xHCI compatible USB host controllers(i.e. super-speed USB3 controllers)
can be implemented with the Debug Capability(DbC). It presents a debug
device which is fully compliant with the USB framework and provides the
equivalent of a very high performance full-duplex serial link. The debug
capability operation model and registers interface are defined in 7.6.8
of the xHCI specification, revision 1.1.

The DbC debug device shares a root port with the xHCI host. By default,
the debug capability is disabled and the root port is assigned to xHCI.
When the DbC is enabled, the root port will be assigned to the DbC debug
device, and the xHCI sees nothing on this port. This implementation uses
a sysfs node named <dbc> under the xHCI device to manage the enabling
and disabling of the debug capability.

When the debug capability is enabled, it will present a debug device
through the debug port. This debug device is fully compliant with the
USB3 framework, and it can be enumerated by a debug host on the other
end of the USB link. As soon as the debug device is configured, a TTY
serial device named /dev/ttyGSn will be created.

One use of this link is running a login service on the debug target.
Hence it can be remote accessed by a debug host. Another use case can
probably be found in servers. It provides a peer-to-peer USB link
between two host-only machines. This provides a reasonable out-of-band
communication method between two servers.

Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
---
 .../ABI/testing/sysfs-bus-pci-drivers-xhci_hcd     |   25 +
 drivers/usb/host/Kconfig                           |    9 +
 drivers/usb/host/Makefile                          |    5 +
 drivers/usb/host/xhci-dbgcap.c                     | 1100 ++++++++++++++++++++
 drivers/usb/host/xhci-dbgcap.h                     |  194 ++++
 drivers/usb/host/xhci-trace.h                      |   65 ++
 drivers/usb/host/xhci.c                            |   10 +
 drivers/usb/host/xhci.h                            |    1 +
 include/linux/usb/gadget.h                         |   52 +
 9 files changed, 1461 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
 create mode 100644 drivers/usb/host/xhci-dbgcap.c
 create mode 100644 drivers/usb/host/xhci-dbgcap.h

diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd 
b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
new file mode 100644
index 0000000..0088aba
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
@@ -0,0 +1,25 @@
+What:          /sys/bus/pci/drivers/xhci_hcd/.../dbc
+Date:          June 2017
+Contact:       Lu Baolu <baolu...@linux.intel.com>
+Description:
+               xHCI compatible USB host controllers (i.e. super-speed
+               USB3 controllers) are often implemented with the Debug
+               Capability (DbC). It can present a debug device which
+               is fully compliant with the USB framework and provides
+               the equivalent of a very high performance full-duplex
+               serial link for debug purpose.
+
+               The DbC debug device shares a root port with xHCI host.
+               When the DbC is enabled, the root port will be assigned
+               to the Debug Capability. Otherwise, it will be assigned
+               to xHCI.
+
+               Writing "enable" to this attribute will enable the DbC
+               functionality and the shared root port will be assigned
+               to the DbC device. Writing "disable" to this attribute
+               will disable the DbC functionality and the shared root
+               port will roll back to the xHCI.
+
+               Reading this attribute gives the state of the DbC. It
+               can be one of the following states: disabled, enabled,
+               initialized, connected, configured and stalled.
diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index fa5692d..968a196 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig
@@ -27,6 +27,15 @@ config USB_XHCI_HCD
          module will be called xhci-hcd.
 
 if USB_XHCI_HCD
+config USB_XHCI_DBGCAP
+       bool "xHCI support for debug capability"
+       depends on TTY
+       select USB_U_SERIAL
+       ---help---
+         Say 'Y' to enable the support for the xHCI debug capability. Make
+         sure that your xHCI host supports the extended debug capability and
+         you want a TTY serial device based on the xHCI debug capability
+         before enabling this option. If unsure, say 'N'.
 
