buf, 0, XDBC_MAX_PACKET);

How is that dealing with reentrancy?

early_printk() does not protect against it. Peter has a patch to prevent
concurrent access from different cpus, but it cannot and will never prevent
reentrancy on the same cpu (interrupt, nmi).

Thanks,

	tglx

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-09  9:23   ` Thomas Gleixner
@ 2016-11-10  1:13     ` Lu Baolu
  0 siblings, 0 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-10  1:13 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

Hi,

On 11/09/2016 05:23 PM, Thomas Gleixner wrote:
> On Tue, 1 Nov 2016, Lu Baolu wrote:
>> +static int __init xdbc_init(void)
>> +{
> ...
>> +	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;
>> +	}
>> +
>> +	early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
>> +	xdbc_trace("early mapped IO address released\n");
>> +
>> +	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);
> This is broken. What prevents that 
>
>      - a printk is in progress on another cpu?
>
>      - a printk happens between the unmap and storing the new base ?
>
> Nothing AFAICT. So this needs to be done in a safe way. And just making it
>
> 	oldbase = xdbc.xhci_base;
> 	base = ioremap(....);
> 	xdbc.xhci_base = base;
> 	early_iounmap(oldbase);
>
> does not work either because the compiler can rightfully cache
> xdbc.xhci_base in the write related functions. The same issue with
> xdbc.xdbc_reg.

If there isn't a good solution, I will remove the ioremap code and let
it use the early mapped one.

Best regards,
Lu Baolu

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-09  9:37   ` Thomas Gleixner
@ 2016-11-10  1:20     ` Lu Baolu
  2016-11-10  8:56       ` Thomas Gleixner
  0 siblings, 1 reply; 17+ messages in thread
From: Lu Baolu @ 2016-11-10  1:20 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

Hi,

On 11/09/2016 05:37 PM, Thomas Gleixner wrote:
> On Tue, 1 Nov 2016, Lu Baolu wrote:
>> +static void early_xdbc_write(struct console *con, const char *str, u32 n)
>> +{
>> +	int chunk, ret;
>> +	static char buf[XDBC_MAX_PACKET];
>> +	int use_cr = 0;
>> +
>> +	if (!xdbc.xdbc_reg)
>> +		return;
>> +	memset(buf, 0, XDBC_MAX_PACKET);
> How is that dealing with reentrancy?
>
> early_printk() does not protect against it. Peter has a patch to prevent
> concurrent access from different cpus, but it cannot and will never prevent
> reentrancy on the same cpu (interrupt, nmi).

I can use a spinlock_irq to protect reentrancy of interrupt on the same
cpu. But I have no idea about the nmi one. This seems to be a common
issue for all early printk drivers.

Peter, any idea?

Best regards,
Lu Baolu

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-10  1:20     ` Lu Baolu
@ 2016-11-10  8:56       ` Thomas Gleixner
  2016-11-10 11:44         ` Peter Zijlstra
  2016-11-11  2:24         ` Lu Baolu
  0 siblings, 2 replies; 17+ messages in thread
From: Thomas Gleixner @ 2016-11-10  8:56 UTC (permalink / raw)
  To: Lu Baolu
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

On Thu, 10 Nov 2016, Lu Baolu wrote:
> On 11/09/2016 05:37 PM, Thomas Gleixner wrote:
> > On Tue, 1 Nov 2016, Lu Baolu wrote:
> >> +static void early_xdbc_write(struct console *con, const char *str, u32 n)
> >> +{
> >> +	int chunk, ret;
> >> +	static char buf[XDBC_MAX_PACKET];
> >> +	int use_cr = 0;
> >> +
> >> +	if (!xdbc.xdbc_reg)
> >> +		return;
> >> +	memset(buf, 0, XDBC_MAX_PACKET);
> > How is that dealing with reentrancy?
> >
> > early_printk() does not protect against it. Peter has a patch to prevent
> > concurrent access from different cpus, but it cannot and will never prevent
> > reentrancy on the same cpu (interrupt, nmi).
> 
> I can use a spinlock_irq to protect reentrancy of interrupt on the same
> cpu. But I have no idea about the nmi one.

spinlock wont work due to NMIs.

> This seems to be a common issue for all early printk drivers.

