linux-kernel - Re: [RFC PATCH 1/5] gpio: gpiolib: Add core support for maintaining GPIO values on reset

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Message-ID: <1508487855.24322.49.camel@aj.id.au>
Date:   Fri, 20 Oct 2017 18:54:15 +1030
From:   Andrew Jeffery <andrew@...id.au>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Joel Stanley <joel@....id.au>,
        Ryan Chen <ryan_chen@...eedtech.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        patches@...nsource.cirrus.com,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        linux-aspeed@...ts.ozlabs.org
Subject: Re: [RFC PATCH 1/5] gpio: gpiolib: Add core support for maintaining
 GPIO values on reset

On Fri, 2017-10-20 at 09:17 +0200, Linus Walleij wrote:
> > On Fri, Oct 20, 2017 at 5:37 AM, Andrew Jeffery <andrew@...id.au> wrote:
> 
> > GPIO state reset tolerance is implemented in gpiolib through the
> > addition of a new pinconf parameter. With that, some renaming of helpers
> > is done to clarify the scope of the already existing
> > gpiochip_line_is_persistent(), as it's now ambiguous as to whether that
> > means on suspend, reset or both.
> 
> Isn't it most reasonable to say persistance covers both cases, reset
> and/or sleep? This seems a bit like overdefined.

I definitely had some internal debate about that. I erred on the side of
avoiding potential change in expectations for the arizona. If you consider that
overdefined then I'm happy to go the other way.

> 
> So can we say that is this flag is set, the hardware and driver should
> do its best to preserve the value across any system disruptions.
> 
> We can change the wording of course, patches welcome for that.

Yep.

> 
> But do we really need to distinguish the cases of disruption and
> whether we cover up for them or not?
> 
> I would say we can deal with that the day we have a system with
> two register bits (or similar) where you can select to preserve across
> sleep, reset, one or the other, AND there is also a usecase such that
> a user wants to preserve the value across reset but not suspend or
> vice versa.
> 
> I suspect that will not happen.

A very reasonable approach.

Cheers for the feedback.

Andrew
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