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

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Message-ID: <2bb28691-def0-4365-98e0-7f53d4d19966@roeck-us.net>
Date: Mon, 19 May 2025 18:13:12 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Julius Werner <jwerner@...omium.org>
Cc: Antonio Borneo <antonio.borneo@...s.st.com>,
 Evan Benn <evanbenn@...omium.org>, Wim Van Sebroeck
 <wim@...ux-watchdog.org>, linux-watchdog@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH] watchdog: arm_smc_wdt: get wdt status through
 SMCWD_GET_TIMELEFT

On 5/19/25 17:12, Julius Werner wrote:
> I don't really know about the issue Guenter mentioned, but otherwise,
> from the driver's side this looks good to me.
> 

It should just be
	set_bit(WDOG_HW_RUNNING, &wdd->status);

There should be no dependency on CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED.

Guenter
	
> Reviewed-by: Julius Werner <jwerner@...omium.org>
> 
> On Mon, May 19, 2025 at 10:58 AM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 5/19/25 10:00, Antonio Borneo wrote:
>>> 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].
>>>
>>> If CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED is set, 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 | 18 +++++++++++++++---
>>>    1 file changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/watchdog/arm_smc_wdt.c b/drivers/watchdog/arm_smc_wdt.c
>>> index 8f3d0c3a005fb..f1268f43327ea 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 +133,20 @@ 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:
>>> +             if (IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED))
>>> +                     set_bit(WDOG_HW_RUNNING, &wdd->status);
>>
>> This is the wrong use of this configuration option. It is only needed
>> in a driver if the watchdog status can not be read from hardware.
>> That is not the case here. Worse, using it in a driver like this
>> overrides the watchdog core module parameter "handle_boot_enabled".
>>
>> Guenter
>>
>>> +             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
>>