 config USB_XHCI_PCI
        tristate
diff --git a/drivers/usb/host/Makefile b/drivers/usb/host/Makefile
index cf2691f..4629d20 100644
--- a/drivers/usb/host/Makefile
+++ b/drivers/usb/host/Makefile
@@ -13,6 +13,11 @@ fhci-$(CONFIG_FHCI_DEBUG) += fhci-dbg.o
 xhci-hcd-y := xhci.o xhci-mem.o
 xhci-hcd-y += xhci-ring.o xhci-hub.o xhci-dbg.o
 xhci-hcd-y += xhci-trace.o
+
+ifneq ($(CONFIG_USB_XHCI_DBGCAP), )
+       xhci-hcd-y += xhci-dbgcap.o
+endif
+
 ifneq ($(CONFIG_USB_XHCI_MTK), )
        xhci-hcd-y += xhci-mtk-sch.o
 endif
diff --git a/drivers/usb/host/xhci-dbgcap.c b/drivers/usb/host/xhci-dbgcap.c
new file mode 100644
index 0000000..6e5b505
--- /dev/null
+++ b/drivers/usb/host/xhci-dbgcap.c
@@ -0,0 +1,1100 @@
+/**
+ * xhci-dbgcap.c - xHCI debug capability support
+ *
+ * Copyright (C) 2017 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu...@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.
+ */
+#include <linux/dma-mapping.h>
+#include <linux/slab.h>
+
+#include "xhci.h"
+#include "xhci-trace.h"
+#include "xhci-dbgcap.h"
+
+static inline void *
+dbc_dma_alloc_coherent(struct xhci_hcd *xhci, size_t size,
+                      dma_addr_t *dma_handle, gfp_t flags)
+{
+       void            *vaddr;
+
+       vaddr = dma_alloc_coherent(xhci_to_hcd(xhci)->self.sysdev,
+                                  size, dma_handle, flags);
+       memset(vaddr, 0, size);
+       return vaddr;
+}
+
+static inline void
+dbc_dma_free_coherent(struct xhci_hcd *xhci, size_t size,
+                     void *cpu_addr, dma_addr_t dma_handle)
+{
+       if (cpu_addr)
+               dma_free_coherent(xhci_to_hcd(xhci)->self.sysdev,
+                                 size, cpu_addr, dma_handle);
+}
+
+static inline void xhci_put_utf16(u16 *s, const char *c)
+{
+       int             i;
+       size_t          size;
+
+       size = strlen(c);
+       for (i = 0; i < size; i++)
+               s[i] = cpu_to_le16(c[i]);
+}
+
+static u32 xhci_dbc_populate_strings(struct dbc_strings *strings)
+{
+       struct usb_string_descriptor    *s_desc;
+       u32                             string_length;
+
+       /* Serial string: */
+       s_desc = (struct usb_string_descriptor *)strings->serial;
+       xhci_put_utf16(s_desc->wData, DBC_STRING_SERIAL);
+
+       s_desc->bLength         = (strlen(DBC_STRING_SERIAL) + 1) * 2;
+       s_desc->bDescriptorType = USB_DT_STRING;
+       string_length           = s_desc->bLength;
+       string_length           <<= 8;
+
+       /* Product string: */
+       s_desc = (struct usb_string_descriptor *)strings->product;
+       xhci_put_utf16(s_desc->wData, DBC_STRING_PRODUCT);
+
+       s_desc->bLength         = (strlen(DBC_STRING_PRODUCT) + 1) * 2;
+       s_desc->bDescriptorType = USB_DT_STRING;
+       string_length           += s_desc->bLength;
+       string_length           <<= 8;
+
+       /* Manufacture string: */
+       s_desc = (struct usb_string_descriptor *)strings->manufacturer;
+       xhci_put_utf16(s_desc->wData, DBC_STRING_MANUFACTURER);
+
+       s_desc->bLength         = (strlen(DBC_STRING_MANUFACTURER) + 1) * 2;
+       s_desc->bDescriptorType = USB_DT_STRING;
+       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;
+
+       return string_length;
+}
+
+static void xhci_dbc_populate_contexts(struct xhci_hcd *xhci, u32 
string_length)
+{
+       struct xhci_dbc         *dbc;
+       struct dbc_info_context *info;
+       struct xhci_ep_ctx      *ep_ctx;
+       u32                     dev_info;
+       dma_addr_t              deq, dma;
+       unsigned int            max_burst;
+
+       dbc = xhci->dbc;
+       if (!dbc)
+               return;
+
+       /* Populate info Context: */
+       info                    = (struct dbc_info_context *)dbc->ctx->bytes;
+       dma                     = dbc->string_dma;
+       info->string0           = cpu_to_le64(dma);
+       info->manufacturer      = cpu_to_le64(dma + DBC_MAX_STRING_LENGTH);
+       info->product           = cpu_to_le64(dma + DBC_MAX_STRING_LENGTH * 2);
+       info->serial            = cpu_to_le64(dma + DBC_MAX_STRING_LENGTH * 3);
+       info->length            = cpu_to_le32(string_length);
+
+       /* Populate bulk out endpoint context: */
+       ep_ctx                  = dbc_bulkout_ctx(dbc);
+       max_burst               = DBC_CTRL_MAXBURST(readl(&dbc->regs->control));
+       deq                     = dbc_bulkout_enq(dbc);
+       ep_ctx->ep_info         = 0;
+       ep_ctx->ep_info2        = dbc_epctx_info2(BULK_OUT_EP, 1024, max_burst);
+       ep_ctx->deq             = cpu_to_le64(deq | dbc->ring_out->cycle_state);
+
+       /* Populate bulk in endpoint context: */
+       ep_ctx                  = dbc_bulkin_ctx(dbc);
+       deq                     = dbc_bulkin_enq(dbc);
+       ep_ctx->ep_info         = 0;
+       ep_ctx->ep_info2        = dbc_epctx_info2(BULK_IN_EP, 1024, max_burst);
+       ep_ctx->deq             = cpu_to_le64(deq | dbc->ring_in->cycle_state);
+
+       /* Set DbC context and info registers: */
+       xhci_write_64(xhci, dbc->ctx->dma, &dbc->regs->dccp);
+
+       dev_info = cpu_to_le32((DBC_VENDOR_ID << 16) | DBC_PROTOCOL);
+       writel(dev_info, &dbc->regs->devinfo1);
+
+       dev_info = cpu_to_le32((DBC_DEVICE_REV << 16) | DBC_PRODUCT_ID);
+       writel(dev_info, &dbc->regs->devinfo2);
+}
+
+static void xhci_dbc_giveback(struct dbc_request *dreq, int status)
+       __releases(&dbc->lock)
+       __acquires(&dbc->lock)
+{
+       struct dbc_ep           *dep = dreq->dep;
+       struct usb_request      *req = &dreq->request;
+       struct xhci_dbc         *dbc = dep->dbc;
+       struct device           *dev = xhci_to_hcd(dbc->xhci)->self.sysdev;
+
+       list_del_init(&dreq->list);
+       dreq->trb_dma = 0;
+       dreq->trb = NULL;
+
+       if (req->status == -EINPROGRESS)
+               req->status = status;
+
+       dma_unmap_single(dev,
+                        req->dma,
+                        req->length,
+                        dbc_ep_dma_direction(dep));
+
+       /* Give back the transfer request: */
+       trace_xhci_dbc_giveback_request(dreq);
+       spin_unlock(&dbc->lock);
+       req->complete(&dep->ep, req);
+       spin_lock(&dbc->lock);
+}
+
+static void xhci_dbc_flush_single_request(struct dbc_request *dreq)
+{
+       union xhci_trb  *trb = dreq->trb;
+
+       trb->generic.field[0]   = 0;
+       trb->generic.field[1]   = 0;
+       trb->generic.field[2]   = 0;
+       trb->generic.field[3]   &= cpu_to_le32(TRB_CYCLE);
+       trb->generic.field[3]   |= cpu_to_le32(TRB_TYPE(TRB_TR_NOOP));
+
+       xhci_dbc_giveback(dreq, -ECONNRESET);
+}
+
+static void xhci_dbc_flush_endpoint_requests(struct dbc_ep *dep)
+{
+       struct dbc_request      *dreq, *tmp;
+
+       list_for_each_entry_safe(dreq, tmp, &dep->pending_list, list)
+               xhci_dbc_flush_single_request(dreq);
