linux-kernel - Re: [PATCH 2/2] watchdog: rti: tweak min_hw_heartbeat

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Date:   Thu, 25 Jun 2020 20:04:50 +0300
From:   Tero Kristo <t-kristo@...com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Jan Kiszka <jan.kiszka@...mens.com>, <wim@...ux-watchdog.org>,
        <linux-watchdog@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] watchdog: rti: tweak min_hw_heartbeat_ms to match
 initial allowed window

On 25/06/2020 16:35, Guenter Roeck wrote:
> On 6/25/20 1:32 AM, Tero Kristo wrote:
>> On 24/06/2020 18:24, Jan Kiszka wrote:
>>> On 24.06.20 13:45, Tero Kristo wrote:
>>>> If the RTI watchdog has been started by someone (like bootloader) when
>>>> the driver probes, we must adjust the initial ping timeout to match the
>>>> currently running watchdog window to avoid generating watchdog reset.
>>>>
>>>> Signed-off-by: Tero Kristo <t-kristo@...com>
>>>> ---
>>>>    drivers/watchdog/rti_wdt.c | 25 +++++++++++++++++++++++++
>>>>    1 file changed, 25 insertions(+)
>>>>
>>>> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
>>>> index d456dd72d99a..02ea2b2435f5 100644
>>>> --- a/drivers/watchdog/rti_wdt.c
>>>> +++ b/drivers/watchdog/rti_wdt.c
>>>> @@ -55,11 +55,13 @@ static int heartbeat;
>>>>     * @base - base io address of WD device
>>>>     * @freq - source clock frequency of WDT
>>>>     * @wdd  - hold watchdog device as is in WDT core
>>>> + * @min_hw_heartbeat_save - save of the min hw heartbeat value
>>>>     */
>>>>    struct rti_wdt_device {
>>>>        void __iomem        *base;
>>>>        unsigned long        freq;
>>>>        struct watchdog_device    wdd;
>>>> +    unsigned int        min_hw_heartbeat_save;
>>>>    };
>>>>    static int rti_wdt_start(struct watchdog_device *wdd)
>>>> @@ -107,6 +109,11 @@ static int rti_wdt_ping(struct watchdog_device *wdd)
>>>>        /* put watchdog in active state */
>>>>        writel_relaxed(WDKEY_SEQ1, wdt->base + RTIWDKEY);
>>>> +    if (wdt->min_hw_heartbeat_save) {
>>>> +        wdd->min_hw_heartbeat_ms = wdt->min_hw_heartbeat_save;
>>>> +        wdt->min_hw_heartbeat_save = 0;
>>>> +    }
>>>> +
>>>>        return 0;
>>>>    }
>>>> @@ -201,6 +208,24 @@ static int rti_wdt_probe(struct platform_device *pdev)
>>>>            goto err_iomap;
>>>>        }
>>>> +    if (readl(wdt->base + RTIDWDCTRL) == WDENABLE_KEY) {
>>>> +        u32 time_left;
>>>> +        u32 heartbeat;
>>>> +
>>>> +        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;
>>>> +        if (time_left < heartbeat / 2)
>>>> +            wdd->min_hw_heartbeat_ms = 0;
>>>> +        else
>>>> +            wdd->min_hw_heartbeat_ms =
>>>> +                (time_left - heartbeat / 2 + 1) * 1000;
>>>> +
>>>> +        wdt->min_hw_heartbeat_save = 11 * heartbeat * 1000 / 20;
>>>> +    }
>>>> +
>>>>        ret = watchdog_register_device(wdd);
>>>>        if (ret) {
>>>>            dev_err(dev, "cannot register watchdog device\n");
>>>>
>>>
>>> This assumes that the bootloader also programmed a 50% window, right? The pending U-Boot patch will do that, but what if that may chance or someone uses a different setup?
>>
>> Yes, we assume 50%. I think based on the hw design, 50% is the only sane value to be used, otherwise you just shrink the open window too much and for no apparent reason.
>>
> 
> Not sure if that is a valid assumption. Someone who designs a watchdog
> with such a narrow ping window might as well also use it. The question
> is if you want to rely on that assumption, or check and change it if needed.

Right, if that is a blocker, I can modify the code. Should be maybe 
couple of lines addition.

> Also, I wonder if we should add an API function such as
> "set_last_hw_keepalive()" to avoid all that complexity.

I can try adding that also if it is desirable.

-Tero
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