[v5,1/2] gpio: add GPIO hogging mechanism

Based on Boris Brezillion's work this is a reworked patch
of his initial GPIO hogging mechanism.
This patch provides a way to initially configure specific GPIO
when the GPIO controller is probed.

The actual DT scanning to collect the GPIO specific data is performed
as part of gpiochip_add().

The purpose of this is to allow specific GPIOs to be configured
without any driver specific code.
This is particularly useful because board design are getting
increasingly complex and given SoC pins can now have more
than 10 mux values, a lot of connections are now dependent on
external IO muxes to switch various modes.

Specific drivers should not necessarily need to be aware of
what accounts to a specific board implementation. This board level
"description" should be best kept as part of the dts file.

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
---
 drivers/gpio/gpiolib-of.c | 118 ++++++++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib.c    | 128 ++++++++++++++++++++++++++++++++++++++--------
 drivers/gpio/gpiolib.h    |   3 ++
 3 files changed, 229 insertions(+), 20 deletions(-)

On Fri, Dec 19, 2014 at 9:07 PM, Benoit Parrot <bparrot@ti.com> wrote:

> Based on Boris Brezillion's work this is a reworked patch
> of his initial GPIO hogging mechanism.
> This patch provides a way to initially configure specific GPIO
> when the GPIO controller is probed.
>
> The actual DT scanning to collect the GPIO specific data is performed
> as part of gpiochip_add().
>
> The purpose of this is to allow specific GPIOs to be configured
> without any driver specific code.
> This is particularly useful because board design are getting
> increasingly complex and given SoC pins can now have more
> than 10 mux values, a lot of connections are now dependent on
> external IO muxes to switch various modes.
>
> Specific drivers should not necessarily need to be aware of
> what accounts to a specific board implementation. This board level
> "description" should be best kept as part of the dts file.
>
> Signed-off-by: Benoit Parrot <bparrot@ti.com>
> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

(...)
>  /**
> + * of_get_gpio_hog() - Get a GPIO hog descriptor, names and flags for GPIO API
> + * @np:                device node to get GPIO from
> + * @name:      GPIO line name
> + * @flags:     a flags pointer to fill in

kerneldoc is unsynchronized, document both flags.

> + *
> + * Returns GPIO descriptor to use with Linux GPIO API, or one of the errno
> + * value on the error condition.
> + */
> +

No newline after kerneldoc. What is lflags and dflags?

> +static struct gpio_desc *of_get_gpio_hog(struct device_node *np,
> +                                 const char **name,
> +                                 enum gpio_lookup_flags *lflags,
> +                                 enum gpiod_flags *dflags)
> +{
> +       struct device_node *chip_np;
> +       enum of_gpio_flags xlate_flags;
> +       struct gpio_desc *desc;
> +       const char *dir_val;
> +       struct gg_data gg_data = {
> +               .flags = &xlate_flags,
> +       };
> +       u32 tmp;
> +       int i, ret;
> +
> +       chip_np = np->parent;
> +       if (!chip_np)
> +               return ERR_PTR(-EINVAL);
> +
> +       xlate_flags = 0;
> +       *lflags = 0;
> +       *dflags = 0;
> +
> +       ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);
> +       if (ret)
> +               return ERR_PTR(ret);
> +       if (tmp > MAX_PHANDLE_ARGS)
> +               return ERR_PTR(-EINVAL);
> +       gg_data.gpiospec.args_count = tmp;
> +       gg_data.gpiospec.np = chip_np;

Are we duplicating this code elsewhere? No need to
fix now, but space for refactor later on...

> +       for (i = 0; i < tmp; i++) {
> +               ret = of_property_read_u32_index(np, "gpios", i,
> +                                          &gg_data.gpiospec.args[i]);
> +               if (ret)
> +                       return ERR_PTR(ret);
> +       }
> +
> +       gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);
> +       if (!gg_data.out_gpio) {
> +               if (np->parent == np)
> +                       return ERR_PTR(-ENXIO);
> +               else
> +                       return ERR_PTR(-EPROBE_DEFER);

Is this really reasonable, as we know we're instantiating the only
gpio_chip this hog can be on?