+}
+
+static void xhci_dbc_flush_reqests(struct xhci_dbc *dbc)
+{
+       int                     i;
+       struct dbc_ep           *dep;
+
+       for (i = BULK_OUT; i <= BULK_IN; i++) {
+               dep = dbc->eps[i];
+               xhci_dbc_flush_endpoint_requests(dep);
+       }
+}
+
+static int dbc_gadget_ep_enable(struct usb_ep *ep,
+                               const struct usb_endpoint_descriptor *desc)
+{
+       struct dbc_ep           *dep = ep_to_dep(ep);
+       struct xhci_dbc         *dbc = dep->dbc;
+
+       return !(dbc->state == DS_CONFIGURED);
+}
+
+static int dbc_gadget_ep_disable(struct usb_ep *ep)
+{
+       struct dbc_ep           *dep = ep_to_dep(ep);
+       struct xhci_dbc         *dbc = dep->dbc;
+
+       spin_lock(&dbc->lock);
+       xhci_dbc_flush_reqests(dbc);
+       spin_unlock(&dbc->lock);
+
+       return 0;
+}
+
+static struct usb_request *
+dbc_gadget_ep_alloc_request(struct usb_ep *ep, gfp_t gfp_flags)
+{
+       struct dbc_request      *dreq;
+       struct dbc_ep           *dep = ep_to_dep(ep);
+
+       dreq = kzalloc(sizeof(*dreq), gfp_flags);
+       if (!dreq)
+               return NULL;
+
+       dreq->dep = dep;
+       INIT_LIST_HEAD(&dreq->list);
+
+       trace_xhci_dbc_alloc_request(dreq);
+
+       return &dreq->request;
+}
+
+static void
+dbc_gadget_ep_free_request(struct usb_ep *ep, struct usb_request *request)
+{
+       struct dbc_request      *dreq = req_to_dreq(request);
+
+       trace_xhci_dbc_free_request(dreq);
+
+       kfree(dreq);
+}
+
+static void
+xhci_dbc_queue_trb(struct xhci_ring *ring, u32 field1,
+                  u32 field2, u32 field3, u32 field4)
+{
+       union xhci_trb          *trb, *next;
+
+       trb = ring->enqueue;
+       trb->generic.field[0]   = cpu_to_le32(field1);
+       trb->generic.field[1]   = cpu_to_le32(field2);
+       trb->generic.field[2]   = cpu_to_le32(field3);
+       trb->generic.field[3]   = cpu_to_le32(field4);
+
+       trace_xhci_dbc_gadget_ep_queue(ring, &trb->generic);
+
+       ring->num_trbs_free--;
+       next = ++(ring->enqueue);
+       if (TRB_TYPE_LINK_LE32(next->link.control)) {
+               next->link.control ^= cpu_to_le32(TRB_CYCLE);
+               ring->enqueue = ring->enq_seg->trbs;
+               ring->cycle_state ^= 1;
+       }
+}
+
+static int xhci_dbc_queue_bulk_tx(struct dbc_ep *dep,
+                                 struct dbc_request *dreq)
+{
+       u64                     addr;
+       union xhci_trb          *trb;
+       unsigned int            num_trbs;
+       struct xhci_dbc         *dbc = dep->dbc;
+       struct xhci_ring        *ring = dep->ring;
+       struct usb_request      *req = &dreq->request;
+       u32                     length, control, cycle;
+
+       num_trbs = count_trbs(req->dma, req->length);
+       WARN_ON(num_trbs != 1);
+       if (ring->num_trbs_free < num_trbs)
+               return -EBUSY;
+
+       addr    = req->dma;
+       trb     = ring->enqueue;
+       cycle   = ring->cycle_state;
+       length  = TRB_LEN(req->length);
+       control = TRB_TYPE(TRB_NORMAL) | TRB_IOC;
+
+       if (cycle)
+               control &= cpu_to_le32(~TRB_CYCLE);
+       else
+               control |= cpu_to_le32(TRB_CYCLE);
+
+       dreq->trb = ring->enqueue;
+       dreq->trb_dma = xhci_trb_virt_to_dma(ring->enq_seg, ring->enqueue);
+       xhci_dbc_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->generic.field[3] |= cpu_to_le32(TRB_CYCLE);
+       else
+               trb->generic.field[3] &= cpu_to_le32(~TRB_CYCLE);
+
+       writel(DBC_DOOR_BELL_TARGET(dep->direction), &dbc->regs->doorbell);
+
+       return 0;
+}
+
+static int
+__dbc_gadget_ep_queue(struct dbc_ep *dep, struct dbc_request *dreq)
+{
+       int                     ret;
+       struct device           *dev;
+       struct xhci_dbc         *dbc = dep->dbc;
+       struct xhci_hcd         *xhci = dbc->xhci;
+       struct usb_request      *req = &dreq->request;
+
+       dev = xhci_to_hcd(xhci)->self.sysdev;
+
+       req->actual             = 0;
+       req->status             = -EINPROGRESS;
+
+       if (!req->length || !req->buf)
+               return -EINVAL;
+
+       req->dma = dma_map_single(dev,
+                                 req->buf,
+                                 req->length,
+                                 dbc_ep_dma_direction(dep));
+       if (dma_mapping_error(dev, req->dma)) {
+               xhci_err(xhci, "failed to map buffer\n");
+               return -EFAULT;
+       }
+
+       ret = xhci_dbc_queue_bulk_tx(dep, dreq);
+       if (ret) {
+               xhci_err(xhci, "failed to queue trbs\n");
+               dma_unmap_single(dev,
+                                req->dma,
+                                req->length,
+                                dbc_ep_dma_direction(dep));
+               return -EFAULT;
+       }
+
+       list_add_tail(&dreq->list, &dep->pending_list);
+
+       return 0;
+}
+
+static int dbc_gadget_ep_queue(struct usb_ep *ep,
+                              struct usb_request *request,
+                              gfp_t gfp_flags)
+{
+       struct dbc_request      *dreq = req_to_dreq(request);
+       struct dbc_ep           *dep = ep_to_dep(ep);
+       struct xhci_dbc         *dbc = dep->dbc;
+       int                     ret = -ECONNRESET;
+
+       spin_lock(&dbc->lock);
+       if (dbc->state == DS_CONFIGURED) {
+               ret = __dbc_gadget_ep_queue(dep, dreq);
+               trace_xhci_dbc_queue_request(dreq);
+       }
+       spin_unlock(&dbc->lock);
+
+       return ret;
+}
+
+static const struct usb_ep_ops xhci_dbc_gadget_ep_ops = {
+       .enable         = dbc_gadget_ep_enable,
+       .disable        = dbc_gadget_ep_disable,
+       .alloc_request  = dbc_gadget_ep_alloc_request,
+       .free_request   = dbc_gadget_ep_free_request,
+       .queue          = dbc_gadget_ep_queue,
+};
+
+static inline struct dbc_ep *
+xhci_dbc_alloc_endpoint(struct xhci_hcd *xhci, bool direction, gfp_t flags)
+{
+       struct usb_ep           *ep;
+       struct dbc_ep           *dep;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       dep = kzalloc(sizeof(*dep), flags);
+       if (!dep)
+               return NULL;
+
+       ep                      = &dep->ep;
+       ep->name                = direction ? "ep-dbc-in" : "ep-dbc-out";
+       ep->ops                 = &xhci_dbc_gadget_ep_ops;
+       ep->caps.type_bulk      = 1;
+       ep->caps.dir_in         = !direction;
+       ep->caps.dir_out        = direction;
+       ep->maxpacket           = DBC_MAX_PACKET;
+       ep->maxpacket_limit     = DBC_MAX_PACKET;
+       ep->maxburst            = DBC_CTRL_MAXBURST(readl(&dbc->regs->control));
+       dep->dbc                = dbc;
+       dep->direction          = direction;
+       dep->ring               = direction ? dbc->ring_in : dbc->ring_out;
