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
Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20250520085952.210723-1-antonio.borneo@foss.st.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

diff --git a/drivers/watchdog/arm_smc_wdt.c b/drivers/watchdog/arm_smc_wdt.c
index 8f3d0c3a005fbfa0580e768a13e5d931e3adad03..bbba23ace7b859d3cbcda9356042afb08505b164 100644 (file)
--- 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;