linux-kernel - Re: [char-misc-next, v4, 5/7] watchdog: mei_wdt: register wd device only if required

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Date:	Sun, 17 Jan 2016 13:47:21 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	"Winkler, Tomas" <tomas.winkler@...el.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	"Usyskin, Alexander" <alexander.usyskin@...el.com>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [char-misc-next, v4, 5/7] watchdog: mei_wdt: register wd device
 only if required

On 01/17/2016 12:54 PM, Winkler, Tomas wrote:
>
>
>> -----Original Message-----
>> From: Guenter Roeck [mailto:linux@...ck-us.net]
>> Sent: Sunday, January 17, 2016 19:13
>> To: Winkler, Tomas
>> Cc: Greg Kroah-Hartman; Wim Van Sebroeck; Usyskin, Alexander; linux-
>> watchdog@...r.kernel.org; linux-kernel@...r.kernel.org
>> Subject: Re: [char-misc-next, v4, 5/7] watchdog: mei_wdt: register wd device only
>> if required
>>
>> Hi Tomas,
>>
>> On Fri, Jan 08, 2016 at 12:49:25AM +0200, Winkler, Tomas wrote:
>>> From: Alexander Usyskin <alexander.usyskin@...el.com>
>>>
>>> For Intel Broadwell and newer platforms, the ME device can inform
>>> the host whether the watchdog functionality is activated or not.
>>> If the watchdog functionality is not activated then the watchdog interface
>>> can be not registered and eliminate unnecessary pings and hence lower the
>>> power consumption by avoiding waking up the device.
>>> The feature can be deactivated also without reboot
>>> in that case the watchdog device should be unregistered at runtime.
>>>
>>> Signed-off-by: Alexander Usyskin <alexander.usyskin@...el.com>
>>> Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
>>> ---
>>> V2: rework unregistration
>>> V3: rebase; implement unregistraion also at runtime
>>> V4: Rebase the code over patchset : "watchdog: Replace driver based
>> refcounting"
>>>
>>>   drivers/watchdog/mei_wdt.c | 196
>> ++++++++++++++++++++++++++++++++++++++++++---
>>>   1 file changed, 187 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/watchdog/mei_wdt.c b/drivers/watchdog/mei_wdt.c
>>> index e7e3f144f2b0..85b27fc5d4ec 100644
>>> --- a/drivers/watchdog/mei_wdt.c
>>> +++ b/drivers/watchdog/mei_wdt.c
>>>
>> [ ... ]
>>
>>> +static void mei_wdt_unregister_work(struct work_struct *work)
>>> +{
>>> +	struct mei_wdt *wdt = container_of(work, struct mei_wdt, unregister);
>>> +
>>> +	mei_wdt_unregister(wdt);
>>> +}
>>
>> Registration is synchronous, unregistration is asynchronous.
>>
>> Assuming that is on purpose, I think it warrants an explanation.
>>
> The unregistration is detected on response from the  ping, which is run under same mutex as unregistration.
> Tomas
>
>
And that explains why registration can be synchronous and unregistration
has to be asynchronous ?

Guenter