Re: [PATCH v2 2/2] gpio: max7317: Add gpio expander driver

[Bartosz Golaszewski <brgl@bgdev.pl>]

On Mon, Apr 3, 2023 at 1:41 PM Edmund Berenson
<edmund.berenson@emlix.com> wrote:
>
> Add driver for maxim MAX7317 SPI-Interfaced 10 Port
> GPIO Expander.
>
> v2: adjust driver to use regmap
>
> Co-developed-by: Lukasz Zemla <Lukasz.Zemla@woodward.com>
> Signed-off-by: Lukasz Zemla <Lukasz.Zemla@woodward.com>
> Signed-off-by: Edmund Berenson <edmund.berenson@emlix.com>
> ---
>  drivers/gpio/Kconfig        |  11 +++
>  drivers/gpio/Makefile       |   1 +
>  drivers/gpio/gpio-max7317.c | 161 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 173 insertions(+)
>  create mode 100644 drivers/gpio/gpio-max7317.c
>
> diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
> index 13be729710f2..109cf09d8c05 100644
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -1615,6 +1615,17 @@ config GPIO_MAX7301
>         help
>           GPIO driver for Maxim MAX7301 SPI-based GPIO expander.
>
> +config GPIO_MAX7317
> +       tristate "Maxim MAX7317 GPIO expander"
> +       select REGMAP_SPI
> +       help
> +         GPIO driver for Maxim MAX7317 SPI-based GPIO expander.
> +         The MAX7317 is a serial-interfaced gpio extender, with
> +         10 ports.
> +
> +         This driver can also be built as a module. If so, the module will be
> +         called gpio-max7317.
> +
>  config GPIO_MC33880
>         tristate "Freescale MC33880 high-side/low-side switch"
>         help
> diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
> index c048ba003367..8dce549bb6c5 100644
> --- a/drivers/gpio/Makefile
> +++ b/drivers/gpio/Makefile
> @@ -91,6 +91,7 @@ obj-$(CONFIG_GPIO_MAX7300)            += gpio-max7300.o
>  obj-$(CONFIG_GPIO_MAX7301)             += gpio-max7301.o
>  obj-$(CONFIG_GPIO_MAX730X)             += gpio-max730x.o
>  obj-$(CONFIG_GPIO_MAX732X)             += gpio-max732x.o
> +obj-$(CONFIG_GPIO_MAX7317)             += gpio-max7317.o
>  obj-$(CONFIG_GPIO_MAX77620)            += gpio-max77620.o
>  obj-$(CONFIG_GPIO_MAX77650)            += gpio-max77650.o
>  obj-$(CONFIG_GPIO_MB86S7X)             += gpio-mb86s7x.o
> diff --git a/drivers/gpio/gpio-max7317.c b/drivers/gpio/gpio-max7317.c
> new file mode 100644
> index 000000000000..65824efaad6c
> --- /dev/null
> +++ b/drivers/gpio/gpio-max7317.c
> @@ -0,0 +1,161 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2021, Lukasz Zemla, Woodward Inc.
> + */
> +
> +#include <linux/gpio.h>
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +#include <linux/spi/spi.h>
> +
> +#define MAX7317_PIN_NUMBER 10
> +#define REG_CODE_READ_PORTS_7_TO_0     ((u8)0x0E)
> +#define REG_CODE_READ_PORTS_9_TO_8     ((u8)0x0F)
> +
> +struct max7317 {

Please call it max7317_gpio or something similar.

> +       struct gpio_chip        chip;
> +       struct regmap           *regmap;
> +       int                     direction[MAX7317_PIN_NUMBER];

Don't use tabs in structs, it doesn't really add to readability in
small declarations.

> +};
> +
> +struct max7317_platform_data {
> +       unsigned int    gpio_base;
> +};
> +
> +static const struct regmap_config max7317_regmap_cfg =  {
> +       .reg_bits = 8,
> +       .val_bits = 8,
> +};
> +
> +static int max7317_get(struct gpio_chip *chip, unsigned int offset)
> +{
> +       struct max7317 *ts = gpiochip_get_data(chip);
> +       unsigned int val;
> +       int ret;
> +       u8 reg = (offset < 8) ? REG_CODE_READ_PORTS_7_TO_0 : REG_CODE_READ_PORTS_9_TO_8;
> +
> +       ret = regmap_read(ts->regmap, reg, &val);
> +       if (ret)
> +               return ret;
> +
> +       return val & BIT(offset % 8);
> +}
> +
> +/*
> + * After writing the register an additional read is performed in order for
> + * changes to take effect.
> + */
> +static void max7317_set(struct gpio_chip *chip, unsigned int offset, int value)
> +{
> +       struct max7317 *ts = gpiochip_get_data(chip);
> +
> +       if (regmap_write(ts->regmap, offset, value ? 1 : 0))
> +               dev_err(chip->parent, "Failed to set pin: %d\n", offset);
> +       max7317_get(chip, offset);

Don't you need to protect both the write and read operations from
concurrent access here?


> +}
> +
> +static int max7317_direction_input(struct gpio_chip *chip, unsigned int offset)
> +{
> +       struct max7317 *ts = gpiochip_get_data(chip);
> +
> +       max7317_set(chip, offset, 1);
> +       ts->direction[offset] = GPIO_LINE_DIRECTION_IN;
> +       return 0;
> +}
> +
> +static int max7317_direction_output(struct gpio_chip *chip, unsigned int offset,
> +                                   int value)
> +{
> +       struct max7317 *ts = gpiochip_get_data(chip);
> +
> +       ts->direction[offset] = GPIO_LINE_DIRECTION_OUT;
> +       return 0;
> +}
> +
> +static int max7317_get_direction(struct gpio_chip *chip, unsigned int offset)
> +{
> +       struct max7317 *ts = gpiochip_get_data(chip);
> +
> +       return ts->direction[offset];
> +}
> +
> +static int max7317_probe(struct spi_device *spi)
> +{
> +       struct max7317 *ts;
> +       struct device *dev;
> +       struct max7317_platform_data *pdata;

Where does this come from?

> +       int i;
> +
> +       ts = devm_kzalloc(&spi->dev, sizeof(struct max7317), GFP_KERNEL);
> +       if (!ts)
> +               return -ENOMEM;
> +       dev_set_drvdata(&spi->dev, ts);
> +
> +       pdata = dev_get_platdata(dev);
> +       if (pdata)
> +               ts->chip.base = pdata->gpio_base;

Don't encourage setting a hard-coded base via platform data. Please
use -1 unconditionally in new drivers.

> +       else
> +               ts->chip.base = -1;
> +
> +       ts->chip.label = dev_name(&spi->dev);
> +       ts->chip.direction_input = max7317_direction_input;
> +       ts->chip.get = max7317_get;
> +       ts->chip.direction_output = max7317_direction_output;
> +       ts->chip.set = max7317_set;
> +       ts->chip.get_direction = max7317_get_direction;
> +
> +       ts->chip.ngpio = MAX7317_PIN_NUMBER;
> +       ts->chip.can_sleep = true;
> +       ts->chip.parent = &spi->dev;
> +       ts->chip.owner = THIS_MODULE;
> +
> +       for (i = 0; i < MAX7317_PIN_NUMBER; i++)
> +               ts->direction[i] = GPIO_LINE_DIRECTION_IN;
> +
> +       ts->regmap = devm_regmap_init_spi(spi, &max7317_regmap_cfg);
> +       if (IS_ERR(ts->regmap))
> +               return PTR_ERR(ts->regmap);
> +
> +       return devm_gpiochip_add_data(&spi->dev, &ts->chip, ts);
> +}
> +
> +static void max7317_remove(struct spi_device *spi)
> +{
> +       struct max7317 *ts = dev_get_drvdata(&spi->dev);
> +
> +       if (!ts)
> +               return;
> +
> +       gpiochip_remove(&ts->chip);

This is clearly wrong - you registered the chip using
devm_gpiochip_add_data() precisely to avoid having to call
gpiochip_remove(). And checking for !it makes no sense either - you
should have set it yourself, which you didn't.

Bart

> +}
> +
> +static const struct spi_device_id max7317_id[] = {
> +       { "max7317", 0 },
> +       { }
> +};
> +MODULE_DEVICE_TABLE(spi, max7317_id);
> +
> +static const struct of_device_id max7317_dt_ids[] = {
> +       { .compatible = "maxim,max7317" },
> +       { }
> +};
> +MODULE_DEVICE_TABLE(of, max7317_dt_ids);
> +
> +static struct spi_driver max7317_driver = {
> +       .driver = {
> +               .name = "max7317",
> +               .of_match_table = max7317_dt_ids,
> +       },
> +       .probe = max7317_probe,
> +       .remove = max7317_remove,
> +       .id_table = max7317_id,
> +};
> +module_spi_driver(max7317_driver);
> +
> +MODULE_AUTHOR("Lukasz Zemla");
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("MAX7317 GPIO-Expander");
> --
> 2.39.2
>