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

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Date:   Wed, 08 Nov 2017 01:23:14 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        linux-gpio@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        ckeepax@...nsource.wolfsonmicro.com, swarren@...dia.com,
        andy.shevchenko@...il.com, alcooperx@...il.com,
        bcm-kernel-feedback-list@...adcom.com, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 0/2] pinctrl: Allow indicating loss of state across suspend/resume

On Tuesday, November 7, 2017 5:00:06 PM CET Tony Lindgren wrote:
> * Florian Fainelli <f.fainelli@...il.com> [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@...il.com> [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 :)

Honestly, I'm not sure.

I'd rather have a context_lost flag to start with and see how/if
drivers will use that before adding any common infra for handling
this.

Thanks,
Rafael