Re: [PATCH RTF 2/2] gpiolib: of: Handle threecell GPIO chips

Alex Elder
2025-02-24T14:43:06Z

On 2/18/25 4:28 AM, Linus Walleij wrote:
> When describing GPIO controllers in the device tree, the ambition
> of device tree to describe the hardware may require a three-cell
> scheme:
>
> gpios = <&gpio instance offset flags>;
>
> This implements support for this scheme in the gpiolib OF core.
>
> Drivers that want to handle multiple gpiochip instances from one
> OF node need to implement a callback similar to this to
> determine if a certain gpio chip is a pointer to the right
> instance (pseudo-code):
>
> struct my_gpio {
> struct gpio_chip gcs[MAX_CHIPS];
> };
>
> static bool my_of_node_instance_match(struct gpio_chip *gc
> unsigned int instance)
> {
> struct my_gpio *mg = gpiochip_get_data(gc);
>
> if (instance >= MAX_CHIPS)
> return false;
> return (gc == &mg->gcs[instance];

This is pseudocode, but either "(" not needed, or ")" missing.

> }
>
> probe() {
> struct my_gpio *mg;
> struct gpio_chip *gc;
> int i, ret;
>
> for (i = 0; i++; i < MAX_CHIPS) {
> gc = &mg->gcs[i];
> /* This tells gpiolib we have several instances per node */
> gc->of_gpio_n_cells = 3;
> gc->of_node_instance_match = my_of_node_instance_match;
> gc->base = -1;
> ...
>
> ret = devm_gpiochip_add_data(dev, gc, mg);
> if (ret)
> return ret;
> }
> }
>
> Rename the "simple" of_xlate function to "twocell" which is closer
> to what it actually does.
>
> In the device tree bindings, the provide node needs
> to specify #gpio-cells = <3>; where the first cell is the instance
> number:
>
> gpios = <&gpio instance offset flags>;
>
> Conversely ranges need to have four cells:
>
> gpio-ranges = <&pinctrl instance gpio_offset pin_offset count>;

I haven't looked for it, but is a DT binding update forthcoming?

> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

This looks good.

