tracelevel module: Prioritize trace events

This module lets subsystem authors prioritize ftrace events
by calling tracelevel_register(...). High priority traces
will be automatically enabled on boot. See tracelevel.h
for more details

Original-Change-Id: If03699e96c598bdcf93b9a9f73918ce7b0c750cb
Reviewed-on: http://git-master/r/40290
Reviewed-by: Alon Farchy <afarchy@nvidia.com>
Tested-by: Alon Farchy <afarchy@nvidia.com>
Reviewed-by: Daniel Willemsen <dwillemsen@nvidia.com>
Tested-by: Daniel Solomon <daniels@nvidia.com>
Tested-by: Simone Willett <swillett@nvidia.com>

Rebase-Id: R49f59f81d61907f66fdf892130a1b4dc6575d40e

1 files changed, 42 insertions, 0 deletions

diff --git a/Documentation/trace/tracelevel.txt b/Documentation/trace/tracelevel.txt
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+			 Tracelevel
+
+		Documentation by Alon Farchy
+
+1. Overview
+===========
+
+Tracelevel allows subsystem authors to add trace priorities to
+their tracing events. High priority traces will be enabled
+automatically at boot time.
+
+This module is configured with CONFIG_TRACELEVEL.
+
+2. Usage
+=========
+
+To give an event a priority, use the function tracelevel_register
+at any time.
+
+	tracelevel_register(my_event, level);
+
+my_event corresponds directly to the event name as defined in the
+event header file. Available levels are:
+
+	TRACELEVEL_ERR 3
+	TRACELEVEL_WARN 2
+	TRACELEVEL_INFO 1
+	TRACELEVEL_DEBUG 0
+
+Any event registered at boot time as TRACELEVEL_ERR will be enabled
+by default. The header also exposes the function tracelevel_set_level
+to change the trace level at runtime. Any trace event registered with the
+specified level or higher will be enabled with this call.
+
+A userspace handle to tracelevel_set_level is available via the module
+parameter 'level'. For example,
+
+	echo 1 > /sys/module/tracelevel/parameters/level
+
+Is logically equivalent to:
+
+	tracelevel_set_level(TRACELEVEL_INFO);