Message-ID: <2b79e1ac-3399-075d-1d1d-e6d7f88351fc@starfivetech.com>
Date:   Mon, 27 Feb 2023 14:45:52 +0800
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Subject: Re: [PATCH v3 2/2] drivers: watchdog: Add StarFive Watchdog driver
Content-Language: en-US
To:     Guenter Roeck <linux@roeck-us.net>
CC:     <linux-riscv@lists.infradead.org>, <devicetree@vger.kernel.org>,
        <linux-watchdog@vger.kernel.org>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        "Palmer Dabbelt" <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "Philipp Zabel" <p.zabel@pengutronix.de>,
        Samin Guo <samin.guo@starfivetech.com>,
        <linux-kernel@vger.kernel.org>, Conor Dooley <conor@kernel.org>
References: <20230220081926.267695-1-xingyu.wu@starfivetech.com>
 <20230220081926.267695-3-xingyu.wu@starfivetech.com>
 <20230223182341.GA200380@roeck-us.net>
 <8ba002ea-299c-2eaf-b1a7-d7d38a540152@starfivetech.com>
 <ae998eb6-54ce-05c4-2961-bdb2393eac64@roeck-us.net>
 <58cab864-2a59-b82c-bdfe-2e805a04fd7a@starfivetech.com>
 <547a469d-eeaa-750c-4fe5-cc82d92493a6@roeck-us.net>
From:   Xingyu Wu <xingyu.wu@starfivetech.com>
In-Reply-To: <547a469d-eeaa-750c-4fe5-cc82d92493a6@roeck-us.net>
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Precedence: bulk

On 2023/2/27 14:36, Guenter Roeck wrote:
> On 2/26/23 22:26, Xingyu Wu wrote:
>> On 2023/2/24 23:18, Guenter Roeck wrote:
>>> On 2/23/23 23:42, Xingyu Wu wrote:
>>>> On 2023/2/24 2:23, Guenter Roeck wrote:
>>>>> On Mon, Feb 20, 2023 at 04:19:26PM +0800, Xingyu Wu wrote:
>>>>>> [...]
>>>>>> +
>>>>>> +    wdt->wdt_device.min_timeout = 1;
>>>>>> +    wdt->wdt_device.max_timeout = starfive_wdt_max_timeout(wdt);
>>>>>
>>>>>      wdt->wdt_device.timeout = STARFIVE_WDT_DEFAULT_TIME;
>>>>>
>>>>> should be set here. Otherwise the warning below would always be seen
>>>>> if the module parameter is not set.
>>>>>
>>>>>> +
>>>>>> +    watchdog_set_drvdata(&wdt->wdt_device, wdt);
>>>>>> +
>>>>>> +    /*
>>>>>> +     * see if we can actually set the requested heartbeat,
>>>>>> +     * and if not, try the default value.
>>>>>> +     */
>>>>>> +    watchdog_init_timeout(&wdt->wdt_device, heartbeat, dev);
>>>>>> +    if (wdt->wdt_device.timeout == 0 ||
>>>>>
>>>>> If wdt->wdt_device.timeout is pre-initialized, it will never be 0 here.
>>>>>
>>>>>> +        wdt->wdt_device.timeout > wdt->wdt_device.max_timeout) {
>>>>>
>>>>> That won't happen because watchdog_init_timeout() validates it and does
>>>>> not update the value if it is out of range.
>>>>>
>>>>>> +        dev_warn(dev, "heartbeat value out of range, default %d used\n",
>>>>>> +             STARFIVE_WDT_DEFAULT_TIME);
>>>>>> +        wdt->wdt_device.timeout = STARFIVE_WDT_DEFAULT_TIME;
>>>>>
>>>>> And this is then unnecessary. wdt->wdt_device.timeout will always be
>>>>> valid if it was pre-initialized.
>>>>
>>>> It is changed to be this at beginning of the driver:
>>>>
>>>> static int heartbeat = STARFIVE_WDT_DEFAULT_TIME;
>>>>
>>>
>>> No, this is wrong. The static variable should be set to 0 to indicate
>>> "use default".
>>>
>>>> and it is changed to be this here:
>>>>
>>>> ret = watchdog_init_timeout(&wdt->wdt_device, heartbeat, dev);
>>>> if (ret)
>>>>      return ret;
>>>>
>>>> Would that be better?
>>>>
>>>
>>> No, it is worse, because it would not instantiate the watchdog at all
>>> if a bad heartbeat is provided.
>>>
>>
>> So instantiate the watchdog with hearbeat first. And if this wrong, use default timeout.
>> :
>> if (watchdog_init_timeout(&wdt->wdt_device, heartbeat, dev))
>>     wdt->wdt_device.timeout = STARFIVE_WDT_DEFAULT_TIME;
>>
> 
> I am kind of lost why you have to make it that complicated.
> Just pre-initialize wdt->wdt_device.timeout like all the other drivers do,
> and as I had suggested earlier.
> 

So you mean just use :
wdt->wdt_device.timeout = STARFIVE_WDT_DEFAULT_TIME;
to initialize watchdog directly?

Best regards,
Xingyu Wu