+
+       INIT_LIST_HEAD(&dep->pending_list);
+
+       return dep;
+}
+
+static int xhci_dbc_gadget_eps_init(struct xhci_hcd *xhci, gfp_t flags)
+{
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       dbc->eps[BULK_OUT] = xhci_dbc_alloc_endpoint(xhci, BULK_OUT, flags);
+       dbc->eps[BULK_IN] = xhci_dbc_alloc_endpoint(xhci, BULK_IN, flags);
+
+       if (!dbc->eps[BULK_OUT] || !dbc->eps[BULK_IN]) {
+               kfree(dbc->eps[BULK_OUT]);
+               kfree(dbc->eps[BULK_IN]);
+
+               return -ENOMEM;
+       }
+
+       dbc->gs_port.in = &dbc->eps[BULK_OUT]->ep;
+       dbc->gs_port.out = &dbc->eps[BULK_IN]->ep;
+
+       return 0;
+}
+
+static void xhci_dbc_gadget_eps_exit(struct xhci_hcd *xhci)
+{
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       kfree(dbc->gs_port.in);
+       kfree(dbc->gs_port.out);
+}
+
+static int xhci_dbc_mem_init(struct xhci_hcd *xhci, gfp_t flags)
+{
+       int                     ret;
+       dma_addr_t              deq;
+       u32                     string_length;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       /* Allocate various rings for events and transfers: */
+       dbc->ring_evt = xhci_ring_alloc(xhci, 1, 1, TYPE_EVENT, 0, flags);
+       if (!dbc->ring_evt)
+               goto evt_fail;
+
+       dbc->ring_in = xhci_ring_alloc(xhci, 1, 1, TYPE_BULK, 0, flags);
+       if (!dbc->ring_in)
+               goto in_fail;
+
+       dbc->ring_out = xhci_ring_alloc(xhci, 1, 1, TYPE_BULK, 0, flags);
+       if (!dbc->ring_out)
+               goto out_fail;
+
+       /* Allocate and populate ERST: */
+       ret = xhci_alloc_erst(xhci, dbc->ring_evt, &dbc->erst, flags);
+       if (ret)
+               goto erst_fail;
+
+       /* Allocate context data structure: */
+       dbc->ctx = xhci_alloc_container_ctx(xhci, XHCI_CTX_TYPE_DEVICE, flags);
+       if (!dbc->ctx)
+               goto ctx_fail;
+
+       /* Allocate the string table: */
+       dbc->string_size = sizeof(struct dbc_strings);
+       dbc->string = dbc_dma_alloc_coherent(xhci,
+                                            dbc->string_size,
+                                            &dbc->string_dma,
+                                            flags);
+       if (!dbc->string)
+               goto string_fail;
+
+       /* Setup ERST register: */
+       writel(dbc->erst.erst_size, &dbc->regs->ersts);
+       xhci_write_64(xhci, dbc->erst.erst_dma_addr, &dbc->regs->erstba);
+       deq = xhci_trb_virt_to_dma(dbc->ring_evt->deq_seg,
+                                  dbc->ring_evt->dequeue);
+       xhci_write_64(xhci, deq, &dbc->regs->erdp);
+
+       /* Setup strings and contexts: */
+       string_length = xhci_dbc_populate_strings(dbc->string);
+       xhci_dbc_populate_contexts(xhci, string_length);
+
+       mmiowb();
+
+       ret = xhci_dbc_gadget_eps_init(xhci, flags);
+       if (ret)
+               goto eps_init_fail;
+
+       dbc->state = DS_INITIALIZED;
+
+       return 0;
+
+eps_init_fail:
+       dbc_dma_free_coherent(xhci,
+                             dbc->string_size,
+                             dbc->string, dbc->string_dma);
+       dbc->string = NULL;
+string_fail:
+       xhci_free_container_ctx(xhci, dbc->ctx);
+       dbc->ctx = NULL;
+ctx_fail:
+       xhci_free_erst(xhci, &dbc->erst);
+erst_fail:
+       xhci_ring_free(xhci, dbc->ring_out);
+       dbc->ring_out = NULL;
+out_fail:
+       xhci_ring_free(xhci, dbc->ring_in);
+       dbc->ring_in = NULL;
+in_fail:
+       xhci_ring_free(xhci, dbc->ring_evt);
+       dbc->ring_evt = NULL;
+evt_fail:
+       return -ENOMEM;
+}
+
+static void xhci_dbc_mem_cleanup(struct xhci_hcd *xhci)
+{
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       if (!dbc)
+               return;
+
+       xhci_dbc_gadget_eps_exit(xhci);
+
+       if (dbc->string) {
+               dbc_dma_free_coherent(xhci,
+                                     dbc->string_size,
+                                     dbc->string, dbc->string_dma);
+               dbc->string = NULL;
+       }
+
+       xhci_free_container_ctx(xhci, dbc->ctx);
+       dbc->ctx = NULL;
+
+       xhci_free_erst(xhci, &dbc->erst);
+       xhci_ring_free(xhci, dbc->ring_out);
+       xhci_ring_free(xhci, dbc->ring_in);
+       xhci_ring_free(xhci, dbc->ring_evt);
+       dbc->ring_in = NULL;
+       dbc->ring_out = NULL;
+       dbc->ring_evt = NULL;
+}
+
+static void xhci_dbc_reset_debug_port(struct xhci_hcd *xhci)
+{
+       u32                     val;
+       unsigned long           flags;
+       int                     port_index;
+       __le32 __iomem          **port_array;
+
+       spin_lock_irqsave(&xhci->lock, flags);
+
+       port_index = xhci->num_usb3_ports;
+       port_array = xhci->usb3_ports;
+       if (port_index <= 0) {
+               spin_unlock_irqrestore(&xhci->lock, flags);
+               return;
+       }
+
+       while (port_index--) {
+               val = readl(port_array[port_index]);
+               if (!(val & PORT_CONNECT))
+                       writel(val | PORT_RESET, port_array[port_index]);
+       }
+
+       spin_unlock_irqrestore(&xhci->lock, flags);
+}
+
+static int __xhci_dbc_start(struct xhci_hcd *xhci)
+{
+       int                     ret;
+       u32                     ctrl;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       if (dbc->state != DS_DISABLED)
+               return -EINVAL;
+
+       writel(0, &dbc->regs->control);
+       ret = xhci_handshake(&dbc->regs->control,
+                            DBC_CTRL_DBC_ENABLE,
+                            0, 1000);
+       if (ret)
+               return ret;
+
+       ret = xhci_dbc_mem_init(xhci, GFP_ATOMIC);
+       if (ret)
+               return ret;
+
+       ctrl = readl(&dbc->regs->control);
+       writel(ctrl | DBC_CTRL_DBC_ENABLE | DBC_CTRL_PORT_ENABLE,
+              &dbc->regs->control);
+       ret = xhci_handshake(&dbc->regs->control,
+                            DBC_CTRL_DBC_ENABLE,
+                            DBC_CTRL_DBC_ENABLE, 1000);
+       if (ret)
+               return ret;
+
+       xhci_dbc_reset_debug_port(xhci);
+       dbc->state = DS_ENABLED;
+
+       return 0;
+}
+
+static void __xhci_dbc_stop(struct xhci_hcd *xhci)
+{
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       if (dbc->state == DS_DISABLED)
+               return;
+
+       writel(0, &dbc->regs->control);
+       xhci_dbc_mem_cleanup(xhci);
+       dbc->state = DS_DISABLED;
+}
+
+static int xhci_dbc_start(struct xhci_hcd *xhci)
+{
+       int                     ret;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       WARN_ON(!dbc);
+
+       spin_lock(&dbc->lock);
+       ret = __xhci_dbc_start(xhci);
+       spin_unlock(&dbc->lock);
+
+       if (!ret) {
+               pm_runtime_get_sync(xhci_to_hcd(xhci)->self.controller);
