linux-kernel - Re: [PATCH v2 3/8] watchdog: JZ4740: Register a restart handler

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Date:   Sat, 20 Jan 2018 21:34:35 +0530
From:   PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Wim Van Sebroeck <wim@...ana.be>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-MIPS <linux-mips@...ux-mips.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v2 3/8] watchdog: JZ4740: Register a restart handler

Hi Guenter,

On 20 January 2018 at 21:15, Guenter Roeck <linux@...ck-us.net> wrote:
> On 01/19/2018 11:31 PM, PrasannaKumar Muralidharan wrote:
>>
>> Hi Paul,
>>
>> On 30 December 2017 at 19:21, Paul Cercueil <paul@...pouillou.net> wrote:
>>>
>>> The watchdog driver can restart the system by simply configuring the
>>> hardware for a timeout of 0 seconds.
>>>
>>> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
>>> ---
>>>   drivers/watchdog/jz4740_wdt.c | 9 +++++++++
>>>   1 file changed, 9 insertions(+)
>>>
>>>   v2: No change
>>>
>>> diff --git a/drivers/watchdog/jz4740_wdt.c
>>> b/drivers/watchdog/jz4740_wdt.c
>>> index 92d6ca8ceb49..fa7f49a3212c 100644
>>> --- a/drivers/watchdog/jz4740_wdt.c
>>> +++ b/drivers/watchdog/jz4740_wdt.c
>>> @@ -130,6 +130,14 @@ static int jz4740_wdt_stop(struct watchdog_device
>>> *wdt_dev)
>>>          return 0;
>>>   }
>>>
>>> +static int jz4740_wdt_restart(struct watchdog_device *wdt_dev,
>>> +                             unsigned long action, void *data)
>>> +{
>>> +       wdt_dev->timeout = 0;
>>> +       jz4740_wdt_start(wdt_dev);
>>> +       return 0;
>>> +}
>>> +
>>>   static const struct watchdog_info jz4740_wdt_info = {
>>>          .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
>>> WDIOF_MAGICCLOSE,
>>>          .identity = "jz4740 Watchdog",
>>> @@ -141,6 +149,7 @@ static const struct watchdog_ops jz4740_wdt_ops = {
>>>          .stop = jz4740_wdt_stop,
>>>          .ping = jz4740_wdt_ping,
>>>          .set_timeout = jz4740_wdt_set_timeout,
>>> +       .restart = jz4740_wdt_restart,
>>>   };
>>>
>>>   #ifdef CONFIG_OF
>>> --
>>> 2.11.0
>>>
>>>
>>
>> Noticed that min_timeout of the watchdog device is set to 1 but this
>> function calls start with timeout set to 0. Even though this works I
>> feel it is better to set min_timeout to 0.
>>
>
> No. That would be wrong. If you want to be pedantic, write a new function
> __jz4740_wdt_set_timeout(u16 clock_div, u16 timeout_value) and call it
> instead, but don't mess with min_timeout.
>
> Guenter

What is the effect of changing min_timeout? I could see only
validation checks with it.

Thanks,
PrasannaKumar