No. The other early printk drivers like serial do not have that problem as
they simply do:

   while (*buf) {
      while (inb(UART) & TX_BUSY)
   	 cpu_relax();
      outb(*buf++, UART);
   }

The wait for the UART to become ready is independent of the context as it
solely depends on the hardware.

As a result you can see the output from irq/nmi intermingled with the one
from thread context, but that's the only problem they have.

The only thing you can do to make this work is to prevent printing in NMI
context:

write()
{
	if (in_nmi())
		return;
	
	raw_spinlock_irqsave(&lock, flags);
	....

That fully serializes the writes and just ignores NMI context printks. Not
optimal, but I fear that's all you can do.

Thanks,

	tglx

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-10  8:56       ` Thomas Gleixner
@ 2016-11-10 11:44         ` Peter Zijlstra
  2016-11-11  4:33           ` Lu Baolu
  2016-11-11  2:24         ` Lu Baolu
  1 sibling, 1 reply; 17+ messages in thread
From: Peter Zijlstra @ 2016-11-10 11:44 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: Lu Baolu, Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar,
	linux-usb, x86, LKML

On Thu, Nov 10, 2016 at 09:56:41AM +0100, Thomas Gleixner wrote:
> On Thu, 10 Nov 2016, Lu Baolu wrote:

> > This seems to be a common issue for all early printk drivers.
> 
> No. The other early printk drivers like serial do not have that problem as
> they simply do:
> 
>    while (*buf) {
>       while (inb(UART) & TX_BUSY)
>    	 cpu_relax();
>       outb(*buf++, UART);
>    }

Right, which is why actual UARTs rule. If only laptops still had pinouts
for them life would be sooooo much better.

Ideally the USB debug port would be a virtual UART and its interface as
simple and robust.

> The wait for the UART to become ready is independent of the context as it
> solely depends on the hardware.
> 
> As a result you can see the output from irq/nmi intermingled with the one
> from thread context, but that's the only problem they have.
> 
> The only thing you can do to make this work is to prevent printing in NMI
> context:
> 
> write()
> {
> 	if (in_nmi())
> 		return;
> 	
> 	raw_spinlock_irqsave(&lock, flags);
> 	....
> 
> That fully serializes the writes and just ignores NMI context printks. Not
> optimal, but I fear that's all you can do.

I would also suggest telling the hardware people they have designed
something near the brink of useless. If you cannot do random exception
context debugging (#DB, #NMI, #MCE etc..) then there's a whole host of
problems that simply cannot be debugged.

Also note that kdb runs from NMI context, so you'll not be able to
support that either.

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-10  8:56       ` Thomas Gleixner
  2016-11-10 11:44         ` Peter Zijlstra
@ 2016-11-11  2:24         ` Lu Baolu
  2016-11-11  2:49           ` Lu Baolu
  1 sibling, 1 reply; 17+ messages in thread
From: Lu Baolu @ 2016-11-11  2:24 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

Hi,

On 11/10/2016 04:56 PM, Thomas Gleixner wrote:
> On Thu, 10 Nov 2016, Lu Baolu wrote:
>> On 11/09/2016 05:37 PM, Thomas Gleixner wrote:
>>> On Tue, 1 Nov 2016, Lu Baolu wrote:
>>>> +static void early_xdbc_write(struct console *con, const char *str, u32 n)
>>>> +{
>>>> +	int chunk, ret;
>>>> +	static char buf[XDBC_MAX_PACKET];
>>>> +	int use_cr = 0;
>>>> +
>>>> +	if (!xdbc.xdbc_reg)
>>>> +		return;
>>>> +	memset(buf, 0, XDBC_MAX_PACKET);
>>> How is that dealing with reentrancy?
>>>
>>> early_printk() does not protect against it. Peter has a patch to prevent
>>> concurrent access from different cpus, but it cannot and will never prevent
>>> reentrancy on the same cpu (interrupt, nmi).
>> I can use a spinlock_irq to protect reentrancy of interrupt on the same
>> cpu. But I have no idea about the nmi one.
> spinlock wont work due to NMIs.

Yes, of course.

