Re: [PATCH 3/3] watchdog: bcm2835_wdt: set WDOG_HW_RUNNING bit when appropriate

[Guenter Roeck]

On 07/15/2016 01:15 AM, Rasmus Villemoes wrote:
> A bootloader may start the watchdog device before handing control to
> the kernel - in that case, we should tell the kernel about it so the
> watchdog framework can keep it alive until userspace opens
> /dev/watchdog0.

Separate note: The maximum timeout for this watchdog is 15 seconds.
Given that, it might be useful to set max_hw_heartbeat_ms instead of
max_timeout. Separate patch, though.

> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
> ---
>   drivers/watchdog/bcm2835_wdt.c | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
>
> diff --git a/drivers/watchdog/bcm2835_wdt.c b/drivers/watchdog/bcm2835_wdt.c
> index 4dddd82..9a08334 100644
> --- a/drivers/watchdog/bcm2835_wdt.c
> +++ b/drivers/watchdog/bcm2835_wdt.c
> @@ -55,6 +55,15 @@ struct bcm2835_wdt {
>   static unsigned int heartbeat;
>   static bool nowayout = WATCHDOG_NOWAYOUT;
>
> +static bool bcm2835_wdt_is_running(struct bcm2835_wdt *wdt)
> +{
> +	uint32_t cur;
> +
> +	cur = readl(wdt->base + PM_RSTC);
> +
> +	return !!(cur & PM_RSTC_WRCFG_FULL_RESET);
> +}
> +
>   static int bcm2835_wdt_start(struct watchdog_device *wdog)
>   {
>   	struct bcm2835_wdt *wdt = watchdog_get_drvdata(wdog);
> @@ -70,6 +79,7 @@ static int bcm2835_wdt_start(struct watchdog_device *wdog)
>   		  PM_RSTC_WRCFG_FULL_RESET, wdt->base + PM_RSTC);
>
>   	spin_unlock_irqrestore(&wdt->lock, flags);
> +	set_bit(WDOG_HW_RUNNING, &wdog->status);
You don't need to set this bit here unless the watchdog can not be stopped.

>   	return 0;
>   }
> @@ -79,6 +89,7 @@ static int bcm2835_wdt_stop(struct watchdog_device *wdog)
>   	struct bcm2835_wdt *wdt = watchdog_get_drvdata(wdog);
>
>   	writel_relaxed(PM_PASSWORD | PM_RSTC_RESET, wdt->base + PM_RSTC);
> +	clear_bit(WDOG_HW_RUNNING, &wdog->status);

... and since you clear the bit, it can be stopped. Both setting and resetting the bit
is therefore not necessary.

>   	return 0;
>   }
>
> @@ -181,6 +192,17 @@ static int bcm2835_wdt_probe(struct platform_device *pdev)
>   	watchdog_init_timeout(&bcm2835_wdt_wdd, heartbeat, dev);
>   	watchdog_set_nowayout(&bcm2835_wdt_wdd, nowayout);
>   	bcm2835_wdt_wdd.parent = &pdev->dev;
> +	if (bcm2835_wdt_is_running(wdt)) {
> +		/*
> +		 * The currently active timeout value (set by the
> +		 * bootloader) may be different from the module
> +		 * heartbeat parameter or the value in device
> +		 * tree. But we just need to set WDOG_HW_RUNNING,
> +		 * because then the framework will "immediately" ping
> +		 * the device, updating the timeout.
> +		 */
> +		set_bit(WDOG_HW_RUNNING, &bcm2835_wdt_wdd.status);
> +	}
>   	err = watchdog_register_device(&bcm2835_wdt_wdd);
>   	if (err) {
>   		dev_err(dev, "Failed to register watchdog device");