linux-kernel - Re: [PATCH v2 10/16] gpio: add a reusable generic gpio

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Message-ID: <20200414183921.GN5412@sirena.org.uk>
Date:   Tue, 14 Apr 2020 19:39:21 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Michael Walle <michael@...le.cc>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-devicetree <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-hwmon@...r.kernel.org,
        linux-pwm@...r.kernel.org,
        LINUXWATCHDOG <linux-watchdog@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 10/16] gpio: add a reusable generic gpio_chip using
 regmap

On Tue, Apr 14, 2020 at 08:36:23PM +0200, Michael Walle wrote:
> Am 2020-04-14 19:21, schrieb Mark Brown:

> > You could define REGMAP_INVALID_ADDR to be (unsigned int)(-1) or some
> > other suitably implausible address and use that as a value.  It's
> > possible that there might be a collision with a real address on some
> > device but it should be sufficiently unlikely to be useful, especially
> > if it's not something regmap in general goes and evaluates.  For extra
> > safety we could have an API for allowing users to query the register
> > validity information regmap has (or can be given) and gpiolib could then
> > use that to figure out if the value was actually a dummy value but
> > that's probably overdoing it.

> If possible, I'd like to have the opposite logic. That is, if it is not
> set it should be invalid. If we have a magic macro like
> REGMAP_INVALID_ADDR, we must assign it to all the unused addresses. Thus
> every driver would have to assign all addresses and if in the future
> there will be some added, we'd have to touch all the drivers which use
> gpio_regmap.

Sure, for that you'd need a separate flag since zero is such a commonly
valid address.

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