linux-kernel - Re: [PATCH v2 1/1] drivers: watchdog: stm32_iwdg: set WDOG_HW

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Message-ID: <ffa20f2f-1ca2-9d8f-6594-33b906cbb74a@roeck-us.net>
Date:   Fri, 22 Nov 2019 02:45:49 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Christophe Roullier <christophe.roullier@...com>,
        wim@...ux-watchdog.org, mcoquelin.stm32@...il.com,
        alexandre.torgue@...com
Cc:     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 v2 1/1] drivers: watchdog: stm32_iwdg: set WDOG_HW_RUNNING
 at probe

On 11/22/19 12:24 AM, 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>
> ---
> Changes since v1:
> According to Guenter
> I follow the guidance from intel-mid_wdt.c
> and I added test to check if CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED is set
> because we need to be flexible (depends on customer config, but watchdog
> not always start by bootloader (Uboot, ..))
> 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 | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/watchdog/stm32_iwdg.c b/drivers/watchdog/stm32_iwdg.c
> index a3a329011a06..7f454a6e17ba 100644
> --- a/drivers/watchdog/stm32_iwdg.c
> +++ b/drivers/watchdog/stm32_iwdg.c
> @@ -50,6 +50,9 @@
>   #define TIMEOUT_US	100000
>   #define SLEEP_US	1000
>   
> +static bool handle_boot_enabled =
> +	IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);
> +
>   struct stm32_iwdg_data {
>   	bool has_pclk;
>   	u32 max_prescaler;
> @@ -262,6 +265,24 @@ 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 (handle_boot_enabled) {

You don't need that variable. Just use
	if (IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED)) {
directly.

> +		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;
>