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Add documentation describing how the NPCM watchdog driver reports reset causes through bootstatus on NPCM750 and NPCM845 systems. Document the reset flag mapping, the watchdog instance mapping for WDIOF_CARDRESET, and the NPCM750/NPCM845 latch handling. Also mention sysfs bootstatus reporting when watchdog sysfs support is enabled. Signed-off-by: Tomer Maimon <tmaimon77@gmail.com> Link: https://lore.kernel.org/r/20260706144828.3517631-3-tmaimon77@gmail.com Signed-off-by: Guenter Roeck <linux@roeck-us.net>
72 lines
2.2 KiB
ReStructuredText
72 lines
2.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=============
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NPCM Watchdog
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=============
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The NPCM watchdog driver can report reset-cause information on
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``nuvoton,npcm750-wdt`` and ``nuvoton,npcm845-wdt`` systems.
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Userspace can read the latched reset cause through
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``WDIOC_GETBOOTSTATUS``. When ``CONFIG_WATCHDOG_SYSFS`` is enabled, the
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same value is also visible through ``/sys/class/watchdog/watchdogN/bootstatus``.
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The mapping is fixed in the driver. It exposes the SoC reset indications
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through the generic watchdog bootstatus flags and is not configurable from
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Device Tree.
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.. list-table:: Reset-cause mapping
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:header-rows: 1
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* - Platform
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- Reset indication
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- Bootstatus flag
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- Reported meaning
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* - NPCM750 and NPCM845
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- ``PORST``
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- ``WDIOF_OVERHEAT``
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- power-on reset
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* - NPCM750 and NPCM845
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- ``CORST``
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- ``WDIOF_FANFAULT``
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- core reset
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* - NPCM750 and NPCM845
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- ``SWR1RST``
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- ``WDIOF_EXTERN1``
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- software reset source 1
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* - NPCM750 and NPCM845
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- ``SWR2RST``
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- ``WDIOF_EXTERN2``
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- software reset source 2
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* - NPCM750 and NPCM845
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- ``SWR3RST``
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- ``WDIOF_POWERUNDER``
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- software reset source 3
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* - NPCM750
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- ``SWR4RST``
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- ``WDIOF_POWEROVER``
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- software reset source 4
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* - NPCM845
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- ``TIP reset`` (``INTCR2[25]``)
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- ``WDIOF_POWEROVER``
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- TIP reset
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``WDIOF_CARDRESET`` is reported only for the watchdog instance whose own
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reset-status bit is latched. On systems with three watchdog instances, this
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maps ``WD0RST``, ``WD1RST``, and ``WD2RST`` to ``watchdog0``, ``watchdog1``,
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and ``watchdog2`` respectively.
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The driver may report ``WDIOF_CARDRESET`` together with one or more of the
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reset-cause flags listed above.
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On NPCM750, the driver samples ``RESSR``. When reset bits are still latched,
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it clears them and stores the sampled value in ``SCRPAD2`` so later watchdog
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probes can report the same boot-time state.
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On NPCM845, the driver samples ``INTCR2``. When reset bits are still latched,
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it clears them and stores the sampled value in ``SCRPAD10`` so later watchdog
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probes can report the same boot-time state.
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The WPCM450 watchdog continues to operate without this reset-indication
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mapping.
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