+               ret = mod_delayed_work(system_wq, &dbc->event_work, 1);
+       }
+
+       return ret;
+}
+
+static void xhci_dbc_stop(struct xhci_hcd *xhci)
+{
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       WARN_ON(!dbc);
+
+       cancel_delayed_work_sync(&dbc->event_work);
+
+       if (dbc->gs_port_num != GSPORT_INVAL) {
+               gserial_disconnect(&dbc->gs_port);
+               gserial_free_line(dbc->gs_port_num);
+               dbc->gs_port_num = GSPORT_INVAL;
+       }
+
+       spin_lock(&dbc->lock);
+       __xhci_dbc_stop(xhci);
+       spin_unlock(&dbc->lock);
+
+       pm_runtime_put_sync(xhci_to_hcd(xhci)->self.controller);
+}
+
+static void
+dbc_handle_port_status(struct xhci_hcd *xhci, union xhci_trb *event)
+{
+       u32                     portsc;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       portsc = readl(&dbc->regs->portsc);
+       if (portsc & DBC_PORTSC_CONN_CHANGE)
+               xhci_info(xhci, "DbC port connect change\n");
+
+       if (portsc & DBC_PORTSC_RESET_CHANGE)
+               xhci_info(xhci, "DbC port reset change\n");
+
+       if (portsc & DBC_PORTSC_LINK_CHANGE)
+               xhci_info(xhci, "DbC port link status change\n");
+
+       if (portsc & DBC_PORTSC_CONFIG_CHANGE)
+               xhci_info(xhci, "DbC config error change\n");
+
+       /* Port reset change bit will be cleared in other place: */
+       writel(portsc & ~DBC_PORTSC_RESET_CHANGE, &dbc->regs->portsc);
+}
+
+static void dbc_handle_tx_event(struct xhci_hcd *xhci, union xhci_trb *event)
+{
+       struct dbc_ep           *dep;
+       struct usb_request      *req;
+       struct xhci_ring        *ring;
+       int                     ep_id;
+       int                     status;
+       u32                     comp_code;
+       size_t                  remain_length;
+       struct dbc_request      *dreq = NULL, *r;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       comp_code       = GET_COMP_CODE(le32_to_cpu(event->generic.field[2]));
+       remain_length   = EVENT_TRB_LEN(le32_to_cpu(event->generic.field[2]));
+       ep_id           = TRB_TO_EP_ID(le32_to_cpu(event->generic.field[3]));
+       dep             = (ep_id == EPID_OUT) ?
+                               dbc->eps[BULK_OUT] : dbc->eps[BULK_IN];
+       ring            = dep->ring;
+
+       switch (comp_code) {
+       case COMP_SUCCESS:
+               remain_length = 0;
+       /* FALLTHROUGH */
+       case COMP_SHORT_PACKET:
+               status = 0;
+               break;
+       case COMP_TRB_ERROR:
+       case COMP_BABBLE_DETECTED_ERROR:
+       case COMP_USB_TRANSACTION_ERROR:
+       case COMP_STALL_ERROR:
+               xhci_warn(xhci, "tx error %d detected\n", comp_code);
+               status = -comp_code;
+               break;
+       default:
+               xhci_err(xhci, "unknown tx error %d\n", comp_code);
+               status = -comp_code;
+               break;
+       }
+
+       /* Match the pending request: */
+       list_for_each_entry(r, &dep->pending_list, list) {
+               if (r->trb_dma == event->trans_event.buffer) {
+                       dreq = r;
+                       break;
+               }
+       }
+
+       if (!dreq) {
+               xhci_warn(xhci, "no matched request\n");
+               return;
+       }
+
+       trace_xhci_dbc_handle_transfer(ring, &dreq->trb->generic);
+
+       req = &dreq->request;
+       ring->num_trbs_free++;
+       req->actual = req->length - remain_length;
+       xhci_dbc_giveback(dreq, status);
+}
+
+static enum evtreturn __xhci_dbc_handle_events(struct xhci_dbc *dbc)
+{
+       dma_addr_t              deq;
+       struct dbc_ep           *dep;
+       union xhci_trb          *evt;
+       u32                     ctrl, portsc;
+       struct xhci_hcd         *xhci = dbc->xhci;
+       bool                    update_erdp = false;
+
+       /* DbC state machine: */
+       switch (dbc->state) {
+       case DS_DISABLED:
+       case DS_INITIALIZED:
+
+               return EVT_ERR;
+       case DS_ENABLED:
+               portsc = readl(&dbc->regs->portsc);
+               if (portsc & DBC_PORTSC_CONN_STATUS) {
+                       dbc->state = DS_CONNECTED;
+                       xhci_info(xhci, "DbC connected\n");
+               }
+
+               return EVT_DONE;
+       case DS_CONNECTED:
+               ctrl = readl(&dbc->regs->control);
+               if (ctrl & DBC_CTRL_DBC_RUN) {
+                       dbc->state = DS_CONFIGURED;
+                       xhci_info(xhci, "DbC configured\n");
+                       portsc = readl(&dbc->regs->portsc);
+                       writel(portsc, &dbc->regs->portsc);
+                       return EVT_GSER;
+               }
+
+               return EVT_DONE;
+       case DS_CONFIGURED:
+               /* Handle cable unplug event: */
+               portsc = readl(&dbc->regs->portsc);
+               if (!(portsc & DBC_PORTSC_PORT_ENABLED) &&
+                   !(portsc & DBC_PORTSC_CONN_STATUS)) {
+                       xhci_info(xhci, "DbC cable unplugged\n");
+                       dbc->state = DS_ENABLED;
+                       xhci_dbc_flush_reqests(dbc);
+
+                       return EVT_DISC;
+               }
+
+               /* Handle debug port reset event: */
+               if (portsc & DBC_PORTSC_RESET_CHANGE) {
+                       xhci_info(xhci, "DbC port reset\n");
+                       writel(portsc, &dbc->regs->portsc);
+                       dbc->state = DS_ENABLED;
+                       xhci_dbc_flush_reqests(dbc);
+
+                       return EVT_DISC;
+               }
+
+               /* Handle endpoint stall event: */
+               ctrl = readl(&dbc->regs->control);
+               if ((ctrl & DBC_CTRL_HALT_IN_TR) ||
+                   (ctrl & DBC_CTRL_HALT_OUT_TR)) {
+                       xhci_info(xhci, "DbC Endpoint stall\n");
+                       dbc->state = DS_STALLED;
+
+                       if (ctrl & DBC_CTRL_HALT_IN_TR) {
+                               dep = dbc->eps[BULK_IN];
+                               xhci_dbc_flush_endpoint_requests(dep);
+                       }
+
+                       if (ctrl & DBC_CTRL_HALT_OUT_TR) {
+                               dep = dbc->eps[BULK_OUT];
+                               xhci_dbc_flush_endpoint_requests(dep);
+                       }
+
+                       return EVT_DONE;
+               }
+
+               /* Clear DbC run change bit: */
+               if (ctrl & DBC_CTRL_DBC_RUN_CHANGE) {
+                       writel(ctrl, &dbc->regs->control);
+                       ctrl = readl(&dbc->regs->control);
+               }
+
+               break;
+       case DS_STALLED:
+               ctrl = readl(&dbc->regs->control);
+               if (!(ctrl & DBC_CTRL_HALT_IN_TR) &&
+                   !(ctrl & DBC_CTRL_HALT_OUT_TR) &&
