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

[Guenter Roeck]

On 01/17/2016 12:54 PM, Winkler, Tomas wrote:
> > -----Original Message-----
> > From: Guenter Roeck [mailto:linux@xxxxxxxxxxxx]
> > Sent: Sunday, January 17, 2016 19:13
> > To: Winkler, Tomas
> > Cc: Greg Kroah-Hartman; Wim Van Sebroeck; Usyskin, Alexander; linux-
> > watchdog@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxx>
> > > Signed-off-by: Tomas Winkler <tomas.winkler@xxxxxxxxx>
> > > ---
> > > 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