>
>> This seems to be a common issue for all early printk drivers.
> No. The other early printk drivers like serial do not have that problem as
> they simply do:
>
>    while (*buf) {
>       while (inb(UART) & TX_BUSY)
>    	 cpu_relax();
>       outb(*buf++, UART);
>    }
>
> The wait for the UART to become ready is independent of the context as it
> solely depends on the hardware.
>
> As a result you can see the output from irq/nmi intermingled with the one
> from thread context, but that's the only problem they have.

Yes, you are right.

>
> The only thing you can do to make this work is to prevent printing in NMI
> context:
>
> write()
> {
> 	if (in_nmi())
> 		return;
> 	
> 	raw_spinlock_irqsave(&lock, flags);
> 	....
>
> That fully serializes the writes and just ignores NMI context printks. Not
> optimal, but I fear that's all you can do.

Yes. But I want to add a bit more.

write()
{
	if (in_nmi() && raw_spin_is_locked(&lock)) {
		trace("... ...");
		return;
	}

	raw_spinlock_irqsave(&lock, flags);
	....


Best regards,
Lu Baolu

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-11  2:24         ` Lu Baolu
@ 2016-11-11  2:49           ` Lu Baolu
  0 siblings, 0 replies; 17+ messages in thread
From: Lu Baolu @ 2016-11-11  2:49 UTC (permalink / raw)
  To: Thomas Gleixner
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86,
	LKML, Peter Zijlstra

Hi,

On 11/11/2016 10:24 AM, Lu Baolu wrote:
>> The only thing you can do to make this work is to prevent printing in NMI
>> > context:
>> >
>> > write()
>> > {
>> > 	if (in_nmi())
>> > 		return;
>> > 	
>> > 	raw_spinlock_irqsave(&lock, flags);
>> > 	....
>> >
>> > That fully serializes the writes and just ignores NMI context printks. Not
>> > optimal, but I fear that's all you can do.
> Yes. But I want to add a bit more.
>
> write()
> {
> 	if (in_nmi() && raw_spin_is_locked(&lock)) {
> 		trace("... ...");
> 		return;
> 	}
>
> 	raw_spinlock_irqsave(&lock, flags);
> 	....

Or...?

write()
{
	if (in_nmi() && raw_spin_is_locked(&lock)) {
		save_nmi_message_in_local_buf();
		set_nmi_message_pending_flag();
		return;
	}

	if (nmi_message_pending_flag_is_set()) {
		write_nmi_message();
		clear_nmi_message_pending_flag();
	}

	raw_spinlock_irqsave(&lock, flags);
	....


Best regards,
Lu Baolu

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-10 11:44         ` Peter Zijlstra
@ 2016-11-11  4:33           ` Lu Baolu
  2016-11-11 12:28             ` Peter Zijlstra
  0 siblings, 1 reply; 17+ messages in thread
From: Lu Baolu @ 2016-11-11  4:33 UTC (permalink / raw)
  To: Peter Zijlstra, Thomas Gleixner
  Cc: Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar, linux-usb, x86, LKML

Hi Peter,

On 11/10/2016 07:44 PM, Peter Zijlstra wrote:
> On Thu, Nov 10, 2016 at 09:56:41AM +0100, Thomas Gleixner wrote:
>> On Thu, 10 Nov 2016, Lu Baolu wrote:
>>> This seems to be a common issue for all early printk drivers.
>> No. The other early printk drivers like serial do not have that problem as
>> they simply do:
>>
>>    while (*buf) {
>>       while (inb(UART) & TX_BUSY)
>>    	 cpu_relax();
>>       outb(*buf++, UART);
>>    }
> Right, which is why actual UARTs rule. If only laptops still had pinouts
> for them life would be sooooo much better.
>
> Ideally the USB debug port would be a virtual UART and its interface as
> simple and robust.
>
>> The wait for the UART to become ready is independent of the context as it
>> solely depends on the hardware.
>>
>> As a result you can see the output from irq/nmi intermingled with the one
>> from thread context, but that's the only problem they have.
>>
>> The only thing you can do to make this work is to prevent printing in NMI
>> context:
>>
>> write()
>> {
>> 	if (in_nmi())
>> 		return;
>> 	
>> 	raw_spinlock_irqsave(&lock, flags);
>> 	....
>>
>> That fully serializes the writes and just ignores NMI context printks. Not
>> optimal, but I fear that's all you can do.
> I would also suggest telling the hardware people they have designed
> something near the brink of useless. If you cannot do random exception
> context debugging (#DB, #NMI, #MCE etc..) then there's a whole host of
> problems that simply cannot be debugged.
>
> Also note that kdb runs from NMI context, so you'll not be able to
> support that either.
>

Things become complicated when it comes to USB debug port.
But it's still addressable.

