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

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Date:   Thu, 28 Oct 2021 17:30:54 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 7/7] watchdog: s3c2410: Let kernel kick watchdog

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.

Guenter

>   	ret = watchdog_register_device(&wdt->wdt_device);
>   	if (ret)
>   		goto err_cpufreq;
> @@ -740,17 +755,6 @@ static int s3c2410wdt_probe(struct platform_device *pdev)
>   	if (ret < 0)
>   		goto err_unregister;
>   
> -	if (tmr_atboot && started == 0) {
> -		dev_info(dev, "starting watchdog timer\n");
> -		s3c2410wdt_start(&wdt->wdt_device);
> -	} else if (!tmr_atboot) {
> -		/* if we're not enabling the watchdog, then ensure it is
> -		 * disabled if it has been left running from the bootloader
> -		 * or other source */
> -
> -		s3c2410wdt_stop(&wdt->wdt_device);
> -	}
> -
>   	platform_set_drvdata(pdev, wdt);
>   
>   	/* print out a statement of readiness */
>