Re: [PATCH v2 2/4] watchdog: implement generic support for .running device parameter

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi Ahmad,

On Mon, Nov 04, 2019 at 11:14:05PM +0100, Ahmad Fatoum wrote:
> Linux watchdog have an optional WDOG_HW_RUNNING bit that is used in
> conjunction with CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED to automatically
> ping running watchdogs until userspace takes over.
> 
> So far, when we ported Linux drivers, we dropped this detection, but it
> would be useful to have this information in barebox as well:
> 
> The American Megatrends BIOS I am using allows configuring the hardware
> watchdog from the BIOS. barebox enables the WDT as well, so in normal
> operation we would never notice if after a BIOS update, the watchdog is
> no longer enabled. If we maintain a running parameter on watchdog
> devices, board code can be written to check whether the watchdog device
> is indeed running.

To write such code I would prefer to have a function which returns the
running status rather than playing with getenv(). Additionally there is
a function missing in the watchdog code which returns a watchdog by its
name. This can be a future excercise, no need to do it in this patch.

> @@ -45,7 +47,18 @@ int watchdog_set_timeout(struct watchdog *wd, unsigned timeout)
>  
>  	pr_debug("setting timeout on %s to %ds\n", watchdog_name(wd), timeout);
>  
> -	return wd->set_timeout(wd, timeout);
> +	ret = wd->set_timeout(wd, timeout);
> +	if (ret)
> +		return ret;
> +
> +	if (test_bit(WDOG_HW_RUNNING_SUPPORTED, &wd->status)) {
> +		if (timeout)
> +			set_bit(WDOG_HW_RUNNING, &wd->status);
> +		else
> +			clear_bit(WDOG_HW_RUNNING, &wd->status);
> +	}

When we just started the watchdog we actually know that it is running,
so we could support the parameter for all watchdogs once it's started.

> +
> +	return 0;
>  }
>  EXPORT_SYMBOL(watchdog_set_timeout);
>  
> @@ -118,6 +131,15 @@ static int watchdog_register_poller(struct watchdog *wd)
>  	return PTR_ERR_OR_ZERO(p);
>  }
>  
> +static const char *watchdog_get_running(struct device_d *dev, struct param_d *p)
> +{
> +	/*
> +	 * This won't ever fail, because the parameter is only registed when
> +	 * test_bit(WDOG_HW_RUNNING_SUPPORTED, &w->status) is true
> +	 */
> +	return watchdog_hw_running((struct watchdog *)p->value) ? "1" : "0";
> +}

Casting p->value to (struct watchdog *) seems wrong. However, this
function shouldn't be needed, see below.

> +
>  static int watchdog_register_dev(struct watchdog *wd, const char *name, int id)
>  {
>  	wd->dev.parent = wd->hwdev;
> @@ -162,6 +184,15 @@ int watchdog_register(struct watchdog *wd)
>  	if (ret)
>  		return ret;
>  
> +	if (test_bit(WDOG_HW_RUNNING_SUPPORTED, &wd->status)) {
> +		p = dev_add_param(&wd->dev, "running", NULL,
> +				  watchdog_get_running, PARAM_FLAG_RO);
> +		if (IS_ERR(p))
> +			return PTR_ERR(p);
> +
> +		p->value = (char *)wd;
> +	}

How about adding this parameter unconditionally, with "unknown" as value
when WDOG_HW_RUNNING_SUPPORTED is not set. You can use
dev_add_param_enum() here.

Sascha

-- 
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