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

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Message-ID: <CAODwPW-gEOotp8KGhzk3E11PqF9xdan8dOwxe_SW4txh+uQp=w@mail.gmail.com>
Date: Mon, 19 May 2025 17:12:20 -0700
From: Julius Werner <jwerner@...omium.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Antonio Borneo <antonio.borneo@...s.st.com>, Julius Werner <jwerner@...omium.org>, 
	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

I don't really know about the issue Guenter mentioned, but otherwise,
from the driver's side this looks good to me.

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
>