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

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Date:   Thu, 16 Apr 2020 11:27:49 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Michael Walle <michael@...le.cc>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-hwmon@...r.kernel.org, linux-pwm@...r.kernel.org,
        LINUXWATCHDOG <linux-watchdog@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        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

On Thu, Apr 2, 2020 at 10:37 PM Michael Walle <michael@...le.cc> wrote:

> There are quite a lot simple GPIO controller which are using regmap to
> access the hardware. This driver tries to be a base to unify existing
> code into one place. This won't cover everything but it should be a good
> starting point.
>
> It does not implement its own irq_chip because there is already a
> generic one for regmap based devices. Instead, the irq_chip will be
> instanciated in the parent driver and its irq domain will be associate
> to this driver.
>
> For now it consists of the usual registers, like set (and an optional
> clear) data register, an input register and direction registers.
> Out-of-the-box, it supports consecutive register mappings and mappings
> where the registers have gaps between them with a linear mapping between
> GPIO offset and bit position. For weirder mappings the user can register
> its own .xlate().
>
> Signed-off-by: Michael Walle <michael@...le.cc>

Overall I really like this driver and I think we should merge is as soon
as it is in reasonable shape and then improve on top so we can start
migrating drivers to it.

> +static int gpio_regmap_to_irq(struct gpio_chip *chip, unsigned int offset)
> +{
> +       struct gpio_regmap_data *data = gpiochip_get_data(chip);
> +       struct gpio_regmap *gpio = data->gpio;
> +
> +       /* the user might have its own .to_irq callback */
> +       if (gpio->to_irq)
> +               return gpio->to_irq(gpio, offset);
> +
> +       return irq_create_mapping(gpio->irq_domain, offset);

I think that should at least be irq_find_mapping(), the mapping should
definately not be created by the .to_irq() callback since that is just
a convenience function.

> +       if (gpio->irq_domain)
> +               chip->to_irq = gpio_regmap_to_irq;

I don't know about this.
(...)
> + * @irq_domain:                (Optional) IRQ domain if the controller is
> + *                     interrupt-capable
(...)
> +       struct irq_domain *irq_domain;

I don't think this is a good storage place for the irqdomain, we already have
gpio_irq_chip inside gpio_chip and that has an irqdomain, we should
strive to reuse that infrastructure also for regmap GPIO I think, for now
I would just leave .to_irq() out of this and let the driver deal with any
irqs.

Yours,
Linus Walleij