Date:   Tue, 14 Jul 2020 09:50:22 +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: [PATCHv3 3/4] watchdog: rti-wdt: attach to running watchdog
 during probe

On 14/07/2020 08:15, Guenter Roeck wrote:
> On 7/13/20 6:18 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 | 111 +++++++++++++++++++++++++++++++++----
>>   1 file changed, 101 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
>> index d456dd72d99a..45dfc546e371 100644
>> --- a/drivers/watchdog/rti_wdt.c
>> +++ b/drivers/watchdog/rti_wdt.c
>> @@ -35,7 +35,11 @@
>>   
>>   #define RTIWWDRX_NMI	0xa
>>   
>> -#define RTIWWDSIZE_50P	0x50
>> +#define RTIWWDSIZE_50P		0x50
>> +#define RTIWWDSIZE_25P		0x500
>> +#define RTIWWDSIZE_12P5		0x5000
>> +#define RTIWWDSIZE_6P25		0x50000
>> +#define RTIWWDSIZE_3P125	0x500000
>>   
>>   #define WDENABLE_KEY	0xa98559da
>>   
>> @@ -48,7 +52,7 @@
>>   
>>   #define DWDST			BIT(1)
>>   
>> -static int heartbeat;
>> +static int heartbeat = DEFAULT_HEARTBEAT;
>>   
>>   /*
>>    * struct to hold data for each WDT device
>> @@ -79,11 +83,9 @@ static int rti_wdt_start(struct watchdog_device *wdd)
>>   	 * be petted during the open window; not too early or not too late.
>>   	 * The HW configuration options only allow for the open window size
>>   	 * to be 50% or less than that; we obviouly want to configure the open
>> -	 * window as large as possible so we select the 50% option. To avoid
>> -	 * any glitches, we accommodate 5% safety margin also, so we setup
>> -	 * the min_hw_hearbeat at 55% of the timeout period.
>> +	 * window as large as possible so we select the 50% option.
>>   	 */
>> -	wdd->min_hw_heartbeat_ms = 11 * wdd->timeout * 1000 / 20;
>> +	wdd->min_hw_heartbeat_ms = 500 * wdd->timeout;
>>   
>>   	/* Generate NMI when wdt expires */
>>   	writel_relaxed(RTIWWDRX_NMI, wdt->base + RTIWWDRXCTRL);
>> @@ -110,7 +112,48 @@ static int rti_wdt_ping(struct watchdog_device *wdd)
>>   	return 0;
>>   }
>>   
>> -static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
>> +static int rti_wdt_setup_hw_hb(struct watchdog_device *wdd, u32 wsize)
>> +{
>> +	/*
>> +	 * RTI only supports a windowed mode, where the watchdog can only
>> +	 * be petted during the open window; not too early or not too late.
>> +	 * The HW configuration options only allow for the open window size
>> +	 * to be 50% or less than that.
>> +	 */
>> +	switch (wsize) {
>> +	case RTIWWDSIZE_50P:
>> +		/* 50% open window => 50% min heartbeat */
>> +		wdd->min_hw_heartbeat_ms = 500 * heartbeat;
>> +		break;
>> +
>> +	case RTIWWDSIZE_25P:
>> +		/* 25% open window => 75% min heartbeat */
>> +		wdd->min_hw_heartbeat_ms = 750 * heartbeat;
>> +		break;
>> +
>> +	case RTIWWDSIZE_12P5:
>> +		/* 12.5% open window => 87.5% min heartbeat */
>> +		wdd->min_hw_heartbeat_ms = 875 * heartbeat;
>> +		break;
>> +
>> +	case RTIWWDSIZE_6P25:
>> +		/* 6.5% open window => 93.5% min heartbeat */
>> +		wdd->min_hw_heartbeat_ms = 935 * heartbeat;
>> +		break;
>> +
>> +	case RTIWWDSIZE_3P125:
>> +		/* 3.125% open window => 96.9% min heartbeat */
>> +		wdd->min_hw_heartbeat_ms = 969 * heartbeat;
>> +		break;
>> +
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static unsigned int rti_wdt_get_timeleft_ms(struct watchdog_device *wdd)
>>   {
>>   	u64 timer_counter;
>>   	u32 val;
>> @@ -123,11 +166,18 @@ static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
>>   
>>   	timer_counter = readl_relaxed(wdt->base + RTIDWDCNTR);
>>   
>> +	timer_counter *= 1000;
>> +
>>   	do_div(timer_counter, wdt->freq);
>>   
>>   	return timer_counter;
>>   }
>>   
>> +static unsigned int rti_wdt_get_timeleft(struct watchdog_device *wdd)
>> +{
>> +	return rti_wdt_get_timeleft_ms(wdd) / 1000;
>> +}
>> +
>>   static const struct watchdog_info rti_wdt_info = {
>>   	.options = WDIOF_KEEPALIVEPING,
>>   	.identity = "K3 RTI Watchdog",
>> @@ -148,6 +198,7 @@ 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)
>> @@ -169,6 +220,14 @@ static int rti_wdt_probe(struct platform_device *pdev)
>>   		return -EINVAL;
>>   	}
>>   
>> +	/*
>> +	 * If watchdog is running at 32k clock, it is not accurate.
>> +	 * Adjust frequency down in this case so that we don't pet
>> +	 * the watchdog too often.
>> +	 */
>> +	if (wdt->freq < 32768)
>> +		wdt->freq = wdt->freq * 9 / 10;
>> +
> 
> So this is now only a problem is the window size was set restrictively
> in the BOS/ROMMON. Meaning it is still a problem. How is this better than
> before ? Why not just always set the window size to something reasonable ?