+                   (ctrl & DBC_CTRL_DBC_RUN)) {
+                       dbc->state = DS_CONFIGURED;
+                       break;
+               }
+
+               return EVT_DONE;
+       default:
+               xhci_err(xhci, "Unknown DbC state %d\n", dbc->state);
+               break;
+       }
+
+       /* Handle the events in the event ring: */
+       evt = dbc->ring_evt->dequeue;
+       while ((le32_to_cpu(evt->event_cmd.flags) & TRB_CYCLE) ==
+                       dbc->ring_evt->cycle_state) {
+               /*
+                * Add a barrier between reading the cycle flag and any
+                * reads of the event's flags/data below:
+                */
+               rmb();
+
+               trace_xhci_dbc_handle_event(dbc->ring_evt, &evt->generic);
+
+               switch (le32_to_cpu(evt->event_cmd.flags) & TRB_TYPE_BITMASK) {
+               case TRB_TYPE(TRB_PORT_STATUS):
+                       dbc_handle_port_status(xhci, evt);
+                       break;
+               case TRB_TYPE(TRB_TRANSFER):
+                       dbc_handle_tx_event(xhci, evt);
+                       break;
+               default:
+                       break;
+               }
+
+               inc_deq(xhci, dbc->ring_evt);
+               evt = dbc->ring_evt->dequeue;
+               update_erdp = true;
+       }
+
+       /* Update event ring dequeue pointer: */
+       if (update_erdp) {
+               deq = xhci_trb_virt_to_dma(dbc->ring_evt->deq_seg,
+                                          dbc->ring_evt->dequeue);
+               xhci_write_64(xhci, deq, &dbc->regs->erdp);
+       }
+
+       return EVT_DONE;
+}
+
+static void xhci_dbc_handle_events(struct work_struct *work)
+{
+       int                     ret;
+       enum evtreturn          evtr;
+       struct xhci_dbc         *dbc;
+       struct xhci_hcd         *xhci;
+
+       dbc = container_of(to_delayed_work(work), struct xhci_dbc, event_work);
+       xhci = dbc->xhci;
+
+       spin_lock(&dbc->lock);
+       evtr = __xhci_dbc_handle_events(dbc);
+       spin_unlock(&dbc->lock);
+
+       switch (evtr) {
+       case EVT_GSER:
+               ret = gserial_alloc_line(&dbc->gs_port_num);
+               if (ret) {
+                       xhci_err(xhci, "failed to alloc tty line\n");
+                       break;
+               }
+
+               ret = gserial_connect(&dbc->gs_port, dbc->gs_port_num);
+               if (ret) {
+                       xhci_err(xhci, "failed to register DbC tty\n");
+                       gserial_free_line(dbc->gs_port_num);
+                       dbc->gs_port_num = GSPORT_INVAL;
+                       break;
+               }
+               xhci_info(xhci, "DbC now attached to /dev/ttyGS%d\n",
+                         dbc->gs_port_num);
+               mod_delayed_work(system_wq, &dbc->event_work, 1);
+               break;
+       case EVT_DISC:
+               gserial_disconnect(&dbc->gs_port);
+               gserial_free_line(dbc->gs_port_num);
+               dbc->gs_port_num = GSPORT_INVAL;
+
+               mod_delayed_work(system_wq, &dbc->event_work, 1);
+               break;
+       case EVT_DONE:
+               mod_delayed_work(system_wq, &dbc->event_work, 1);
+               break;
+       default:
+               xhci_info(xhci, "stop handling dbc events\n");
+       }
+}
+
+static void xhci_dbc_exit(struct xhci_hcd *xhci)
+{
+       unsigned long           flags;
+
+       spin_lock_irqsave(&xhci->lock, flags);
+       kfree(xhci->dbc);
+       xhci->dbc = NULL;
+       spin_unlock_irqrestore(&xhci->lock, flags);
+}
+
+static int xhci_dbc_init(struct xhci_hcd *xhci)
+{
+       u32                     reg;
+       struct xhci_dbc         *dbc;
+       unsigned long           flags;
+       void __iomem            *base;
+       int                     dbc_cap_offs;
+
+       base = &xhci->cap_regs->hc_capbase;
+       dbc_cap_offs = xhci_find_next_ext_cap(base, 0, XHCI_EXT_CAPS_DEBUG);
+       if (!dbc_cap_offs)
+               return -ENODEV;
+
+       dbc = kzalloc(sizeof(*dbc), GFP_KERNEL);
+       if (!dbc)
+               return -ENOMEM;
+
+       dbc->regs = base + dbc_cap_offs;
+
+       /* We will avoid using DbC in xhci driver if it's in use. */
+       reg = readl(&dbc->regs->control);
+       if (reg & DBC_CTRL_DBC_ENABLE) {
+               kfree(dbc);
+               return -EBUSY;
+       }
+
+       spin_lock_irqsave(&xhci->lock, flags);
+       if (xhci->dbc) {
+               spin_unlock_irqrestore(&xhci->lock, flags);
+               kfree(dbc);
+               return -EBUSY;
+       }
+       xhci->dbc = dbc;
+       spin_unlock_irqrestore(&xhci->lock, flags);
+
+       dbc->xhci = xhci;
+       INIT_DELAYED_WORK(&dbc->event_work, xhci_dbc_handle_events);
+       spin_lock_init(&dbc->lock);
+       dbc->gs_port_num = GSPORT_INVAL;
+
+       return 0;
+}
+
+static ssize_t dbc_show(struct device *dev,
+                       struct device_attribute *attr,
+                       char *buf)
+{
+       const char              *p;
+       struct xhci_dbc         *dbc;
+       struct xhci_hcd         *xhci;
+
+       xhci = hcd_to_xhci(dev_get_drvdata(dev));
+       dbc = xhci->dbc;
+
+       switch (dbc->state) {
+       case DS_DISABLED:
+               p = "disabled";
+               break;
+       case DS_INITIALIZED:
+               p = "initialized";
+               break;
+       case DS_ENABLED:
+               p = "enabled";
+               break;
+       case DS_CONNECTED:
+               p = "connected";
+               break;
+       case DS_CONFIGURED:
+               p = "configured";
+               break;
+       case DS_STALLED:
+               p = "stalled";
+               break;
+       default:
+               p = "unknown";
+       }
+
+       return sprintf(buf, "%s\n", p);
+}
+
+static ssize_t dbc_store(struct device *dev,
+                        struct device_attribute *attr,
+                        const char *buf, size_t count)
+{
+       struct xhci_dbc         *dbc;
+       struct xhci_hcd         *xhci;
+
+       xhci = hcd_to_xhci(dev_get_drvdata(dev));
+       dbc = xhci->dbc;
+
+       if (!strncmp(buf, "enable", 6))
+               xhci_dbc_start(xhci);
+       else if (!strncmp(buf, "disable", 7))
+               xhci_dbc_stop(xhci);
+       else
+               return -EINVAL;
+
+       return count;
+}
+
+static DEVICE_ATTR(dbc, 0644, dbc_show, dbc_store);
+
+int dbc_create_sysfs_file(struct xhci_hcd *xhci)
+{
+       int                     ret;
+       struct device           *dev = xhci_to_hcd(xhci)->self.controller;
+
+       ret = xhci_dbc_init(xhci);
+       if (ret)
+               return ret;
+
+       return device_create_file(dev, &dev_attr_dbc);
+}
+
+void dbc_remove_sysfs_file(struct xhci_hcd *xhci)
+{
