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

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Date:   Tue, 7 Nov 2017 17:02:22 -0800
From:   Tony Lindgren <tony@...mide.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
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

* Rafael J. Wysocki <rjw@...ysocki.net> [171108 00:25]:
> On Tuesday, November 7, 2017 5:00:06 PM CET Tony Lindgren wrote:
> > 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.

Right, I'll provide some use cases but it will be a little while.

Currently it's done in non-generic way at the interconnect code
for my use cases:

$ git grep "\.context_offs = " arch/arm/mach-omap2/*data.c | wc -l
276

It seems that we could have genpd take care of this in a generic
way with the patch I posted.

Regards,

Tony