> +       }
> +
> +       if (xlate_flags & OF_GPIO_ACTIVE_LOW)
> +               *lflags |= GPIO_ACTIVE_LOW;
> +
> +       if (of_property_read_string(np, "state", &dir_val)) {
> +               pr_warn("%s: GPIO:%d (%s): no hogging state specified, bailing out\n",
> +                        __func__, desc_to_gpio(gg_data.out_gpio), np->name);
> +               return ERR_PTR(-EINVAL);
> +       }
> +
> +       if (!strcmp(dir_val, "input"))
> +               *dflags |= GPIOD_IN;
> +       else if (!strcmp(dir_val, "output-low"))
> +               *dflags |= GPIOD_OUT_LOW;
> +       else if (!strcmp(dir_val, "output-high"))
> +               *dflags |= GPIOD_OUT_HIGH;
> +       else {
> +               pr_warn("%s: GPIO:%d (%s): invalid state '%s' requested, bailing out\n",
> +                        __func__, desc_to_gpio(gg_data.out_gpio),
> +                       np->name, dir_val);
> +               return ERR_PTR(-EINVAL);
> +       }

Hmmmm need to check the bindings first. I'm not yet sure I
like how we represent this.

> +       if (name && of_property_read_string(np, "line-name", name))
> +               *name = np->name;

I quite like this.

> +
> +       desc = gg_data.out_gpio;
> +
> +       return desc;
> +}
> +
> +/**
> + * of_gpiochip_scan_hogs - Scan gpio-controller and apply GPIO hog as requested
> + * @chip:      gpio chip to act on
> + *
> + * This is only used by of_gpiochip_add to request/set GPIO initial
> + * configuration.
> + */
> +static void of_gpiochip_scan_hogs(struct gpio_chip *chip)
> +{
> +       struct gpio_desc *desc = NULL;
> +       struct device_node *np;
> +       const char *name;
> +       enum gpio_lookup_flags lflags;
> +       enum gpiod_flags dflags;
> +
> +       for_each_child_of_node(chip->of_node, np) {
> +               if (!of_property_read_bool(np, "gpio-hog"))
> +                       continue;
> +
> +               desc = of_get_gpio_hog(np, &name, &lflags, &dflags);
> +               if (IS_ERR(desc))
> +                       continue;
> +
> +               if (gpiod_hog(desc, name, lflags, dflags))
> +                       continue;
> +       }
> +}
> +
> +/**
>   * of_gpio_simple_xlate - translate gpio_spec to the GPIO number and flags
>   * @gc:                pointer to the gpio_chip structure
>   * @np:                device node of the GPIO chip
> @@ -302,6 +418,8 @@ void of_gpiochip_add(struct gpio_chip *chip)
>
>         of_gpiochip_add_pin_range(chip);
>         of_node_get(chip->of_node);
> +
> +       of_gpiochip_scan_hogs(chip);
>  }
>
>  void of_gpiochip_remove(struct gpio_chip *chip)
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 487afe6..d79c265 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -313,6 +313,7 @@ EXPORT_SYMBOL_GPL(gpiochip_add);
>
>  /* Forward-declaration */
>  static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip);
> +static void gpiochip_free_hogs(struct gpio_chip *chip);
>
>  /**
>   * gpiochip_remove() - unregister a gpio_chip
> @@ -331,6 +332,7 @@ void gpiochip_remove(struct gpio_chip *chip)
>
>         gpiochip_irqchip_remove(chip);
>         gpiochip_remove_pin_ranges(chip);
> +       gpiochip_free_hogs(chip);
>         of_gpiochip_remove(chip);
>
>         for (id = 0; id < chip->ngpio; id++) {
> @@ -864,6 +866,7 @@ static bool __gpiod_free(struct gpio_desc *desc)
>                 clear_bit(FLAG_REQUESTED, &desc->flags);
>                 clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
>                 clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
> +               clear_bit(FLAG_IS_HOGGED, &desc->flags);
>                 ret = true;
>         }
>
> @@ -1836,6 +1839,47 @@ struct gpio_desc *__must_check __gpiod_get_optional(struct device *dev,
>  }
>  EXPORT_SYMBOL_GPL(__gpiod_get_optional);
>
> +
> +/**
> + * __gpiod_set_helper - helper function to configure a given GPIO
> + * @desc:      gpio whose value will be assigned
> + * @con_id:    function within the GPIO consumer
> + * @lflags:    gpio_lookup_flags - returned from of_find_gpio() or
> + *             of_get_gpio_hog()
> + * @dflags:    gpiod_flags - optional GPIO initialization flags
> + *
> + * Return 0 on success, -ENOENT if no GPIO has been assigned to the
> + * requested function and/or index, or another IS_ERR() code if an error
> + * occurred while trying to acquire the GPIO.
> + */
> +static int __gpiod_set_helper(struct gpio_desc *desc, const char *con_id,
> +               unsigned long lflags, enum gpiod_flags dflags)

This function has no sensible name.

Skip the arbitrary __ prefix and give it a descriptive name
like "gpiod_configure_flags" or something.

