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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: Lu Baolu <[email protected]> Acked-by: Thomas Gleixner <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Mathias Nyman <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] [ Small fix to the Kconfig help text. ] Signed-off-by: Ingo Molnar <[email protected]>
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Lines changed: 1281 additions & 3 deletions

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‎arch/x86/Kconfig.debug‎

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@@ -5,6 +5,9 @@ config TRACE_IRQFLAGS_SUPPORT
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source "lib/Kconfig.debug"
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config EARLY_PRINTK_USB
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bool
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config X86_VERBOSE_BOOTUP
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bool "Enable verbose x86 bootup info messages"
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default y
@@ -23,19 +26,20 @@ config EARLY_PRINTK
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This is useful for kernel debugging when your machine crashes very
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early before the console code is initialized. For normal operation
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it is not recommended because it looks ugly and doesn't cooperate
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with klogd/syslogd or the X server. You should normally N here,
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with klogd/syslogd or the X server. You should normally say N here,
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unless you want to debug such a crash.
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config EARLY_PRINTK_DBGP
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bool "Early printk via EHCI debug port"
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depends on EARLY_PRINTK && PCI
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select EARLY_PRINTK_USB
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---help---
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Write kernel log output directly into the EHCI debug port.
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This is useful for kernel debugging when your machine crashes very
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early before the console code is initialized. For normal operation
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it is not recommended because it looks ugly and doesn't cooperate
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with klogd/syslogd or the X server. You should normally N here,
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with klogd/syslogd or the X server. You should normally say N here,
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unless you want to debug such a crash. You need usb debug device.
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config EARLY_PRINTK_EFI
@@ -48,6 +52,25 @@ config EARLY_PRINTK_EFI
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This is useful for kernel debugging when your machine crashes very
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early before the console code is initialized.
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config EARLY_PRINTK_USB_XDBC
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bool "Early printk via the xHCI debug port"
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depends on EARLY_PRINTK && PCI
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select EARLY_PRINTK_USB
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---help---
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Write kernel log output directly into the xHCI debug port.
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One use for this feature is kernel debugging, for example when your
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machine crashes very early before the regular console code is
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initialized. Other uses include simpler, lockless logging instead of
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a full-blown printk console driver + klogd.
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For normal production environments this is normally not recommended,
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because it doesn't feed events into klogd/syslogd and doesn't try to
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print anything on the screen.
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You should normally say N here, unless you want to debug early
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crashes or need a very simple printk logging facility.
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config X86_PTDUMP_CORE
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def_bool n
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‎drivers/usb/Makefile‎

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@@ -49,7 +49,7 @@ obj-$(CONFIG_USB_MICROTEK) += image/
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obj-$(CONFIG_USB_SERIAL) += serial/
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obj-$(CONFIG_USB) += misc/
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obj-$(CONFIG_EARLY_PRINTK_DBGP) += early/
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obj-$(CONFIG_EARLY_PRINTK_USB) += early/
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obj-$(CONFIG_USB_ATM) += atm/
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obj-$(CONFIG_USB_SPEEDTOUCH) += atm/

‎drivers/usb/early/Makefile‎

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@@ -3,3 +3,4 @@
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#
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obj-$(CONFIG_EARLY_PRINTK_DBGP) += ehci-dbgp.o
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obj-$(CONFIG_EARLY_PRINTK_USB_XDBC) += xhci-dbc.o

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