linux-kernel - Re: [PATCHv2 4/5] watchdog: rti-wdt: attach to running watchdog during probe

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Date:   Sun, 5 Jul 2020 08:07:33 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Tero Kristo <t-kristo@...com>, wim@...ux-watchdog.org,
        linux-watchdog@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, jan.kiszka@...mens.com
Subject: Re: [PATCHv2 4/5] watchdog: rti-wdt: attach to running watchdog
 during probe

On 7/3/20 5:04 AM, Tero Kristo wrote:
> If the RTI watchdog is running already during probe, the driver must
> configure itself to match the HW. Window size and timeout is probed from
> hardware, and the last keepalive ping is adjusted to match it also.
> 
> Signed-off-by: Tero Kristo <t-kristo@...com>
> ---
>  drivers/watchdog/rti_wdt.c | 26 +++++++++++++++++++++++---
>  1 file changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 110bfc8d0bb3..987e5a798cb4 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -213,6 +213,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
>  	struct watchdog_device *wdd;
>  	struct rti_wdt_device *wdt;
>  	struct clk *clk;
> +	u32 last_ping = 0;
>  
>  	wdt = devm_kzalloc(dev, sizeof(*wdt), GFP_KERNEL);
>  	if (!wdt)
> @@ -258,11 +259,8 @@ static int rti_wdt_probe(struct platform_device *pdev)
>  	wdd->min_timeout = 1;
>  	wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
>  		wdt->freq * 1000;
> -	wdd->timeout = DEFAULT_HEARTBEAT;

What if the watchdog is not running ?

>  	wdd->parent = dev;
>  
> -	watchdog_init_timeout(wdd, heartbeat, dev);
> -
>  	watchdog_set_drvdata(wdd, wdt);
>  	watchdog_set_nowayout(wdd, 1);
>  	watchdog_set_restart_priority(wdd, 128);
> @@ -274,12 +272,34 @@ static int rti_wdt_probe(struct platform_device *pdev)
>  		goto err_iomap;
>  	}
>  
> +	if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
> +		u32 time_left;
> +
> +		set_bit(WDOG_HW_RUNNING, &wdd->status);
> +		time_left = rti_wdt_get_timeleft(wdd);
> +		heartbeat = readl(wdt->base + RTIDWDPRLD);
> +		heartbeat <<= WDT_PRELOAD_SHIFT;
> +		heartbeat /= wdt->freq;
> +

This ignores any heartbeat configured as module parameter, which most
people will consider unexpected. It might be worthwhile documenting that.

> +		wsize = readl(wdt->base + RTIWWDSIZECTRL);
> +		ret = rti_wdt_setup_hw_hb(wdd);
> +		if (ret)
> +			goto err_iomap;
> +
> +		last_ping = -(time_left - heartbeat) * 1000;

Why the double negation ?

		last_ping = (heartbeat - time_left) * 1000;

seems simpler. Also, what if heartbeat - time_left is negative for whatever
reason ?

I am not sure if it is a good idea to call rti_wdt_get_timeleft()
here. It might be better to add a helper function such as
rti_wdt_get_timeleft_ms() to return the time left in milli-seconds
for improved accuracy.

> +	}
> +
> +	watchdog_init_timeout(wdd, heartbeat, dev);
> +
>  	ret = watchdog_register_device(wdd);
>  	if (ret) {
>  		dev_err(dev, "cannot register watchdog device\n");
>  		goto err_iomap;
>  	}
>  
> +	if (last_ping)
> +		watchdog_set_last_hw_keepalive(wdd, last_ping);
> +
>  	return 0;
>  
>  err_iomap:
>