Re: [PATCH v4] PM / devfreq: Restart previous governor if new governor fails to start

[Sibi Sankar]

Hey MyungJoo, Kyungmin
Did you get a chance to think about how you
want this fix implemented?

On 2019-02-19 10:42, Sibi Sankar wrote:
> Hey MyungJoo,
>
> On 12/14/18 7:15 AM, MyungJoo Ham wrote:
> > > From: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
> > >
> > > If the new governor fails to start, switch back to old governor so 
> > > that the
> > > devfreq state is not left in some weird limbo.
> > >
> > > Signed-off-by: Sibi Sankar <sibis@xxxxxxxxxxxxxx>
> > > Signed-off-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
> > > Reviewed-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
> >
> > Hello,
> >
> > In overall, the idea and the implementation looks good.
> >
> > However, I have a question:
> >
> > What if the following line fails?
> >
> > +		df->governor->event_handler(df, DEVFREQ_GOV_START,
> > +					    NULL);
> >
> > Don't we still need something to handle for such events?
>
> The original discussion went as follows:
> governor_store is expected to be used only on cases
> where devfreq_add_device() succeeded i.e prev->governor
> is expected to be present and DEVFREQ_GOV_START is
> expected to succeed. Hence falling back to the previous
> governor seems like a sensible idea.
>
> This would also prevent DEVFREQ_GOV_STOP from being called
> on a governor were DEVFREQ_GOV_START had failed which is
> ideal.
>
> That being said DEVFREQ_GOV_START can still fail for the
> prev-governor due to some change in state of the system.
> Do you want to handle this case by clearing the state of
> governor rather than switching to previous governor?
>
> > Cheers,
> > MyungJoo

--
-- Sibi Sankar --
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