Re: [PATCH v2 0/2] pinctrl: Allow indicating loss of state across suspend/resume

[Tony Lindgren]

* Florian Fainelli <f.fainelli@xxxxxxxxx> [171104 17:21]:
> 
> 
> On 11/04/2017 05:25 AM, Rafael J. Wysocki wrote:
> > On Friday, November 3, 2017 6:33:53 PM CET Tony Lindgren wrote:
> >> * Florian Fainelli <f.fainelli@xxxxxxxxx> [171103 17:04]:
> >>> On 11/03/2017 09:11 AM, Tony Lindgren wrote:
> >>> The pinctrl provider is losing its state, hence these two patches.
> >>
> >> OK
> >>
> >>>> Anyways, the context lost flag should be managed in the PM core for
> >>>> the device, so adding linux-pm and Rafael to Cc.
> >>>
> >>> I don't think it's that simple but sure, why not.
> >>
> >> Just having bool context_lost in struct dev_pm_info would probably
> >> be enough to allow drivers to deal with it. This flag could then
> >> be set for a device by power domain related code that knows if
> >> context got lost.
> > 
> > Something like: if the driver sees "context_lost" set, it should restore
> > the context to the device from memory?
> 
> That is what is being proposed here, except that the actual mechanism
> where this matters needs to be in the core pinctrl code, otherwise the
> state (context) is not restored due to a check that attempts not to
> (re)apply a previous state.
> 
> > 
> > But the it would also need to save the context beforehand, so why not to
> > restore it unconditionally on resume?
> 
> That's what my original attempts did here:
> 
> https://patchwork.kernel.org/patch/9598969/
> 
> but Linus rightfully requested this to be done differently, hence this
> attempt now to solve it in a slightly more flexible way based on DT
> properties.

For runtime PM, restoring the state constantly is unnecessary and not
good for battery life. The logic can be just:

1. Device driver runtime PM suspend saves the state when needed

2. Device driver runtime PM resume checks if context_lost was set by
   the bus or power domain code

3. If context was lost, device driver restores the state, or in some
   cases may need re-run the driver register init related parts
   to bring the driver back up, then clears the context_lost flag

How about something like the following patch? So far only compile
tested with CONFIG_PM enabled. If that looks like the way to go,
I'll test it properly and add some comments for the functions and
post a proper patch :)

Regards,

Tony

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