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Subject: Re: [PATCHv3 3/4] watchdog: rti-wdt: attach to running watchdog
 during probe
To:     Tero Kristo <t-kristo@ti.com>, wim@linux-watchdog.org,
        linux-watchdog@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, jan.kiszka@siemens.com
References: <20200713131818.825-1-t-kristo@ti.com>
 <20200713131818.825-4-t-kristo@ti.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <0c69734d-b301-7762-7614-0644e2a719ba@roeck-us.net>
Date:   Mon, 13 Jul 2020 22:15:41 -0700
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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@ti.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 ?


>  	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.

> +		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 ?

> +	}
> +
> +	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:
>