[PATCH v7 0/5] usb: early: add support for early printk through USB3 debug port

[Lu Baolu <baolu.lu@linux.intel.com>]

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.

---
Change log:
v6->v7:
  - add a new patch "[PATCH 1/5] x86: add simple udelay
    calibration" to make udelay() work for early drivers.
  - [PATCH 2/5] usb: dbc: early driver for xhci debug capability
    - add a kernel thread to handle error cases, such as cable
      unplugging.
    - Fixed several code styles pointed out by Ingo.

v5->v6:
  - rebase the patches on top of the latest 4.10-rc4
  - run successfully in a 32-bit kernel
  - [PATCH 1/4]
    - remove ugly linebreaks to make code more readable
    - rename config names to make them consistency
    - move sleep-able ioremap() out of the lock area
    - rename reserved fields of register structures
    - make the vertical tabulation of struct fields consistent
  - [PATCH 2/4]
    - remove "#ifdef" in the generic code by creating proper
      wrappers in header file
  - [PATCH 3/4]
    - refine the title and commit message
  - [PATCH 4/4]
    - fix several typos and grammar errors in the document

v4->v5:
  - add raw_spin_lock to make xdbc_bulk_write() reentrant.

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 (5):
  x86: add simple udelay calibration
  usb: dbc: early driver for xhci debug capability
  x86: add support for earlyprintk via USB3 debug port
  usb: serial: add dbc debug device support to usb_debug
  usb: doc: add document for USB3 debug port usage

 Documentation/admin-guide/kernel-parameters.txt |    1 +
 Documentation/usb/usb3-debug-port.rst           |   98 +++
 arch/x86/Kconfig.debug                          |   17 +
 arch/x86/kernel/early_printk.c                  |    5 +
 arch/x86/kernel/setup.c                         |   26 +
 drivers/usb/Kconfig                             |    3 +
 drivers/usb/Makefile                            |    2 +-
 drivers/usb/early/Makefile                      |    1 +
 drivers/usb/early/xhci-dbc.c                    | 1026 +++++++++++++++++++++++
 drivers/usb/early/xhci-dbc.h                    |  210 +++++
 drivers/usb/serial/usb_debug.c                  |   28 +-
 include/linux/usb/xhci-dbgp.h                   |   29 +
 12 files changed, 1442 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