[PATCH v7 16/28] Documentation: tracing: Add tracing remotes

[Vincent Donnefort <vdonnefort@google.com>]

Add documentation about the newly introduced tracing remotes framework.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index b4a429dc4f7a..d77ffb7e2d08 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -90,6 +90,17 @@ interactions.
    user_events
    uprobetracer
 
+Remote Tracing
+--------------
+
+This section covers the framework to read compatible ring-buffers, written by
+entities outside of the kernel (most likely firmware or hypervisor)
+
+.. toctree::
+   :maxdepth: 1
+
+   remotes
+
 Additional Resources
 --------------------
 
diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.rst
new file mode 100644
index 000000000000..e7fb3ee96c30
--- /dev/null
+++ b/Documentation/trace/remotes.rst
@@ -0,0 +1,59 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Tracing Remotes
+===============
+
+:Author: Vincent Donnefort <vdonnefort@google.com>
+
+Overview
+========
+A trace remote relies on ring-buffer remotes to read and control compatible
+tracing buffers, written by entity such as firmware or hypervisor.
+
+Once registered, a tracefs instance will appear for this remote in the Tracefs
+directory **remotes/**. This remote can be read and controlled using the same
+files as regular Tracefs instances such as **trace_pipe**, **tracing_on** or
+**trace**.
+
+Register a remote
+=================
+A remote must provide a set of callbacks `struct trace_remote_callbacks` whom
+description can be found below. Those callbacks allows Tracefs to enable and
+disable tracing and events, to load and unload a tracing buffer (a set of
+ring-buffers) and to swap a reader page with the head page, which enables
+consuming reading.
+
+.. kernel-doc:: include/linux/trace_remote.h
+
+Declare a remote event
+======================
+Macros are provided to ease the declaration of remote events, in a similar
+fashion to in-kernel events. A declaration must provide an ID, a description of
+the event arguments and how to print the event:
+
+.. code-block:: c
+
+	REMOTE_EVENT(foo, EVENT_FOO_ID,
+		RE_STRUCT(
+			re_field(u64, bar)
+		),
+		RE_PRINTK("bar=%lld", __entry->bar)
+	);
+
+Then those events must be declared in a C file with the following:
+
+.. code-block:: c
+
+	#define REMOTE_EVENT_INCLUDE_FILE foo_events.h
+	#include <trace/define_remote_events.h>
+
+This will provide a `struct remote_event remote_event_foo` that can be given to
+`trace_remote_register`.
+
+Simple ring-buffer
+==================
+A simple implementation for a ring-buffer writer can be found in
+kernel/trace/simple_ring_buffer.c.
+
+.. kernel-doc:: include/linux/simple_ring_buffer.h
-- 
2.51.0.618.g983fd99d29-goog