Re: [PATCH 7/7] watchdog: s3c2410: Let kernel kick watchdog

[Guenter Roeck]

On 10/30/21 7:29 AM, Sam Protsenko wrote:
> On Fri, 29 Oct 2021 at 03:30, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 10/28/21 11:35 AM, Sam Protsenko wrote:
> > > When "tmr_atboot" module param is set, the watchdog is started in
> > > driver's probe. In that case, also set WDOG_HW_RUNNING bit to let
> > > watchdog core driver know it's running. This way wathcdog core can kick
> > > the watchdog for us (if CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED option is
> > > enabled), until user space takes control.
> > >
> > > Signed-off-by: Sam Protsenko <semen.protsenko@xxxxxxxxxx>
> > > ---
> > >    drivers/watchdog/s3c2410_wdt.c | 26 +++++++++++++++-----------
> > >    1 file changed, 15 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> > > index ca082b1226e3..9af014ff1468 100644
> > > --- a/drivers/watchdog/s3c2410_wdt.c
> > > +++ b/drivers/watchdog/s3c2410_wdt.c
> > > @@ -732,6 +732,21 @@ static int s3c2410wdt_probe(struct platform_device *pdev)
> > >        wdt->wdt_device.bootstatus = s3c2410wdt_get_bootstatus(wdt);
> > >        wdt->wdt_device.parent = dev;
> > >
> > > +     /*
> > > +      * If "tmr_atboot" param is non-zero, start the watchdog right now. Also
> > > +      * set WDOG_HW_RUNNING bit, so that watchdog core can kick the watchdog.
> > > +      *
> > > +      * If we're not enabling the watchdog, then ensure it is disabled if it
> > > +      * has been left running from the bootloader or other source.
> > > +      */
> > > +     if (tmr_atboot && started == 0) {
> > > +             dev_info(dev, "starting watchdog timer\n");
> > > +             s3c2410wdt_start(&wdt->wdt_device);
> > > +             set_bit(WDOG_HW_RUNNING, &wdt->wdt_device.status);
> > > +     } else if (!tmr_atboot) {
> > > +             s3c2410wdt_stop(&wdt->wdt_device);
> > > +     }
> > > +
> >
> > This doesn't cover the case where the watchdog is already enabled by the BIOS.
> > In that case, WDOG_HW_RUNNING won't be set, and the watchdog will time out
> > if the userspace handler is not loaded fast enough. The code should consistently
> > set WDOG_HW_RUNNING if the watchdog is running.
>
> As I understand, in the case when bootloader started the watchdog, the
> driver just stops it. You can see it in the code you replied to.
>
>      } else if (!tmr_atboot) {
>              s3c2410wdt_stop(&wdt->wdt_device);
>
> In other words, having "tmr_atboot" module param makes it irrelevant
> whether bootloader enabled WDT or no.

Sure, but I am concerned about "if (tmr_atboot && started)", which doesn't
set WDOG_HW_RUNNING with your current code, and I was looking for something
like

	if (tmr_atboot) {
		if (!started) {
			dev_info(dev, "starting watchdog timer\n");
			s3c2410wdt_start(&wdt->wdt_device);
		}
		set_bit(WDOG_HW_RUNNING, &wdt->wdt_device.status);
	} else {
		s3c2410wdt_stop(&wdt->wdt_device);
	}

Guenter