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: 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.txt | 87 +++ 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 | 1097 +++++++++++++++++++++++++++++++++ drivers/usb/early/xhci-dbc.h | 206 +++++++ drivers/usb/serial/usb_debug.c | 28 +- include/linux/usb/xhci-dbgp.h | 22 + 12 files changed, 1469 insertions(+), 4 deletions(-) create mode 100644 Documentation/usb/usb3-debug-port.txt 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