At this time, we can do it like this.

write()
{
	if (in_nmi() && raw_spin_is_locked(&lock))
		return;

	raw_spinlock_irqsave(&lock, flags);
	....


This will filter some messages from NMI handler in case that
another thread is holding the spinlock. I have no idea about
how much chance could a debug user faces this. But it might
further be fixed with below enhancement.

write()
{
	if (in_nmi() && raw_spin_is_locked(&lock)) {
		produce_a_pending_item_in_ring();
		return;
	}

	raw_spinlock_irqsave(&lock, flags);

	while (!pending_item_ring_is_empty)
		consume_a_pending_item_in_ring();

	....


We can design the pending item ring in a producer-consumer
model. It's easy to avoid race between the producer and
consumer.

Best regards,
Lu Baolu

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-11  4:33           ` Lu Baolu
@ 2016-11-11 12:28             ` Peter Zijlstra
  2016-11-12  7:35               ` Lu Baolu
  0 siblings, 1 reply; 17+ messages in thread
From: Peter Zijlstra @ 2016-11-11 12:28 UTC (permalink / raw)
  To: Lu Baolu
  Cc: Thomas Gleixner, Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar,
	linux-usb, x86, LKML

On Fri, Nov 11, 2016 at 12:33:29PM +0800, Lu Baolu wrote:

> Things become complicated when it comes to USB debug port.
> But it's still addressable.
> 
> At this time, we can do it like this.
> 
> write()
> {
> 	if (in_nmi() && raw_spin_is_locked(&lock))
> 		return;
> 
> 	raw_spinlock_irqsave(&lock, flags);
> 	....
> 

Please use raw_spin_trlock_irqsave() instead, spin_is_locked() is fairly
icky.

Also, there's a bunch of exception contexts that do not set in_nmi().
That is in_nmi() is really only set for #NM. #MC and #DB and
others do not set this.

> This will filter some messages from NMI handler in case that
> another thread is holding the spinlock. I have no idea about
> how much chance could a debug user faces this. But it might
> further be fixed with below enhancement.
> 
> write()
> {
> 	if (in_nmi() && raw_spin_is_locked(&lock)) {
> 		produce_a_pending_item_in_ring();
> 		return;
> 	}
> 
> 	raw_spinlock_irqsave(&lock, flags);
> 
> 	while (!pending_item_ring_is_empty)
> 		consume_a_pending_item_in_ring();
> 
> 	....
> 
> 
> We can design the pending item ring in a producer-consumer
> model. It's easy to avoid race between the producer and
> consumer.

Problem is that the consumer might never happen, those are the fun most
bugs.

Not being able to deal with random nested exception context really
reduces the utility of this thing.

Again, a UART rules. Make a virtual UART in hardware, that'd be totally
awesome. This thing, I'm not convinced its worth having.

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-11 12:28             ` Peter Zijlstra
@ 2016-11-12  7:35               ` Lu Baolu
  2016-11-12 11:32                 ` Thomas Gleixner
  0 siblings, 1 reply; 17+ messages in thread
From: Lu Baolu @ 2016-11-12  7:35 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Thomas Gleixner, Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar,
	linux-usb, x86, LKML

Hi Peter,

On 11/11/2016 08:28 PM, Peter Zijlstra wrote:
> On Fri, Nov 11, 2016 at 12:33:29PM +0800, Lu Baolu wrote:
>
>> Things become complicated when it comes to USB debug port.
>> But it's still addressable.
>>
>> At this time, we can do it like this.
>>
>> write()
>> {
>> 	if (in_nmi() && raw_spin_is_locked(&lock))
>> 		return;
>>
>> 	raw_spinlock_irqsave(&lock, flags);
>> 	....
>>
> Please use raw_spin_trlock_irqsave() instead, spin_is_locked() is fairly
> icky.

