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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>
 <0c69734d-b301-7762-7614-0644e2a719ba@roeck-us.net>
 <2a92083c-f8bd-7a42-25e2-ee6ae354a4de@ti.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <19373936-7566-3936-428a-2f2f7f3392d4@roeck-us.net>
Date:   Tue, 14 Jul 2020 00:06:17 -0700
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On 7/13/20 11:50 PM, Tero Kristo wrote:
> 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@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 ?
> 
> Re-programming of the watchdog only takes effect at the next ping, then and only then will it adjust the window size + timeout period.
> 

What a mess. I am glad this isn't hardware I have to deal with.

>>
>>
>>>       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.
> 

... and test builds on 32 bit architectures fail to compile, as reported
by 0-day. Maybe you don't care, fine, but then please remove all use of do_div
or other 64-bit divide functions from the driver and mark it as depending
on 64 bit.

>>
>>> +        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");

Maybe report what that bad window size actually is ?

>>> +            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.
> 

Seems to me that hardware team really made an effort to make the
watchdog as difficult to program as possible :-(.

> -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:
>>>
>>
> 
> -- 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki