xref: /linux/Documentation/watchdog/npcm_wdt.rst (revision 4e1b759c06721bc4e0fdfe5c179b58e7e20d3d13) 
1.. SPDX-License-Identifier: GPL-2.0
2
3=============
4NPCM Watchdog
5=============
6
7The NPCM watchdog driver can report reset-cause information on
8``nuvoton,npcm750-wdt`` and ``nuvoton,npcm845-wdt`` systems.
9
10Userspace can read the latched reset cause through
11``WDIOC_GETBOOTSTATUS``. When ``CONFIG_WATCHDOG_SYSFS`` is enabled, the
12same value is also visible through ``/sys/class/watchdog/watchdogN/bootstatus``.
13
14The mapping is fixed in the driver. It exposes the SoC reset indications
15through the generic watchdog bootstatus flags and is not configurable from
16Device Tree.
17
18.. list-table:: Reset-cause mapping
19   :header-rows: 1
20
21   * - Platform
22     - Reset indication
23     - Bootstatus flag
24     - Reported meaning
25   * - NPCM750 and NPCM845
26     - ``PORST``
27     - ``WDIOF_OVERHEAT``
28     - power-on reset
29   * - NPCM750 and NPCM845
30     - ``CORST``
31     - ``WDIOF_FANFAULT``
32     - core reset
33   * - NPCM750 and NPCM845
34     - ``SWR1RST``
35     - ``WDIOF_EXTERN1``
36     - software reset source 1
37   * - NPCM750 and NPCM845
38     - ``SWR2RST``
39     - ``WDIOF_EXTERN2``
40     - software reset source 2
41   * - NPCM750 and NPCM845
42     - ``SWR3RST``
43     - ``WDIOF_POWERUNDER``
44     - software reset source 3
45   * - NPCM750
46     - ``SWR4RST``
47     - ``WDIOF_POWEROVER``
48     - software reset source 4
49   * - NPCM845
50     - ``TIP reset`` (``INTCR2[25]``)
51     - ``WDIOF_POWEROVER``
52     - TIP reset
53
54``WDIOF_CARDRESET`` is reported only for the watchdog instance whose own
55reset-status bit is latched. On systems with three watchdog instances, this
56maps ``WD0RST``, ``WD1RST``, and ``WD2RST`` to ``watchdog0``, ``watchdog1``,
57and ``watchdog2`` respectively.
58
59The driver may report ``WDIOF_CARDRESET`` together with one or more of the
60reset-cause flags listed above.
61
62On NPCM750, the driver samples ``RESSR``. When reset bits are still latched,
63it clears them and stores the sampled value in ``SCRPAD2`` so later watchdog
64probes can report the same boot-time state.
65
66On NPCM845, the driver samples ``INTCR2``. When reset bits are still latched,
67it clears them and stores the sampled value in ``SCRPAD10`` so later watchdog
68probes can report the same boot-time state.
69
70The WPCM450 watchdog continues to operate without this reset-indication
71mapping.
72