doc: zbus: Runtime observers pool

Add documentation of the runtime observers pool.

Signed-off-by: Rodrigo Peixoto <rodrigopex@gmail.com>

doc/services/zbus/index.rst

@@ -848,29 +848,36 @@ The following code has the exact behavior of the code in :ref:`reading from a ch
 Runtime observer registration
 -----------------------------
 
-It is possible to add observers to channels at runtime if
-:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS` is enabled. In addition to the channel and observer
-references, :c:func:`zbus_chan_add_obs` also requires a :c:struct:`zbus_observer_node` to link the two
-together, which must remain valid in memory for the duration that the observer is attached to the
-channel. The simplest way to achieve this is to make the structure ``static``.
+It is possible to add observers to channels in runtime. Set the
+:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS` to enable the feature. This feature uses the heap to
+allocate the nodes dynamically, a memory slab to allocate the nodes statically, or user-provided
+nodes. It depends on the :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC`, which can be
+:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_DYNAMIC`,
+:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_STATIC`, and
+:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_NONE`. The dynamic is the default. When
+:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_STATIC` is enabled, you need to set the
+number of runtime observers you are going to use by setting the
+:kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_POOL_SIZE` configuration. The following example
+illustrates the runtime registration usage.
 
 .. code-block:: c
 
     ZBUS_LISTENER_DEFINE(my_listener, callback);
     // ...
     void thread_entry(void) {
-            static struct zbus_observer_node obs_node;
             // ...
             /* Adding the observer to channel chan1 */
-            zbus_chan_add_obs(&chan1, &my_listener, &obs_node, K_NO_WAIT);
+            zbus_chan_add_obs(&chan1, &my_listener, K_NO_WAIT);
             /* Removing the observer from channel chan1 */
             zbus_chan_rm_obs(&chan1, &my_listener, K_NO_WAIT);
 
+
 .. warning::
 
-  The :c:struct:`zbus_observer_node` can only be re-used in :c:func:`zbus_chan_add_obs` after removing
+  The :c:struct:`zbus_observer_node` can only be re-used in :c:func:`zbus_chan_add_obs_with_node` after removing
   the channel observer it was first associated with through :c:func:`zbus_chan_rm_obs`.
 
+
 Samples
 *******
 
@@ -936,7 +943,15 @@ Related configuration options:
   a pool for the message subscriber for a set of channels;
 * :kconfig:option:`CONFIG_ZBUS_MSG_SUBSCRIBER_NET_BUF_STATIC_DATA_SIZE` the biggest message of zbus
   channels to be transported into a message buffer;
-* :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS` enables the runtime observer registration.
+* :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS` enables the runtime observer registration;
+* :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_DYNAMIC` allocate the runtime observers
+  dynamically using the heap;
+* :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_STATIC` allocate the runtime observers
+  statically using a memory slab;
+* :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_POOL_SIZE` the amount of enabled runtime
+  observers to statically allocate.
+* :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_NONE` use user-provided runtime
+  observers nodes;
 
 API Reference
 *************