linux-kernel - Re: [PATCH 1/2] pinctrl: Allow a device to indicate when to force a state

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Date:   Tue, 26 Sep 2017 15:16:28 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Florian Fainelli <f.fainelli@...il.com>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        ext Tony Lindgren <tony@...mide.com>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Warren <swarren@...dia.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Al Cooper <alcooperx@...il.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH 1/2] pinctrl: Allow a device to indicate when to force a
 state

On Fri, Sep 22, 2017 at 09:57:22AM -0700, Florian Fainelli wrote:
> On 09/22/2017 06:20 AM, Charles Keepax wrote:
> > On Fri, Sep 22, 2017 at 01:55:22PM +0200, Linus Walleij wrote:
> >> On Thu, Sep 21, 2017 at 3:04 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
> > I guess in our case we didn't really consider the restore aspect
> > because we essentially get that for free from regmap. Regmap
> > cache's all our register state and provides a mechanism to sync
> > that back to the hardware, so we simply invoke that on resume and
> > all our GPIO/pinctrl state is restored.
> 
> As you may see, the problem in my case is that the hardware has only onw
> pinctrl state: "default", and it loses its hardware register contents,
> and because of early check in pinctrl_select_state(), we do nothing (the
> state has not changed per-se), so we are left with SW thinking we
> applied the "default" state again, while in fact we did not.
> 

That is exactly the situation we have on the CODECs when they go
into runtime suspend, power is removed, and everything is back at
defaults when we resume. Just in our case we re-apply the state
as part of the CODEC resume using a regmap sync.

> The approach taken here was to move this to the core pinctrl code
> because this is not something a pinctrl consumer should be aware of,
> when it calls pinctrl_select_state(), it should do what it asked for.
> 

Apologies if I have missed something here, but does the consumer
not still to some extent need to be aware with this solution
since it needs to re-request the pin state in resume?

I think that is really my only reservation here, is it feels
like this should be something that is purely implemented on the
provider, and be invisible to the consumer, and I am not clear
this is.

> I also decided to make this a per-provider property as opposed to a
> per-group property because chances are that the state retention is on a
> per-controller basis, and not per-bank/group, although I may be wrong.
> 

It seems quite likely that this property would mostly be
per-provider to me as well.

Thanks,
Charles