[RFC PATCH v2 0/3] Integration of trace events with System Trace IP blocks

From: Chunyan Zhang
Date: Tue Jun 16 2015 - 03:06:45 EST

IP blocks allowing a variety of trace sources to log debugging
information to a pre-defined area have been introduced on a couple of
architecture [1][2]. These system trace blocks (also known as STM)
typically follow the MIPI STPv2 protocol [3] and provide a system wide
logging facility to any device, running a kernel or not, with access
to the block's log entry port(s). Since each trace message has a
timestamp is it possible to correlate events happening in the entire
system rather than being confined to the logging facility of a single

This patch is using a very simple "stm_source" introduced in [2] to
duplicate the output of the trace event subsystem to an STM, in this
case coresight STM. That way logging information generated by the
trace event subsystem and gathered in the coresight sink can be used
in conjunction with trace data from other board components, also
collected in the same trace sink. This example is using coresight but
the same would apply to any architecture wishing to do the same.

The goal of this RFC is to solicit comments on the method used to
connect trace event logging with STMs (using the generic STM API)
rather than function "stm_ftrace_write()" itself, which was provided
for completeness of the proof of concept only.

I'm eager to see your comments on this, and if you have some good
ideas that can slow down the overhead, please let me know. Any
questions are also welcome.


[1]. https://lkml.org/lkml/2015/2/4/729
[2]. http://comments.gmane.org/gmane.linux.kernel/1914526
[3]. http://mipi.org/specifications/debug#STP

Changes from RFC v1:
- Marked module init/exit functions with __init/__exit key word
according to the comments from Paul Bolle

Chunyan Zhang (2):
Trace log handler for logging into STM blocks
Introduce trace log output function for STM

Mathieu Poirier (1):
STM trace event: Adding generic buffer interface driver

drivers/stm/Kconfig | 11 +++++
drivers/stm/Makefile | 2 +
drivers/stm/stm_trace_event.c | 46 +++++++++++++++++++
include/linux/ftrace_event.h | 15 +++++++
include/trace/ftrace.h | 47 +++++++++++++++++++
kernel/trace/Makefile | 1 +
kernel/trace/trace_output_stm.c | 99 +++++++++++++++++++++++++++++++++++++++++
7 files changed, 221 insertions(+)
create mode 100644 drivers/stm/stm_trace_event.c
create mode 100644 kernel/trace/trace_output_stm.c


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