+       struct device           *dev = xhci_to_hcd(xhci)->self.controller;
+
+       device_remove_file(dev, &dev_attr_dbc);
+       xhci_dbc_stop(xhci);
+       xhci_dbc_exit(xhci);
+}
+
+#ifdef CONFIG_PM
+int xhci_dbc_suspend(struct xhci_hcd *xhci)
+{
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       if (!dbc)
+               return 0;
+
+       if (dbc->state == DS_CONFIGURED)
+               dbc->resume_required = 1;
+
+       xhci_dbc_stop(xhci);
+
+       return 0;
+}
+
+int xhci_dbc_resume(struct xhci_hcd *xhci)
+{
+       int                     ret = 0;
+       struct xhci_dbc         *dbc = xhci->dbc;
+
+       if (!dbc)
+               return 0;
+
+       if (dbc->resume_required) {
+               dbc->resume_required = 0;
+               xhci_dbc_start(xhci);
+       }
+
+       return ret;
+}
+#endif /* CONFIG_PM */
diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h
new file mode 100644
index 0000000..4df8db3
--- /dev/null
+++ b/drivers/usb/host/xhci-dbgcap.h
@@ -0,0 +1,194 @@
+
+/**
+ * xhci-dbgcap.h - xHCI debug capability support
+ *
+ * Copyright (C) 2017 Intel Corporation
+ *
+ * Author: Lu Baolu <baolu...@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_DBGCAP_H
+#define __LINUX_XHCI_DBGCAP_H
+
+#include <linux/usb/gadget.h>
+#include <linux/usb/u_serial.h>
+
+struct dbc_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 */
+};
+
+struct dbc_info_context {
+       __le64  string0;
+       __le64  manufacturer;
+       __le64  product;
+       __le64  serial;
+       __le32  length;
+       __le32  __reserved_0[7];
+};
+
+#define DBC_CTRL_DBC_RUN               BIT(0)
+#define DBC_CTRL_PORT_ENABLE           BIT(1)
+#define DBC_CTRL_HALT_OUT_TR           BIT(2)
+#define DBC_CTRL_HALT_IN_TR            BIT(3)
+#define DBC_CTRL_DBC_RUN_CHANGE                BIT(4)
+#define DBC_CTRL_DBC_ENABLE            BIT(31)
+#define DBC_CTRL_MAXBURST(p)           (((p) >> 16) & 0xff)
+#define DBC_DOOR_BELL_TARGET(p)                (((p) & 0xff) << 8)
+
+#define DBC_MAX_PACKET                 1024
+#define DBC_MAX_STRING_LENGTH          64
+#define DBC_STRING_MANUFACTURER                "Linux"
+#define DBC_STRING_PRODUCT             "Remote GDB"
+#define DBC_STRING_SERIAL              "0001"
+#define        DBC_CONTEXT_SIZE                64
+
+/*
+ * Port status:
+ */
+#define DBC_PORTSC_CONN_STATUS         BIT(0)
+#define DBC_PORTSC_PORT_ENABLED                BIT(1)
+#define DBC_PORTSC_CONN_CHANGE         BIT(17)
+#define DBC_PORTSC_RESET_CHANGE                BIT(21)
+#define DBC_PORTSC_LINK_CHANGE         BIT(22)
+#define DBC_PORTSC_CONFIG_CHANGE       BIT(23)
+
+struct dbc_strings {
+       char    string0[DBC_MAX_STRING_LENGTH];
+       char    manufacturer[DBC_MAX_STRING_LENGTH];
+       char    product[DBC_MAX_STRING_LENGTH];
+       char    serial[DBC_MAX_STRING_LENGTH];
+};
+
+#define DBC_PROTOCOL                   1       /* GNU Remote Debug Command */
+#define DBC_VENDOR_ID                  0x1d6b  /* Linux Foundation 0x1d6b */
+#define DBC_PRODUCT_ID                 0x0004  /* device 0004 */
+#define DBC_DEVICE_REV                 0x0010  /* 0.10 */
+
+enum dbc_state {
+       DS_DISABLED = 0,
+       DS_INITIALIZED,
+       DS_ENABLED,
+       DS_CONNECTED,
+       DS_CONFIGURED,
+       DS_STALLED,
+};
+
+struct dbc_ep {
+       struct usb_ep                   ep;
+       struct xhci_dbc                 *dbc;
+       struct list_head                pending_list;
+       struct xhci_ring                *ring;
+
+       unsigned                        direction:1;
+};
+
+struct dbc_request {
+       struct usb_request              request;
+       struct dbc_ep                   *dep;
+       struct list_head                list;
+       dma_addr_t                      trb_dma;
+       union xhci_trb                  *trb;
+
+       unsigned                        direction:1;
+};
+
+#define ep_to_dep(e)           (container_of(e, struct dbc_ep, ep))
+#define req_to_dreq(r)         (container_of(r, struct dbc_request, request))
+
+/*
+ * Private structure for DbC hardware state:
+ */
+struct xhci_dbc {
+       struct xhci_hcd                 *xhci;
+       struct dbc_regs __iomem         *regs;
+       struct xhci_ring                *ring_evt;
+       struct xhci_ring                *ring_in;
+       struct xhci_ring                *ring_out;
+       struct xhci_erst                erst;
+       struct xhci_container_ctx       *ctx;
+
+       struct dbc_strings              *string;
+       dma_addr_t                      string_dma;
+       size_t                          string_size;
+
+       enum dbc_state                  state;
+       struct delayed_work             event_work;
+       unsigned                        resume_required:1;
+
+       unsigned char                   gs_port_num;
+       struct gserial                  gs_port;
+       struct dbc_ep                   *eps[2];
+
+       /* device lock */
+       spinlock_t                      lock;
+};
+
+#define dbc_bulkout_ctx(d)             \
+       ((struct xhci_ep_ctx *)((d)->ctx->bytes + DBC_CONTEXT_SIZE))
+#define dbc_bulkin_ctx(d)              \
+       ((struct xhci_ep_ctx *)((d)->ctx->bytes + DBC_CONTEXT_SIZE * 2))
+#define dbc_bulkout_enq(d)             \
+       xhci_trb_virt_to_dma((d)->ring_out->enq_seg, (d)->ring_out->enqueue)
+#define dbc_bulkin_enq(d)              \
+       xhci_trb_virt_to_dma((d)->ring_in->enq_seg, (d)->ring_in->enqueue)
+#define dbc_epctx_info2(t, p, b)       \
+       cpu_to_le32(EP_TYPE(t) | MAX_PACKET(p) | MAX_BURST(b))
+#define dbc_ep_dma_direction(d)                \
+       ((d)->direction ? DMA_FROM_DEVICE : DMA_TO_DEVICE)
+
+#define GSPORT_INVAL                   ((unsigned char)(-1))
+#define BULK_OUT                       0
+#define BULK_IN                                1
+#define EPID_OUT                       2
+#define EPID_IN                                3
+
+enum evtreturn {
+       EVT_ERR = -1,
+       EVT_DONE,
+       EVT_GSER,
+       EVT_DISC,
+};
+
+#ifdef CONFIG_USB_XHCI_DBGCAP
+int dbc_create_sysfs_file(struct xhci_hcd *xhci);
+void dbc_remove_sysfs_file(struct xhci_hcd *xhci);
+#ifdef CONFIG_PM
+int xhci_dbc_suspend(struct xhci_hcd *xhci);
+int xhci_dbc_resume(struct xhci_hcd *xhci);
+#endif /* CONFIG_PM */
+#else
+static inline int dbc_create_sysfs_file(struct xhci_hcd *xhci)
+{
+       return 0;
+}
+
+static inline void dbc_remove_sysfs_file(struct xhci_hcd *xhci)
+{
+}
+
+static inline int xhci_dbc_suspend(struct xhci_hcd *xhci)
+{
+       return 0;
+}
+
+static inline int xhci_dbc_resume(struct xhci_hcd *xhci)
+{
+       return 0;
+}
+#endif /* CONFIG_USB_XHCI_DBGCAP */
+#endif /* __LINUX_XHCI_DBGCAP_H */
diff --git a/drivers/usb/host/xhci-trace.h b/drivers/usb/host/xhci-trace.h
index 8ce96de..5b3b1b0 100644
--- a/drivers/usb/host/xhci-trace.h
+++ b/drivers/usb/host/xhci-trace.h
@@ -26,6 +26,7 @@
 
