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

[Sibi Sankar]

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

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