> +{
> +       int status;
> +
> +       if (lflags & GPIO_ACTIVE_LOW)
> +               set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> +       if (lflags & GPIO_OPEN_DRAIN)
> +               set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> +       if (lflags & GPIO_OPEN_SOURCE)
> +               set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> +
> +       /* No particular flag request, return here... */
> +       if (!(dflags & GPIOD_FLAGS_BIT_DIR_SET)) {
> +               pr_debug("no flags found for %s\n", con_id);
> +               return 0;
> +       }
> +
> +       /* Process flags */
> +       if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
> +               status = gpiod_direction_output(desc,
> +                                             dflags & GPIOD_FLAGS_BIT_DIR_VAL);
> +       else
> +               status = gpiod_direction_input(desc);
> +
> +       return status;
> +}
> +
>  /**
>   * gpiod_get_index - obtain a GPIO from a multi-index GPIO function
>   * @dev:       GPIO consumer, can be NULL for system-global GPIOs
> @@ -1885,30 +1929,12 @@ struct gpio_desc *__must_check __gpiod_get_index(struct device *dev,
>         }
>
>         status = gpiod_request(desc, con_id);
> -
>         if (status < 0)
>                 return ERR_PTR(status);
>
> -       if (lookupflags & GPIO_ACTIVE_LOW)
> -               set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> -       if (lookupflags & GPIO_OPEN_DRAIN)
> -               set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> -       if (lookupflags & GPIO_OPEN_SOURCE)
> -               set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> -
> -       /* No particular flag request, return here... */
> -       if (!(flags & GPIOD_FLAGS_BIT_DIR_SET))
> -               return desc;
> -
> -       /* Process flags */
> -       if (flags & GPIOD_FLAGS_BIT_DIR_OUT)
> -               status = gpiod_direction_output(desc,
> -                                             flags & GPIOD_FLAGS_BIT_DIR_VAL);
> -       else
> -               status = gpiod_direction_input(desc);
> -
> +       status = __gpiod_set_helper(desc, con_id, lookupflags, flags);
>         if (status < 0) {
> -               dev_dbg(dev, "setup of GPIO %s failed\n", con_id);
> +               pr_debug("setup of GPIO %s failed\n", con_id);
>                 gpiod_put(desc);
>                 return ERR_PTR(status);
>         }
> @@ -2002,6 +2028,68 @@ struct gpio_desc *__must_check __gpiod_get_index_optional(struct device *dev,
>  EXPORT_SYMBOL_GPL(__gpiod_get_index_optional);
>
>  /**
> + * gpiod_hog - Hog the specified GPIO desc given the provided flags
> + * @desc:      gpio whose value will be assigned
> + * @name:      gpio line name
> + * @lflags:    gpio_lookup_flags - returned from of_find_gpio() or
> + *             of_get_gpio_hog()
> + * @dflags:    gpiod_flags - optional GPIO initialization flags
> + *
> + */
> +int gpiod_hog(struct gpio_desc *desc, const char *name,
> +             unsigned long lflags, enum gpiod_flags dflags)
> +{
> +       struct gpio_chip *chip;
> +       struct gpio_desc *local_desc;
> +       int hwnum;
> +       int status;
> +
> +       chip = gpiod_to_chip(desc);
> +       hwnum = gpio_chip_hwgpio(desc);
> +
> +       local_desc = gpiochip_request_own_desc(chip, hwnum, name);
> +       if (IS_ERR(local_desc)) {
> +               pr_debug("requesting own GPIO %s failed\n", name);
> +               return PTR_ERR(local_desc);
> +       }
> +
> +       status = __gpiod_set_helper(desc, name, lflags, dflags);
> +       if (status < 0) {
> +               pr_debug("setup of GPIO %s failed\n", name);
> +               gpiochip_free_own_desc(desc);
> +               return status;
> +       }
> +
> +       /* Mark GPIO as hogged so it can be identified and removed later */
> +       set_bit(FLAG_IS_HOGGED, &desc->flags);
> +
> +       pr_debug("%s: GPIO:%d (%s) as %s%s\n", __func__,

Convert to pr_info(), as this *should* be printed to console, skip printing
__func__ please.

Modify string to "GPIO line %d (%s) hogged as %s%s\n"

> +               desc_to_gpio(desc), name,
> +               (dflags&GPIOD_FLAGS_BIT_DIR_OUT) ? "output" : "input",
> +               (dflags&GPIOD_FLAGS_BIT_DIR_OUT) ?
> +                 (dflags&GPIOD_FLAGS_BIT_DIR_VAL) ? "/high" : "/low":"");
> +
> +       return 0;
> +}
> +
> +/**
> + * gpiochip_free_hogs - Scan gpio-controller chip and release GPIO hog
> + * @chip:      gpio chip to act on
> + *
> + * This is only used by of_gpiochip_remove to free hogged gpios
> + *

Skip this comment newline.

Overall the changes to gpiolib.c looks very nice.

Yours,
Linus Walleij
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