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Mon, 22 Jun 2026 01:31:12 -0700 (PDT) From: Tomer Maimon To: andrew@codeconstruct.com.au, wim@linux-watchdog.org, linux@roeck-us.net, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org Cc: openbmc@lists.ozlabs.org, linux-watchdog@vger.kernel.org, linux-doc@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, avifishman70@gmail.com, tmaimon77@gmail.com, tali.perry1@gmail.com, venture@google.com, yuenn@google.com, benjaminfair@google.com, corbet@lwn.net, skhan@linuxfoundation.org, joel@jms.id.au Subject: [PATCH v2 2/3] docs: watchdog: npcm: Add reset status description Date: Mon, 22 Jun 2026 11:30:45 +0300 Message-Id: <20260622083046.3189603-3-tmaimon77@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260622083046.3189603-1-tmaimon77@gmail.com> References: <20260622083046.3189603-1-tmaimon77@gmail.com> Precedence: bulk X-Mailing-List: linux-watchdog@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- Documentation/watchdog/index.rst | 1 + Documentation/watchdog/npcm_wdt.rst | 70 +++++++++++++++++++++++++++++ 2 files changed, 71 insertions(+) create mode 100644 Documentation/watchdog/npcm_wdt.rst diff --git a/Documentation/watchdog/index.rst b/Documentation/watchdog/index.rst index 1cea24681e6b..ef29e861e837 100644 --- a/Documentation/watchdog/index.rst +++ b/Documentation/watchdog/index.rst @@ -9,6 +9,7 @@ Watchdog Support hpwdt mlx-wdt + npcm_wdt pcwd-watchdog watchdog-api watchdog-kernel-api diff --git a/Documentation/watchdog/npcm_wdt.rst b/Documentation/watchdog/npcm_wdt.rst new file mode 100644 index 000000000000..48f0c7920c11 --- /dev/null +++ b/Documentation/watchdog/npcm_wdt.rst @@ -0,0 +1,70 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +NPCM Watchdog +============= + +The NPCM watchdog driver can report reset-cause information on +``nuvoton,npcm750-wdt`` and ``nuvoton,npcm845-wdt`` systems. + +Userspace can read the latched reset cause through +``WDIOC_GETBOOTSTATUS``. When ``CONFIG_WATCHDOG_SYSFS`` is enabled, the +same value is also visible through ``/sys/class/watchdog/watchdogN/bootstatus``. + +The mapping is fixed in the driver. It exposes the SoC reset indications +through the generic watchdog bootstatus flags and is not configurable from +Device Tree. + +.. list-table:: Reset-cause mapping + :header-rows: 1 + + * - Platform + - Reset indication + - Bootstatus flag + - Reported meaning + * - NPCM750 and NPCM845 + - ``PORST`` + - ``WDIOF_OVERHEAT`` + - power-on reset + * - NPCM750 and NPCM845 + - ``CORST`` + - ``WDIOF_FANFAULT`` + - core reset + * - NPCM750 and NPCM845 + - ``SWR1RST`` + - ``WDIOF_EXTERN1`` + - software reset source 1 + * - NPCM750 and NPCM845 + - ``SWR2RST`` + - ``WDIOF_EXTERN2`` + - software reset source 2 + * - NPCM750 and NPCM845 + - ``SWR3RST`` + - ``WDIOF_POWERUNDER`` + - software reset source 3 + * - NPCM750 + - ``SWR4RST`` + - ``WDIOF_POWEROVER`` + - software reset source 4 + * - NPCM845 + - ``TIP reset`` (``INTCR2[25]``) + - ``WDIOF_POWEROVER`` + - TIP reset + +``WDIOF_CARDRESET`` is reported only for the watchdog instance whose own +reset-status bit is latched. On systems with three watchdog instances, this +maps ``WD0RST``, ``WD1RST``, and ``WD2RST`` to ``watchdog0``, ``watchdog1``, +and ``watchdog2`` respectively. + +The driver may report ``WDIOF_CARDRESET`` together with one or more of the +reset-cause flags listed above. + +On NPCM750, the driver samples ``RESSR`` and clears the latched reset bits +after reading them. + +On NPCM845, the driver samples ``INTCR2``. When reset bits are still latched, +it clears them and stores the sampled value in ``SCRPAD10`` so later watchdog +probes can report the same boot-time state. + +The WPCM450 watchdog continues to operate without this reset-indication +mapping. -- 2.34.1