linux-kernel - Re: [PATCH v3 1/1] drivers: watchdog: stm32_iwdg: set WDOG_HW

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Date:   Fri, 22 Nov 2019 10:15:13 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christophe Roullier <christophe.roullier@...com>
Cc:     wim@...ux-watchdog.org, mcoquelin.stm32@...il.com,
        alexandre.torgue@...com, linux-watchdog@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/1] drivers: watchdog: stm32_iwdg: set
 WDOG_HW_RUNNING at probe

On Fri, Nov 22, 2019 at 02:22:46PM +0100, Christophe Roullier wrote:
> If the watchdog hardware is already enabled during the boot process,
> when the Linux watchdog driver loads, it should start/reset the watchdog
> and tell the watchdog framework. As a result, ping can be generated from
> the watchdog framework (if CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED is set),
> until the userspace watchdog daemon takes over control
> 
> Fixes:4332d113c66a ("watchdog: Add STM32 IWDG driver")
> 
> Signed-off-by: Christophe Roullier <christophe.roullier@...com>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
> Changes since v2:
> According to Guenter
> removed intermediate variable
> 
> I've tested some config and it is working as expected:
> Watchdog enable in Uboot + HANDLE_BOOT_ENABLE is not set + daemon watchdog in userland ON ==> No reset IWDG2
> Watchdog enable in Uboot + HANDLE_BOOT_ENABLE is not set ==> Reset IWDG2
> Watchdog enable in Uboot + HANDLE_BOOT_ENABLE=y ==> No reset IWDG2
> Watchdog enable in Uboot + HANDLE_BOOT_ENABLE=y + daemon watchdog in userland ON puis OFF ==> Reset IWDG2
> Watchdog disable in Uboot + HANDLE_BOOT_ENABLE is not set ==> No reset IWDG2
> Watchdog disable in Uboot + HANDLE_BOOT_ENABLE=y ==> No reset IWDG2
> Watchdog disable in Uboot + HANDLE_BOOT_ENABLE=y + daemon watchdog in userland ON ==> No reset IWDG2
> Watchdog disable in Uboot + HANDLE_BOOT_ENABLE=y + daemon watchdog in userland ON puis OFF ==> Reset IWDG2
> 
> Thanks,
> Christophe
> 
>  drivers/watchdog/stm32_iwdg.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/watchdog/stm32_iwdg.c b/drivers/watchdog/stm32_iwdg.c
> index a3a329011a06..25188d6bbe15 100644
> --- a/drivers/watchdog/stm32_iwdg.c
> +++ b/drivers/watchdog/stm32_iwdg.c
> @@ -262,6 +262,24 @@ static int stm32_iwdg_probe(struct platform_device *pdev)
>  	watchdog_set_nowayout(wdd, WATCHDOG_NOWAYOUT);
>  	watchdog_init_timeout(wdd, 0, dev);
>  
> +	/*
> +	 * In case of CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED is set
> +	 * (Means U-Boot/bootloaders leaves the watchdog running)
> +	 * When we get here we should make a decision to prevent
> +	 * any side effects before user space daemon will take care of it.
> +	 * The best option, taking into consideration that there is no
> +	 * way to read values back from hardware, is to enforce watchdog
> +	 * being run with deterministic values.
> +	 */
> +	if (IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED)) {
> +		ret = stm32_iwdg_start(wdd);
> +		if (ret)
> +			return ret;
> +
> +		/* Make sure the watchdog is serviced */
> +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> +	}
> +
>  	ret = devm_watchdog_register_device(dev, wdd);
>  	if (ret)
>  		return ret;
> -- 
> 2.17.1
>