 #include <linux/tracepoint.h>
 #include "xhci.h"
+#include "xhci-dbgcap.h"
 
 #define XHCI_MSG_MAX   500
 
@@ -158,6 +159,21 @@ DEFINE_EVENT(xhci_log_trb, xhci_queue_trb,
        TP_ARGS(ring, trb)
 );
 
+DEFINE_EVENT(xhci_log_trb, xhci_dbc_handle_event,
+       TP_PROTO(struct xhci_ring *ring, struct xhci_generic_trb *trb),
+       TP_ARGS(ring, trb)
+);
+
+DEFINE_EVENT(xhci_log_trb, xhci_dbc_handle_transfer,
+       TP_PROTO(struct xhci_ring *ring, struct xhci_generic_trb *trb),
+       TP_ARGS(ring, trb)
+);
+
+DEFINE_EVENT(xhci_log_trb, xhci_dbc_gadget_ep_queue,
+       TP_PROTO(struct xhci_ring *ring, struct xhci_generic_trb *trb),
+       TP_ARGS(ring, trb)
+);
+
 DECLARE_EVENT_CLASS(xhci_log_virt_dev,
        TP_PROTO(struct xhci_virt_device *vdev),
        TP_ARGS(vdev),
@@ -453,6 +469,55 @@ DEFINE_EVENT(xhci_log_ring, xhci_inc_deq,
        TP_PROTO(struct xhci_ring *ring),
        TP_ARGS(ring)
 );
+
+DECLARE_EVENT_CLASS(xhci_dbc_log_request,
+       TP_PROTO(struct dbc_request *req),
+       TP_ARGS(req),
+       TP_STRUCT__entry(
+               __dynamic_array(char, name, XHCI_MSG_MAX)
+               __field(struct dbc_request *, req)
+               __field(unsigned int, actual)
+               __field(unsigned int, length)
+               __field(int, status)
+       ),
+       TP_fast_assign(
+               snprintf(__get_str(name), XHCI_MSG_MAX,
+                        "%s", req->dep->ep.name);
+               __entry->req = req;
+               __entry->actual = req->request.actual;
+               __entry->length = req->request.length;
+               __entry->status = req->request.status;
+       ),
+       TP_printk("%s: req %p length %u/%u ==> %d",
+               __get_str(name), __entry->req, __entry->actual,
+               __entry->length, __entry->status
+       )
+);
+
+DEFINE_EVENT(xhci_dbc_log_request, xhci_dbc_alloc_request,
+       TP_PROTO(struct dbc_request *req),
+       TP_ARGS(req)
+);
+
+DEFINE_EVENT(xhci_dbc_log_request, xhci_dbc_free_request,
+       TP_PROTO(struct dbc_request *req),
+       TP_ARGS(req)
+);
+
+DEFINE_EVENT(xhci_dbc_log_request, xhci_dbc_queue_request,
+       TP_PROTO(struct dbc_request *req),
+       TP_ARGS(req)
+);
+
+DEFINE_EVENT(xhci_dbc_log_request, xhci_dbc_dequeue_request,
+       TP_PROTO(struct dbc_request *req),
+       TP_ARGS(req)
+);
+
+DEFINE_EVENT(xhci_dbc_log_request, xhci_dbc_giveback_request,
+       TP_PROTO(struct dbc_request *req),
+       TP_ARGS(req)
+);
 #endif /* __XHCI_TRACE_H */
 
 /* this part must be outside header guard */
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index b2ff1ff..39a9a88 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -32,6 +32,7 @@
 #include "xhci.h"
 #include "xhci-trace.h"
 #include "xhci-mtk.h"
+#include "xhci-dbgcap.h"
 
 #define DRIVER_AUTHOR "Sarah Sharp"
 #define DRIVER_DESC "'eXtensible' Host Controller (xHC) Driver"
@@ -632,6 +633,9 @@ int xhci_run(struct usb_hcd *hcd)
        }
        xhci_dbg_trace(xhci, trace_xhci_dbg_init,
                        "Finished xhci_run for USB2 roothub");
+
+       dbc_create_sysfs_file(xhci);
+
        return 0;
 }
 EXPORT_SYMBOL_GPL(xhci_run);
@@ -660,6 +664,8 @@ static void xhci_stop(struct usb_hcd *hcd)
                return;
        }
 
+       dbc_remove_sysfs_file(xhci);
+
        spin_lock_irq(&xhci->lock);
        xhci->xhc_state |= XHCI_STATE_HALTED;
        xhci->cmd_ring_state = CMD_RING_STATE_STOPPED;
@@ -876,6 +882,8 @@ int xhci_suspend(struct xhci_hcd *xhci, bool do_wakeup)
                        xhci->shared_hcd->state != HC_STATE_SUSPENDED)
                return -EINVAL;
 
+       xhci_dbc_suspend(xhci);
+
        /* Clear root port wake on bits if wakeup not allowed. */
        if (!do_wakeup)
                xhci_disable_port_wake_on_bits(xhci);
@@ -1071,6 +1079,8 @@ int xhci_resume(struct xhci_hcd *xhci, bool hibernated)
 
        spin_unlock_irq(&xhci->lock);
 
+       xhci_dbc_resume(xhci);
+
  done:
        if (retval == 0) {
                /* Resume root hubs only when have pending events. */
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 62bcdcd..bae2538 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1850,6 +1850,7 @@ struct xhci_hcd {
 /* Compliance Mode Timer Triggered every 2 seconds */
 #define COMP_MODE_RCVRY_MSECS 2000
 
+       void                    *dbc;
        /* platform-specific data -- must come last */
        unsigned long           priv[0] __aligned(sizeof(s64));
 };
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 1a4a4ba..e93ada1 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -243,6 +243,58 @@ int usb_ep_clear_halt(struct usb_ep *ep);
 int usb_ep_set_wedge(struct usb_ep *ep);
 int usb_ep_fifo_status(struct usb_ep *ep);
 void usb_ep_fifo_flush(struct usb_ep *ep);
+#elif IS_ENABLED(CONFIG_USB_XHCI_DBGCAP)
+static inline void usb_ep_set_maxpacket_limit(struct usb_ep *ep,
+               unsigned maxpacket_limit)
+{ }
+static inline int usb_ep_enable(struct usb_ep *ep)
+{
+       int ret = 0;
+
+       ret = ep->ops->enable(ep, ep->desc);
+       if (!ret)
+               ep->enabled = true;
+
+       return ret;
+}
+static inline int usb_ep_disable(struct usb_ep *ep)
+{
+       int ret = 0;
+
+       ret = ep->ops->disable(ep);
+       if (!ret)
+               ep->enabled = false;
+
+       return ret;
+}
+static inline struct usb_request *usb_ep_alloc_request(struct usb_ep *ep,
+               gfp_t gfp_flags)
+{
+       return ep->ops->alloc_request(ep, gfp_flags);
+}
+
+static inline void usb_ep_free_request(struct usb_ep *ep,
+               struct usb_request *req)
+{
+       ep->ops->free_request(ep, req);
+}
+static inline int usb_ep_queue(struct usb_ep *ep, struct usb_request *req,
+               gfp_t gfp_flags)
+{
+       return ep->ops->queue(ep, req, gfp_flags);
+}
+static inline int usb_ep_dequeue(struct usb_ep *ep, struct usb_request *req)
+{ return 0; }
+static inline int usb_ep_set_halt(struct usb_ep *ep)
+{ return 0; }
+static inline int usb_ep_clear_halt(struct usb_ep *ep)
+{ return 0; }
+static inline int usb_ep_set_wedge(struct usb_ep *ep)
+{ return 0; }
+static inline int usb_ep_fifo_status(struct usb_ep *ep)
+{ return 0; }
+static inline void usb_ep_fifo_flush(struct usb_ep *ep)
+{ }
 #else
 static inline void usb_ep_set_maxpacket_limit(struct usb_ep *ep,
                unsigned maxpacket_limit)
-- 
2.7.4

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