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

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Date:   Tue, 14 Apr 2020 19:00:30 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Michael Walle <michael@...le.cc>
Cc:     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>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 10/16] gpio: add a reusable generic gpio_chip using regmap

wt., 14 kwi 2020 o 12:07 Michael Walle <michael@...le.cc> napisał(a):
> >>
> >> So the best from a user perspective I've could come up with was:
> >>
> >>    ->base_reg = GPIO_REGMAP_ADDR(addr);
> >>
> >> I'm open for suggestions.
> >>
> >
> > Maybe setting the pointer to ERR_PTR(-ENOENT) which will result in
> > IS_ERR() returning true?
>
> Unfortunatly, its not a pointer, but only a regular unsigned int (ie
> the type the regmap API has for its "reg" property). It could be a
> pointer of course but then the user would have to allocate additional
> memory.
>
> -michael
>

Eek, of course it's not a pointer. If possible I'd like to avoid this
GPIO_REGMAP_ADDR() macro, so how about having some separate field for
invalid offsets making every offset 'valid' by default?

Linus: do you have a better idea?

Bart