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

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Date:   Mon, 13 Jul 2020 15:55:02 +0300
From:   Tero Kristo <t-kristo@...com>
To:     Guenter Roeck <linux@...ck-us.net>, <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 05/07/2020 18:07, Guenter Roeck wrote:
> 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 ?

Configuring wdd->timeout seems redundant, it gets set by the 
watchdog_init_timeout call done later. I just moved that post the check 
for a running watchdog so that the same call is used for both cases.

> 
>>   	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.

I'll add a dev_warn for this case.

> 
>> +		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 ?

Will fix. I'll add a dev_warn for that case and assume last ping to be zero.

> 
> 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.

Will add that.

-Tero

> 
>> +	}
>> +
>> +	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:
>>
> 

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