Sure.

>
> Also, there's a bunch of exception contexts that do not set in_nmi().
> That is in_nmi() is really only set for #NM. #MC and #DB and
> others do not set this.

That's worth another fix patch. Let me look into it later.

>
>> This will filter some messages from NMI handler in case that
>> another thread is holding the spinlock. I have no idea about
>> how much chance could a debug user faces this. But it might
>> further be fixed with below enhancement.
>>
>> write()
>> {
>> 	if (in_nmi() && raw_spin_is_locked(&lock)) {
>> 		produce_a_pending_item_in_ring();
>> 		return;
>> 	}
>>
>> 	raw_spinlock_irqsave(&lock, flags);
>>
>> 	while (!pending_item_ring_is_empty)
>> 		consume_a_pending_item_in_ring();
>>
>> 	....
>>
>>
>> We can design the pending item ring in a producer-consumer
>> model. It's easy to avoid race between the producer and
>> consumer.
> Problem is that the consumer might never happen, those are the fun most
> bugs.
>
> Not being able to deal with random nested exception context really
> reduces the utility of this thing.
>
> Again, a UART rules. Make a virtual UART in hardware, that'd be totally
> awesome. This thing, I'm not convinced its worth having.

This is the initial work. It helps at least in cases where people need
to dump kernel messages but lacking of a console. It's also a cheap
way, people don't need to buy any third-party devices.

With more and more people trying and enhancing it, it will become
more robust and helpful.

Best regards,
Lu Baolu

^ permalink raw reply	[flat|nested] 17+ messages in thread

* Re: [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability
  2016-11-12  7:35               ` Lu Baolu
@ 2016-11-12 11:32                 ` Thomas Gleixner
  0 siblings, 0 replies; 17+ messages in thread
From: Thomas Gleixner @ 2016-11-12 11:32 UTC (permalink / raw)
  To: Lu Baolu
  Cc: Peter Zijlstra, Greg Kroah-Hartman, Mathias Nyman, Ingo Molnar,
	linux-usb, x86, LKML

On Sat, 12 Nov 2016, Lu Baolu wrote:
> On 11/11/2016 08:28 PM, Peter Zijlstra wrote:
> > Again, a UART rules. Make a virtual UART in hardware, that'd be totally
> > awesome. This thing, I'm not convinced its worth having.
> 
> This is the initial work. It helps at least in cases where people need
> to dump kernel messages but lacking of a console. It's also a cheap
> way, people don't need to buy any third-party devices.
> 
> With more and more people trying and enhancing it, it will become
> more robust and helpful.

Well, not really. The hardware does not allow you what an UART allows you
to do and never will, no matter how many people are trying to enhance the
software part of it.

Thanks,

	tglx

^ permalink raw reply	[flat|nested] 17+ messages in thread

end of thread, other threads:[~2016-11-12 11:35 UTC | newest]

Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-11-01  4:59 [PATCH v4 0/4] usb: early: add support for early printk through USB3 debug port Lu Baolu
2016-11-01  4:59 ` [PATCH v4 1/4] usb: dbc: early driver for xhci debug capability Lu Baolu
2016-11-09  9:23   ` Thomas Gleixner
2016-11-10  1:13     ` Lu Baolu
2016-11-09  9:37   ` Thomas Gleixner
2016-11-10  1:20     ` Lu Baolu
2016-11-10  8:56       ` Thomas Gleixner
2016-11-10 11:44         ` Peter Zijlstra
2016-11-11  4:33           ` Lu Baolu
2016-11-11 12:28             ` Peter Zijlstra
2016-11-12  7:35               ` Lu Baolu
2016-11-12 11:32                 ` Thomas Gleixner
2016-11-11  2:24         ` Lu Baolu
2016-11-11  2:49           ` Lu Baolu
2016-11-01  4:59 ` [PATCH v4 2/4] x86: add support for earlyprintk via USB3 debug port Lu Baolu
2016-11-01  4:59 ` [PATCH v4 3/4] usb: serial: usb_debug: add support for dbc debug device Lu Baolu
2016-11-01  4:59 ` [PATCH v4 4/4] usb: doc: add document for USB3 debug port usage Lu Baolu

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