[PATCH v6 1/2] Documentation: add watchdog documentation

* [PATCH v6 1/2] Documentation: add watchdog documentation
@ 2019-10-24  6:03 Oleksij Rempel
  2019-10-24  6:03 ` [PATCH v6 2/2] doc: watchdog: add note about danger of autoping Oleksij Rempel
  2019-10-28 11:36 ` [PATCH v6 1/2] Documentation: add watchdog documentation Sascha Hauer
  0 siblings, 2 replies; 3+ messages in thread
From: Oleksij Rempel @ 2019-10-24  6:03 UTC (permalink / raw)
  To: barebox; +Cc: Oleksij Rempel

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 Documentation/user/user-manual.rst |  1 +
 Documentation/user/watchdog.rst    | 85 ++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 Documentation/user/watchdog.rst

diff --git a/Documentation/user/user-manual.rst b/Documentation/user/user-manual.rst
index f04981c3f0..41fdb8805c 100644
--- a/Documentation/user/user-manual.rst
+++ b/Documentation/user/user-manual.rst
@@ -34,6 +34,7 @@ Contents:
    state
    random
    debugging
+   watchdog
 
 * :ref:`search`
 * :ref:`genindex`
diff --git a/Documentation/user/watchdog.rst b/Documentation/user/watchdog.rst
new file mode 100644
index 0000000000..26e347d5f6
--- /dev/null
+++ b/Documentation/user/watchdog.rst
@@ -0,0 +1,85 @@
+Watchdog Support
+================
+
+Barebox Watchdog Functionality
+------------------------------
+
+In some cases we are not able to influence the hardware design anymore or while
+developing one needs to be able to feed the watchdog to disable it from within
+the bootloader. For these scenarios barebox provides the watchdog framework
+with the following functionality and at least ``CONFIG_WATCHDOG`` should be
+enabled.
+
+Polling
+~~~~~~~
+
+Watchdog polling/feeding allows to feed the watchdog and keep it running on one
+side and to not reset the system on the other side. It is needed on hardware
+with short-time watchdogs. For example the Atheros ar9331 watchdog has a
+maximal timeout of 7 seconds, so it may reset even on netboot.
+Or it can be used on systems where the watchdog is already running and can't be
+disabled, an example for that is the watchdog of the i.MX2 series.
+This functionally can be seen as a threat, since in error cases barebox will
+continue to feed the watchdog even if that is not desired. So, depending on
+your needs ``CONFIG_WATCHDOG_POLLER`` can be enabled or disabled at compile
+time. Even if barebox was built with watchdog polling support, it is not
+enabled by default. To start polling from command line run:
+
+.. code-block:: console
+
+  wdog0.autoping=1
+
+The poller interval is not configurable, but fixed at 500ms and the watchdog
+timeout is configured by default to the maximum of the supported values by
+hardware. To change the timeout used by the poller, run:
+
+.. code-block:: console
+
+  wdog0.timeout_cur=7
+
+To read the current watchdog's configuration, run:
+
+.. code-block:: console
+
+  devinfo wdog0
+
+The output may look as follows where ``timeout_cur`` and ``timeout_max`` are
+measured in seconds:
+
+.. code-block:: console
+
+  barebox@DPTechnics DPT-Module:/ devinfo wdog0
+  Parameters:
+    autoping: 1 (type: bool)
+    timeout_cur: 7 (type: uint32)
+    timeout_max: 10 (type: uint32)
+
+Use barebox' environment to persist these changes between reboots:
+
+.. code-block:: console
+
+  nv dev.wdog0.autoping=1
+  nv dev.wdog0.timeout_cur=7
+
+Boot Watchdog Timeout
+~~~~~~~~~~~~~~~~~~~~~
+
+With this functionality barebox may start a watchdog or update the timeout of
+an already-running one, just before kicking the boot image. It can be
+configured temporarily via
+
+.. code-block:: console
+
+  global boot.watchdog_timeout=10
+
+or persistently by
+
+.. code-block:: console
+
+  nv boot.watchdog_timeout=10
+
+where the used value again is measured in seconds.
+
+On a system with multiple watchdogs, the watchdog with the highest positive
+priority is the one affected by the ``boot.watchdog_timeout`` parameter.  If
+multiple watchdogs share the same priority, only one will be started.
-- 
2.23.0


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