linux-kernel - Re: [PATCH v4 2/2] i2c: mux: ltc4306: LTC4306 and LTC4305 I2C multiplexer/switch

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Date:   Mon, 10 Apr 2017 22:04:04 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Michael Hennerich <michael.hennerich@...log.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Peter Rosin <peda@...ntia.se>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] i2c: mux: ltc4306: LTC4306 and LTC4305 I2C multiplexer/switch

On Wed, Apr 5, 2017 at 3:07 PM,  <michael.hennerich@...log.com> wrote:

> From: Michael Hennerich <michael.hennerich@...log.com>
>
> This patch adds support for the Analog Devices / Linear Technology
> LTC4306 and LTC4305 4/2 Channel I2C Bus Multiplexer/Switches.
> The LTC4306 optionally provides two general purpose input/output pins
> (GPIOs) that can be configured as logic inputs, opendrain outputs or
> push-pull outputs via the generic GPIOLIB framework.
>
> Signed-off-by: Michael Hennerich <michael.hennerich@...log.com>

Okay!

> +#include <linux/device.h>
> +#include <linux/gpio.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/gpio/driver.h>

Why are you including all these?
Normally a GPIO driver should just include
<linux/gpio/driver.h>

> +#include <linux/i2c-mux.h>
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>

> +static int ltc4306_gpio_get(struct gpio_chip *chip, unsigned int offset)
> +{
> +       struct ltc4306 *data = gpiochip_get_data(chip);
> +       unsigned int val;
> +       int ret;
> +
> +       ret = regmap_read(data->regmap, LTC_REG_CONFIG, &val);
> +       if (ret < 0)
> +               return ret;
> +
> +       return (val & BIT(1 - offset));

Do this:

return !!(val & BIT(1 - offset));

So you clamp the return value to [0,1]

> +static int ltc4306_gpio_set_config(struct gpio_chip *chip,
> +                                  unsigned int offset, unsigned long config)
> +{
> +       struct ltc4306 *data = gpiochip_get_data(chip);
> +       unsigned int val;
> +
> +       switch (pinconf_to_config_param(config)) {
> +       case PIN_CONFIG_DRIVE_OPEN_DRAIN:
> +               val = 0;
> +               break;
> +       case PIN_CONFIG_DRIVE_PUSH_PULL:
> +               val = BIT(4 - offset);
> +               break;
> +       default:
> +               return -ENOTSUPP;
> +       }
> +
> +       return regmap_update_bits(data->regmap, LTC_REG_MODE,
> +                                 BIT(4 - offset), val);
> +}

Nice!

> +       data->gpiochip.label = dev_name(dev);
> +       data->gpiochip.base = -1;
> +       data->gpiochip.ngpio = data->chip->num_gpios;
> +       data->gpiochip.parent = dev;
> +       data->gpiochip.can_sleep = true;
> +       data->gpiochip.direction_input = ltc4306_gpio_direction_input;
> +       data->gpiochip.direction_output = ltc4306_gpio_direction_output;
> +       data->gpiochip.get = ltc4306_gpio_get;
> +       data->gpiochip.set = ltc4306_gpio_set;
> +       data->gpiochip.set_config = ltc4306_gpio_set_config;
> +       data->gpiochip.owner = THIS_MODULE;

Please implement .get_direction().
This is very helpful to userspace, have you tested to use tools/gpio/*
from the kernel? Like lsgpio?

Yours,
Linus Walleij