linux-kernel - Re: [PATCH V2 1/3] watchdog: imgpdc: Allow timeout to be set in device-tree

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Message-ID: <CAL1qeaF7v2EPB0BYdS_d+UAcFEJiB2KRes23PymtUsKu1y=moQ@mail.gmail.com>
Date:	Thu, 2 Apr 2015 09:46:04 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	James Hogan <james.hogan@...tec.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ezequiel Garcia <ezequiel.garcia@...tec.com>
Subject: Re: [PATCH V2 1/3] watchdog: imgpdc: Allow timeout to be set in device-tree

On Wed, Apr 1, 2015 at 6:08 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 04/01/2015 03:22 PM, James Hogan wrote:
>>
>> Hi Andrew,
>>
>> On Wed, Apr 01, 2015 at 10:43:14AM -0700, Andrew Bresticker wrote:
>>>
>>> Since the heartbeat is statically initialized to its default value,
>>> watchdog_init_timeout() will never look in the device-tree for a
>>> timeout-sec value.  Instead of statically initializing heartbeat,
>>> fall back to the default timeout value if watchdog_init_timeout()
>>> fails.
>>
>>
>> Whoops. Sorry about that. I wasn't aware that a timeout-sec value was
>> expected. It isn't mentioned in the DT binding documentation for this
>> device :-(.
>>
>>>
>>> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
>>> Cc: Ezequiel Garcia <ezequiel.garcia@...tec.com>
>>> Cc: James Hogan <james.hogan@...tec.com>
>>> ---
>>> New for v2.
>>> ---
>>>   drivers/watchdog/imgpdc_wdt.c | 6 +++---
>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/watchdog/imgpdc_wdt.c
>>> b/drivers/watchdog/imgpdc_wdt.c
>>> index 0deaa4f..89b2abc 100644
>>> --- a/drivers/watchdog/imgpdc_wdt.c
>>> +++ b/drivers/watchdog/imgpdc_wdt.c
>>> @@ -42,7 +42,7 @@
>>>   #define PDC_WDT_MIN_TIMEOUT           1
>>>   #define PDC_WDT_DEF_TIMEOUT           64
>>>
>>> -static int heartbeat = PDC_WDT_DEF_TIMEOUT;
>>> +static int heartbeat;
>>>   module_param(heartbeat, int, 0);
>>>   MODULE_PARM_DESC(heartbeat, "Watchdog heartbeats in seconds "
>>>         "(default=" __MODULE_STRING(PDC_WDT_DEF_TIMEOUT) ")");
>>> @@ -195,9 +195,9 @@ static int pdc_wdt_probe(struct platform_device
>>> *pdev)
>>>
>>>         ret = watchdog_init_timeout(&pdc_wdt->wdt_dev, heartbeat,
>>> &pdev->dev);
>>>         if (ret < 0) {
>>> -               pdc_wdt->wdt_dev.timeout = pdc_wdt->wdt_dev.max_timeout;
>>> +               pdc_wdt->wdt_dev.timeout = PDC_WDT_DEF_TIMEOUT;
>>
>>
>> The watchdog_init_timeout kerneldoc comment suggests that the old value
>> should be the default timeout, i.e. that timeout should be set to
>> PDC_WDT_DEF_TIMEOUT before calling watchdog_init_timeout, rather than
>> whenever ret < 0.
>>
>> Indeed, if heartbeat is set to an invalid non-zero value,
>> watchdog_init_timeout will still try and set timeout from DT, but also
>> still returns -EINVAL regardless of whether that succeeds, and this
>> would incorrectly override the timeout from DT with the hardcoded
>> default.
>>
>>>                 dev_warn(&pdev->dev,
>>> -                        "Initial timeout out of range! setting max
>>> timeout\n");
>>> +                        "Initial timeout out of range! setting default
>>> timeout\n");
>>
>>
>> It feels wrong for a presumably safe & normal situation (i.e. no default
>> in DT, which arguably shouldn't contain policy anyway) to show a
>> warning, but it can also show due to an invalid module parameter (or
>> invalid DT property) which is most definitely justified.
>>
>
> Agreed. I would suggest to leave that part alone and set the default prior
> to calling watchdog_init_timeout().

Yes, but I think James' concern here was that we'd now get a
dev_warn() in the normal case where no timeout is specified via module
parameter or DT.
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