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Commit bd566189 authored by Alexander Shishkin's avatar Alexander Shishkin
Browse files

stm class: Document the stm_source interface 



This patch adds a description of the stm_source device class, an
interface for the kernel code to send traces over STM devices.

Cc: linux-api@vger.kernel.org
Cc: Chunyan Zhang <zhang.chunyan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: default avatarAlexander Shishkin <alexander.shishkin@linux.intel.com>
parent a0ebf519

Documentation/trace/stm.txt

+24 −3
Original line number Diff line number Diff line
@@ -69,12 +69,33 @@ stm device's channel mmio region is 64 bytes and hardware page size is 
width==64, you should be able to mmap() one page on this file

descriptor and obtain direct access to an mmio region for 64 channels.



Examples of STM devices are Intel(R) Trace Hub [1] and Coresight STM

[2].



stm_source

==========



For kernel-based trace sources, there is "stm_source" device

class. Devices of this class can be connected and disconnected to/from

stm devices at runtime via a sysfs attribute.

stm devices at runtime via a sysfs attribute called "stm_source_link"

by writing the name of the desired stm device there, for example:



Examples of STM devices are Intel(R) Trace Hub [1] and Coresight STM

[2].

$ echo dummy_stm.0 > /sys/class/stm_source/console/stm_source_link



For examples on how to use stm_source interface in the kernel, refer

to stm_console or stm_heartbeat drivers.



stm_console

===========



One implementation of this interface also used in the example above is

the "stm_console" driver, which basically provides a one-way console

for kernel messages over an stm device.



To configure the master/channel pair that will be assigned to this

console in the STP stream, create a "console" policy entry (see the

beginning of this text on how to do that). When initialized, it will

consume one channel.



[1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf

[2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0444b/index.html