Re-programming of the watchdog only takes effect at the next ping, then 
and only then will it adjust the window size + timeout period.

> 
> 
>>   	pm_runtime_enable(dev);
>>   	ret = pm_runtime_get_sync(dev);
>>   	if (ret) {
>> @@ -185,11 +244,8 @@ 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;
>>   	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);
>> @@ -201,12 +257,47 @@ static int rti_wdt_probe(struct platform_device *pdev)
>>   		goto err_iomap;
>>   	}
>>   
>> +	if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
>> +		u32 time_left_ms;
>> +		u64 heartbeat_ms;
>> +		u32 wsize;
>> +
>> +		set_bit(WDOG_HW_RUNNING, &wdd->status);
>> +		time_left_ms = rti_wdt_get_timeleft_ms(wdd);
>> +		heartbeat_ms = readl(wdt->base + RTIDWDPRLD);
>> +		heartbeat_ms <<= WDT_PRELOAD_SHIFT;
>> +		heartbeat_ms *= 1000;
>> +		heartbeat_ms /= wdt->freq;
> 
> Ah yes, the pitfalls of 64-bit divide operations.

Should I convert this to use do_div? With 64bit archs this code is 
targeted at it runs just fine.

> 
>> +		if (heartbeat_ms / 1000 != heartbeat)
>> +			dev_warn(dev, "watchdog already running, ignoring heartbeat config!\n");
>> +
>> +		heartbeat = heartbeat_ms / 1000;
>> +
>> +		wsize = readl(wdt->base + RTIWWDSIZECTRL);
>> +		ret = rti_wdt_setup_hw_hb(wdd, wsize);
>> +		if (ret) {
>> +			dev_err(dev, "bad window size.\n");
>> +			goto err_iomap;
>> +		}
>> +
>> +		last_ping = heartbeat_ms - time_left_ms;
>> +		if (time_left_ms > heartbeat_ms) {
>> +			dev_warn(dev, "time_left > heartbeat? Assuming last ping just before now.\n");
>> +			last_ping = 0;
>> +		}
> 
> All that complexity makes me wonder if it wouldn't be better to just reprogram
> the watchdog if it is already running. Any reason for not doing that ?

Well, you can re-program it but... It does not take effect until next 
window starts, so basically we need to take care of the currently 
running window anyways after which re-programming it doesn't make much 
sense anymore. And handling the switch from one setup to next would add 
extra complexity.

-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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