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

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Message-ID: <7c9a8dd4-7607-55a2-3d65-a445fa246667@roeck-us.net>
Date:   Sat, 30 Oct 2021 08:14:47 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sam Protsenko <semen.protsenko@...aro.org>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        linux-watchdog@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH 7/7] watchdog: s3c2410: Let kernel kick watchdog

On 10/30/21 7:29 AM, Sam Protsenko wrote:
> On Fri, 29 Oct 2021 at 03:30, Guenter Roeck <linux@...ck-us.net> 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@...aro.org>
>>> ---
>>>    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