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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: Alexander Shishkin <alexander.shishkin@linux.intel.com>
This commit is contained in:
Alexander Shishkin 2016-07-14 13:39:20 +03:00
parent a0ebf519b8
commit bd56618972
1 changed files with 25 additions and 4 deletions
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29
Documentation/trace/stm.txt
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@ -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.
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.
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 called "stm_source_link"
by writing the name of the desired stm device there, for example:
$ 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