linux-kernel - Re: [PATCH v3 10/16] gpio: add a reusable generic gpio

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Message-ID: <CAMpxmJXctc5cbrjSeJxa7DfmjiVsbyhqAbEKt-gtayKhQj0Cnw@mail.gmail.com>
Date:   Mon, 25 May 2020 11:05:51 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 10/16] gpio: add a reusable generic gpio_chip using regmap

wt., 12 maj 2020 o 16:41 Michael Walle <michael@...le.cc> napisał(a):
>
> >> +
> >> +MODULE_AUTHOR("Michael Walle <michael@...le.cc>");
> >> +MODULE_DESCRIPTION("GPIO generic regmap driver core");
> >> +MODULE_LICENSE("GPL");
> >> diff --git a/include/linux/gpio-regmap.h b/include/linux/gpio-regmap.h
> >> new file mode 100644
> >> index 000000000000..a868cbcde6e9
> >> --- /dev/null
> >> +++ b/include/linux/gpio-regmap.h
> >> @@ -0,0 +1,69 @@
> >> +/* SPDX-License-Identifier: GPL-2.0-only */
> >> +
> >> +#ifndef _LINUX_GPIO_REGMAP_H
> >> +#define _LINUX_GPIO_REGMAP_H
> >> +
> >> +struct gpio_regmap;
> >> +
> >> +#define GPIO_REGMAP_ADDR_ZERO ((unsigned long)(-1))
> >> +#define GPIO_REGMAP_ADDR(addr) ((addr) ? : GPIO_REGMAP_ADDR_ZERO)
> >> +
> >
> > What if the addr is actually 0?
>
> Then the driver has to set GPIO_REGMAP_ADDR_ZERO or use the convenience
> macro GPIO_REGMAP_ADDR.
>
> So you can have
>
>    struct gpio_regmap_config config = { 0 };
>    config.reg_dat_base = 0x10;
>    config.reg_dir_out_base = 0x20;
>
> or
>
>    config.reg_dat_base = GPIO_REGMAP_ADDR_ZERO;
>
> or if you can't be sure if the RHS value might be zero:
>
>    config.reg_dat_base = GPIO_REGMAP_ADDR(reg);
>
>
> > Maybe drop GPIO_REGMAP_ADDR and require users to set unused registers
> > to GPIO_REGMAP_ADDR_ZERO?
>
> Thats bad because:
>   * you'd have to set plenty of unused base registers for a simple driver
>   * if there will be additional properties in the future, you have to
> touch
>     all other drivers, because they are initialized as 0 (ie. valid reg
> 0).
>
> >> +/**
> >> + * struct gpio_regmap_config - Description of a generic regmap
> >> gpio_chip.
> >> + *
> >> + * @parent:            The parent device
> >> + * @regmap:            The regmap used to access the registers
> >> + *                     given, the name of the device is used
> >> + * @label:             (Optional) Descriptive name for GPIO
> >> controller.
> >> + *                     If not given, the name of the device is used.
> >> + * @ngpio:             Number of GPIOs
> >> + * @reg_dat_base:      (Optional) (in) register base address
> >> + * @reg_set_base:      (Optional) set register base address
> >> + * @reg_clr_base:      (Optional) clear register base address
> >> + * @reg_dir_in_base:   (Optional) out setting register base address
> >> + * @reg_dir_out_base:  (Optional) in setting register base address
> >
> > The two above are inverted I think?
> good catch.
>
> > Also: why the limitation of only supporting one at a time?
>
> they should be exclusive, either you have a register where you set the
> output bits to one, or the input bits. Maybe this need a bit more
> context
> above. in gpio-mmio.c you can set both and both are used in
> set_direction(), but only one is read in get_direction().
>
> That being said, I have no strong opinion wether they should be
> exclusive
> or not, besides the symmetry of set_/get_direction().
>
> -michael
>

Sorry for the late response, your comments make sense to me. Are you
going to submit a v4 before the v5.8 merge window?

Bart