2 files changed, 27 insertions, 2 deletions

diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt
index 674c5663d346..58ea64a96165 100644
--- a/Documentation/dynamic-debug-howto.txt
+++ b/Documentation/dynamic-debug-howto.txt
@@ -24,7 +24,7 @@ Dynamic debug has even more useful features:
    read to display the complete list of known debug statements, to help guide you
 
 Controlling dynamic debug Behaviour
-===============================
+===================================
 
 The behaviour of pr_debug()/dev_debug()s are controlled via writing to a
 control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
@@ -212,6 +212,26 @@ Note the regexp ^[-+=][scp]+$ matches a flags specification.
 Note also that there is no convenient syntax to remove all
 the flags at once, you need to use "-psc".
 
+
+Debug messages during boot process
+==================================
+
+To be able to activate debug messages during the boot process,
+even before userspace and debugfs exists, use the boot parameter:
+ddebug_query="QUERY"
+
+QUERY follows the syntax described above, but must not exceed 1023
+characters. The enablement of debug messages is done as an arch_initcall.
+Thus you can enable debug messages in all code processed after this
+arch_initcall via this boot parameter.
+On an x86 system for example ACPI enablement is a subsys_initcall and
+ddebug_query="file ec.c +p"
+will show early Embedded Controller transactions during ACPI setup if
+your machine (typically a laptop) has an Embedded Controller.
+PCI (or other devices) initialization also is a hot candidate for using
+this boot parameter for debugging purposes.
+
+
 Examples
 ========
 
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 8dd7248508a9..3d854c9ae53a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -43,10 +43,11 @@ parameter is applicable:
         AVR32   AVR32 architecture is enabled.
         AX25    Appropriate AX.25 support is enabled.
         BLACKFIN Blackfin architecture is enabled.
-        DRM     Direct Rendering Management support is enabled.
         EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
         EFI     EFI Partitioning (GPT) is enabled
         EIDE    EIDE/ATAPI support is enabled.
+        DRM     Direct Rendering Management support is enabled.
+        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
         FB      The frame buffer device is enabled.
         GCOV    GCOV profiling is enabled.
         HW      Appropriate hardware is enabled.
@@ -570,6 +571,10 @@ and is between 256 and 4096 characters. It is defined in the file
                         Format: <port#>,<type>
                         See also Documentation/input/joystick-parport.txt
 
+        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
+                        time. See Documentation/dynamic-debug-howto.txt for
+                        details.
+
         debug           [KNL] Enable kernel debugging (events log level).
 
         debug_locks_verbose=