Documentation/trace/coresight/coresight-config.rst

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======================================
CoreSight System Configuration Manager
======================================

    :Author:   Mike Leach <mike.leach@linaro.org>
    :Date:     October 2020

Introduction
============

The CoreSight System Configuration manager is an API that allows the
programming of the CoreSight system with pre-defined configurations that
can then be easily enabled from sysfs or perf.

Many CoreSight components can be programmed in complex ways - especially ETMs.
In addition, components can interact across the CoreSight system, often via
the cross trigger components such as CTI and CTM. These system settings can
be defined and enabled as named configurations.


Basic Concepts
==============

This section introduces the basic concepts of a CoreSight system configuration.


Features
--------

A feature is a named set of programming for a CoreSight device. The programming
is device dependent, and can be defined in terms of absolute register values,
resource usage and parameter values.

The feature is defined using a descriptor. This descriptor is used to load onto
a matching device, either when the feature is loaded into the system, or when the
CoreSight device is registered with the configuration manager.

The load process involves interpreting the descriptor into a set of register
accesses in the driver - the resource usage and parameter descriptions
translated into appropriate register accesses. This interpretation makes it easy
and efficient for the feature to be programmed onto the device when required.

The feature will not be active on the device until the feature is enabled, and
the device itself is enabled. When the device is enabled then enabled features
will be programmed into the device hardware.

A feature is enabled as part of a configuration being enabled on the system.


Parameter Value
~~~~~~~~~~~~~~~

A parameter value is a named value that may be set by the user prior to the
feature being enabled that can adjust the behaviour of the operation programmed
by the feature.

For example, this could be a count value in a programmed operation that repeats
at a given rate. When the feature is enabled then the current value of the
parameter is used in programming the device.

The feature descriptor defines a default value for a parameter, which is used
if the user does not supply a new value.

Users can update parameter values using the configfs API for the CoreSight
system - which is described below.

The current value of the parameter is loaded into the device when the feature
is enabled on that device.

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Implementation Notes