linux-kernel - [PATCH v2] watchdog: arm_smc_wdt: get wdt status through SMCWD_GET

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Message-ID: <20250520085952.210723-1-antonio.borneo@foss.st.com>
Date: Tue, 20 May 2025 10:59:52 +0200
From: Antonio Borneo <antonio.borneo@...s.st.com>
To: Julius Werner <jwerner@...omium.org>, Evan Benn <evanbenn@...omium.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck
	<linux@...ck-us.net>, <linux-watchdog@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC: Antonio Borneo <antonio.borneo@...s.st.com>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: [PATCH v2] watchdog: arm_smc_wdt: get wdt status through SMCWD_GET_TIMELEFT

The optional SMCWD_GET_TIMELEFT command can be used to detect if
the watchdog has already been started.
See the implementation in OP-TEE secure OS [1].

At probe time, check if the watchdog is already started and then
set WDOG_HW_RUNNING in the watchdog status. This will cause the
watchdog framework to ping the watchdog until a userspace watchdog
daemon takes over the control.

Link: https://github.com/OP-TEE/optee_os/commit/a7f2d4bd8632 [1]

Signed-off-by: Antonio Borneo <antonio.borneo@...s.st.com>
---
 drivers/watchdog/arm_smc_wdt.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/arm_smc_wdt.c b/drivers/watchdog/arm_smc_wdt.c
index 8f3d0c3a005fb..bbba23ace7b85 100644
--- a/drivers/watchdog/arm_smc_wdt.c
+++ b/drivers/watchdog/arm_smc_wdt.c
@@ -46,6 +46,8 @@ static int smcwd_call(struct watchdog_device *wdd, enum smcwd_call call,
 		return -ENODEV;
 	if (res->a0 == PSCI_RET_INVALID_PARAMS)
 		return -EINVAL;
+	if (res->a0 == PSCI_RET_DISABLED)
+		return -ENODATA;
 	if (res->a0 != PSCI_RET_SUCCESS)
 		return -EIO;
 	return 0;
@@ -131,10 +133,19 @@ static int smcwd_probe(struct platform_device *pdev)
 
 	wdd->info = &smcwd_info;
 	/* get_timeleft is optional */
-	if (smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL))
-		wdd->ops = &smcwd_ops;
-	else
+	err = smcwd_call(wdd, SMCWD_GET_TIMELEFT, 0, NULL);
+	switch (err) {
+	case 0:
+		set_bit(WDOG_HW_RUNNING, &wdd->status);
+		fallthrough;
+	case -ENODATA:
 		wdd->ops = &smcwd_timeleft_ops;
+		break;
+	default:
+		wdd->ops = &smcwd_ops;
+		break;
+	}
+
 	wdd->timeout = res.a2;
 	wdd->max_timeout = res.a2;
 	wdd->min_timeout = res.a1;

base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21
-- 
2.34.1