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Date:   Mon, 21 Feb 2022 10:59:20 +0100
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Subject: Re: [PATCHv4 3/4] watchdog: rti-wdt: attach to running watchdog
 during probe
Content-Language: en-US
From:   Jan Kiszka <jan.kiszka@siemens.com>
To:     <wim@linux-watchdog.org>, <linux@roeck-us.net>,
        <linux-watchdog@vger.kernel.org>, Nishanth Menon <nm@ti.com>
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References: <20200717132958.14304-1-t-kristo@ti.com>
 <20200717132958.14304-4-t-kristo@ti.com>
 <a80b83c6-cca5-f95c-6930-a6f3e79c6f15@siemens.com>
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On 21.02.22 10:10, Jan Kiszka wrote:
> On 17.07.20 15:29, 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@ti.com>
>> ---
>>  drivers/watchdog/rti_wdt.c | 112 +++++++++++++++++++++++++++++++++----
>>  1 file changed, 102 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
>> index d456dd72d99a..7cbdc178ffe8 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;
>> +
> 
> This seems broken: You are only adjusting the frequency value used by
> the driver. What has been programmed into the hardware already is still
> based on real frequency. Moreover, this path is not only taken when the
> watchdog is already running - but the latter case is what the subject
> and commit message suggests. I've noticed this by comparing
> bootloader-programmed values with those the driver assumes to see - 10%
> off, obviously.
> 
> So, what is actually supposed to happen here?
> 
> Jan
> 
>>  	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 +257,48 @@ 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;
>> +		do_div(heartbeat_ms, wdt->freq);
>> +		if (heartbeat_ms != heartbeat * 1000)
>> +			dev_warn(dev, "watchdog already running, ignoring heartbeat config!\n");
>> +
>> +		heartbeat = heartbeat_ms;
>> +		heartbeat /= 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;
>> +		}
>> +	}
>> +
>> +	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:
> 

There is actually more "inaccurate". For now, I would try to address it 
like this:

diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
index 88815419ad1a..1b6629fa5bfc 100644
--- a/drivers/watchdog/rti_wdt.c
+++ b/drivers/watchdog/rti_wdt.c
@@ -231,14 +231,6 @@ 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;
-
 	pm_runtime_enable(dev);
 	ret = pm_runtime_get_sync(dev);
 	if (ret) {
@@ -252,8 +244,6 @@ static int rti_wdt_probe(struct platform_device *pdev)
 	wdd->info = &rti_wdt_info;
 	wdd->ops = &rti_wdt_ops;
 	wdd->min_timeout = 1;
-	wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
-		wdt->freq * 1000;
 	wdd->parent = dev;
 
 	watchdog_set_drvdata(wdd, wdt);
@@ -280,7 +270,7 @@ static int rti_wdt_probe(struct platform_device *pdev)
 		if (heartbeat_ms != heartbeat * 1000)
 			dev_warn(dev, "watchdog already running, ignoring heartbeat config!\n");
 
-		heartbeat = heartbeat_ms;
+		heartbeat = heartbeat_ms + 500;
 		heartbeat /= 1000;
 
 		wsize = readl(wdt->base + RTIWWDSIZECTRL);
@@ -297,6 +287,17 @@ static int rti_wdt_probe(struct platform_device *pdev)
 		}
 	}
 
+	/*
+	 * 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;
+
+	wdd->max_hw_heartbeat_ms = (WDT_PRELOAD_MAX << WDT_PRELOAD_SHIFT) /
+		wdt->freq * 1000;
+
 	watchdog_init_timeout(wdd, heartbeat, dev);
 
 	ret = watchdog_register_device(wdd);


This moves the virtual frequency tweaking after reading back the 
programmed timeout. It also properly rounds that up to full seconds so 
that, e.g., bootloader-programmed programmed 60s will become 59s in the 
driver. That could have led to too short min_hw_heartbeat_ms.

I can send this out as real patch, but I'd still like to understand the 
freq fiddling first. Is that addressing a real hardware issue? Or was it 
actually papering over that round-up problem?

Jan

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