Commit aeb9dd1d authored by Lu Baolu's avatar Lu Baolu Committed by Ingo Molnar
Browse files

usb/early: Add driver for xhci debug capability 



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 the xHCI host. There isn't any precondition
from the xHCI host side for the DbC to work.

One use for this feature is kernel debugging, for example
when your machine crashes very early before the regular
console code is initialized. Other uses include simpler,
lockless logging instead of a full-blown printk console
driver and klogd.

Signed-off-by: default avatarLu Baolu <baolu.lu@linux.intel.com>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-usb@vger.kernel.org
Link: http://lkml.kernel.org/r/1490083293-3792-3-git-send-email-baolu.lu@linux.intel.com


[ Small fix to the Kconfig help text. ]
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent dd759d93

arch/x86/Kconfig.debug

+25 −2
Original line number Diff line number Diff line
@@ -5,6 +5,9 @@ config TRACE_IRQFLAGS_SUPPORT 


source "lib/Kconfig.debug"



config EARLY_PRINTK_USB

	bool



config X86_VERBOSE_BOOTUP

	bool "Enable verbose x86 bootup info messages"

	default y
@@ -23,19 +26,20 @@ config EARLY_PRINTK 
	  This is useful for kernel debugging when your machine crashes very

	  early before the console code is initialized. For normal operation

	  it is not recommended because it looks ugly and doesn't cooperate

	  with klogd/syslogd or the X server. You should normally N here,

	  with klogd/syslogd or the X server. You should normally say N here,

	  unless you want to debug such a crash.



config EARLY_PRINTK_DBGP

	bool "Early printk via EHCI debug port"

	depends on EARLY_PRINTK && PCI

	select EARLY_PRINTK_USB

	---help---

	  Write kernel log output directly into the EHCI debug port.



	  This is useful for kernel debugging when your machine crashes very

	  early before the console code is initialized. For normal operation

	  it is not recommended because it looks ugly and doesn't cooperate

	  with klogd/syslogd or the X server. You should normally N here,

	  with klogd/syslogd or the X server. You should normally say N here,

	  unless you want to debug such a crash. You need usb debug device.



config EARLY_PRINTK_EFI
@@ -48,6 +52,25 @@ config EARLY_PRINTK_EFI 
	  This is useful for kernel debugging when your machine crashes very

	  early before the console code is initialized.



config EARLY_PRINTK_USB_XDBC

	bool "Early printk via the xHCI debug port"

	depends on EARLY_PRINTK && PCI

	select EARLY_PRINTK_USB

	---help---

	  Write kernel log output directly into the xHCI debug port.



	  One use for this feature is kernel debugging, for example when your

	  machine crashes very early before the regular console code is

	  initialized. Other uses include simpler, lockless logging instead of

	  a full-blown printk console driver + klogd.



	  For normal production environments this is normally not recommended,

	  because it doesn't feed events into klogd/syslogd and doesn't try to

	  print anything on the screen.



	  You should normally say N here, unless you want to debug early

	  crashes or need a very simple printk logging facility.



config X86_PTDUMP_CORE

	def_bool n

drivers/usb/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -49,7 +49,7 @@ obj-$(CONFIG_USB_MICROTEK) += image/ 
obj-$(CONFIG_USB_SERIAL)	+= serial/



obj-$(CONFIG_USB)		+= misc/

obj-$(CONFIG_EARLY_PRINTK_DBGP)	+= early/

obj-$(CONFIG_EARLY_PRINTK_USB)	+= early/



obj-$(CONFIG_USB_ATM)		+= atm/

obj-$(CONFIG_USB_SPEEDTOUCH)	+= atm/

drivers/usb/early/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -3,3 +3,4 @@ 
#



obj-$(CONFIG_EARLY_PRINTK_DBGP) += ehci-dbgp.o

obj-$(CONFIG_EARLY_PRINTK_USB_XDBC) += xhci-dbc.o

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