path: root/Documentation
diff options
Diffstat (limited to 'Documentation')
3 files changed, 93 insertions, 1 deletions
diff --git a/Documentation/boards/efi.rst b/Documentation/boards/efi.rst
index 2178c9ab4..f04b1d323 100644
--- a/Documentation/boards/efi.rst
+++ b/Documentation/boards/efi.rst
@@ -350,7 +350,7 @@
Current linux kernel (v5.0) will execute ExitBootServices() during the early
boot stage and thus will automatically disable the (U)EFI watchdog. Since it is
-a proper behavior according to the (U)EFI specification, it is impossible to
+the proper behavior according to the (U)EFI specification, it is impossible to
protect full boot chain by using this watchdog only. It is recommended to use
an alternative hardware watchdog, preferably started before the bootloader. If (U)EFI
firmware lacks this feature, the bootloader should be able to start an alternative
diff --git a/Documentation/user/user-manual.rst b/Documentation/user/user-manual.rst
index f04981c3f..41fdb8805 100644
--- a/Documentation/user/user-manual.rst
+++ b/Documentation/user/user-manual.rst
@@ -34,6 +34,7 @@ Contents:
+ watchdog
* :ref:`search`
* :ref:`genindex`
diff --git a/Documentation/user/watchdog.rst b/Documentation/user/watchdog.rst
new file mode 100644
index 000000000..02bd576a8
--- /dev/null
+++ b/Documentation/user/watchdog.rst
@@ -0,0 +1,91 @@
+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
+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
+**NOTE** Using this feature might have the effect that the watchdog is
+effectively disabled. In case barebox is stuck in a loop that includes feeding
+the watchdog, then the watchdog will never trigger. Only use this feature
+during development or when a bad watchdog design (Short watchdog timeout
+enabled as boot default) doesn't give you another choice.
+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.