Reviewed-by: Alex Elder <elder@riscstar.com>

> ---
> drivers/gpio/gpiolib-of.c | 93 ++++++++++++++++++++++++++++++++++++++++-----
> include/linux/gpio/driver.h | 24 +++++++++++-
> 2 files changed, 106 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> index 86405218f4e2ddc951a1a9d168e886400652bf60..614590a5bcd10e5605ecb66ebd956250e4ea1fd8 100644
> --- a/drivers/gpio/gpiolib-of.c
> +++ b/drivers/gpio/gpiolib-of.c
> @@ -929,7 +929,7 @@ struct notifier_block gpio_of_notifier = {
> #endif /* CONFIG_OF_DYNAMIC */
>
> /**
> - * of_gpio_simple_xlate - translate gpiospec to the GPIO number and flags
> + * of_gpio_twocell_xlate - translate twocell gpiospec to the GPIO number and flags
> * @gc: pointer to the gpio_chip structure
> * @gpiospec: GPIO specifier as found in the device tree
> * @flags: a flags pointer to fill in
> @@ -941,9 +941,9 @@ struct notifier_block gpio_of_notifier = {
> * Returns:
> * GPIO number (>= 0) on success, negative errno on failure.
> */
> -static int of_gpio_simple_xlate(struct gpio_chip *gc,
> - const struct of_phandle_args *gpiospec,
> - u32 *flags)
> +static int of_gpio_twocell_xlate(struct gpio_chip *gc,
> + const struct of_phandle_args *gpiospec,
> + u32 *flags)
> {
> /*
> * We're discouraging gpio_cells < 2, since that way you'll have to
> @@ -968,6 +968,49 @@ static int of_gpio_simple_xlate(struct gpio_chip *gc,
> return gpiospec->args[0];
> }
>
> +/**
> + * of_gpio_threecell_xlate - translate threecell gpiospec to the GPIO number and flags
> + * @gc: pointer to the gpio_chip structure
> + * @gpiospec: GPIO specifier as found in the device tree
> + * @flags: a flags pointer to fill in
> + *
> + * This is simple translation function, suitable for the most 1:n mapped
> + * GPIO chips, i.e. several GPIO chip instances from one device tree node.
> + * In this case the following binding is implied:
> + *
> + * foo-gpios = <&gpio instance offset flags>;
> + *
> + * Returns:
> + * GPIO number (>= 0) on success, negative errno on failure.
> + */
> +static int of_gpio_threecell_xlate(struct gpio_chip *gc,
> + const struct of_phandle_args *gpiospec,
> + u32 *flags)
> +{
> + if (gc->of_gpio_n_cells != 3) {
> + WARN_ON(1);
> + return -EINVAL;
> + }
> +
> + if (WARN_ON(gpiospec->args_count != 3))
> + return -EINVAL;
> +
> + /*
> + * Check chip instance number, the driver responds with true if
> + * this is the chip we are looking for.
> + */
> + if (!gc->of_node_instance_match(gc, gpiospec->args[0]))
> + return -EINVAL;
> +
> + if (gpiospec->args[1] >= gc->ngpio)
> + return -EINVAL;
> +
> + if (flags)
> + *flags = gpiospec->args[2];
> +
> + return gpiospec->args[1];
> +}
> +
> #if IS_ENABLED(CONFIG_OF_GPIO_MM_GPIOCHIP)
> #include <linux/gpio/legacy-of-mm-gpiochip.h>
> /**
> @@ -1068,7 +1111,15 @@ static int of_gpiochip_add_pin_range(struct gpio_chip *chip)
> has_group_names = of_property_present(np, group_names_propname);
>
> for (;; index++) {
> - ret = of_parse_phandle_with_fixed_args(np, "gpio-ranges", 3,
> + /*
> + * Ordinary phandles contain 2-3 cells:
> + * gpios = <&gpio [instance] offset flags>;
> + * Ranges always contain one more cell:
> + * gpio-ranges <&pinctrl [gpio_instance] gpio_offet pin_offet count>;
> + * This is why we parse chip->of_gpio_n_cells + 1 cells
> + */
> + ret = of_parse_phandle_with_fixed_args(np, "gpio-ranges",
> + chip->of_gpio_n_cells + 1,
> index, &pinspec);
> if (ret)
> break;
> @@ -1078,9 +1129,25 @@ static int of_gpiochip_add_pin_range(struct gpio_chip *chip)
> if (!pctldev)
> return -EPROBE_DEFER;
>
> - offset = pinspec.args[0];
> - pin = pinspec.args[1];
> - count = pinspec.args[2];
> + if (chip->of_gpio_n_cells == 3) {
> + /* First cell is the gpiochip instance number */
> + offset = pinspec.args[1];
> + pin = pinspec.args[2];
> + count = pinspec.args[3];
> + } else {
> + offset = pinspec.args[0];
> + pin = pinspec.args[1];
> + count = pinspec.args[2];
> + }
> +
> + /*
> + * With multiple GPIO chips per node, check that this chip is the
> + * right instance.
> + */
> + if (chip->of_node_instance_match &&
> + (chip->of_gpio_n_cells == 3) &&
> + !chip->of_node_instance_match(chip, pinspec.args[0]))
> + continue;
>
> /* Ignore ranges outside of this GPIO chip */
> if (offset >= (chip->offset + chip->ngpio))
> @@ -1170,8 +1237,14 @@ int of_gpiochip_add(struct gpio_chip *chip)
> return 0;
>
> if (!chip->of_xlate) {
> - chip->of_gpio_n_cells = 2;
> - chip->of_xlate = of_gpio_simple_xlate;
> + if (chip->of_gpio_n_cells == 3) {
> + if (!chip->of_node_instance_match)
> + return -EINVAL;
> + chip->of_xlate = of_gpio_threecell_xlate;
> + } else {
> + chip->of_gpio_n_cells = 2;
> + chip->of_xlate = of_gpio_twocell_xlate;
> + }
> }
>
> if (chip->of_gpio_n_cells > MAX_PHANDLE_ARGS)
> diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> index 2dd7cb9cc270a68ddedbcdd5d44e0d0f88dfa785..70a361f6aba06d4a11e5ca913ec79411d7a11b3c 100644
> --- a/include/linux/gpio/driver.h
> +++ b/include/linux/gpio/driver.h
> @@ -516,10 +516,32 @@ struct gpio_chip {
> /**
> * @of_gpio_n_cells:
> *
> - * Number of cells used to form the GPIO specifier.
> + * Number of cells used to form the GPIO specifier. The standard i 2

s/standard i /standard is /

> + * cells:
> + *
> + * gpios = <&gpio offset flags>;
> + *
> + * some complex GPIO controllers instantiate more than one chip per
> + * device tree node and have 3 cells:
> + *
> + * gpios = <&gpio instance offset flags>;
> + *
> + * Legacy GPIO controllers may even have 1 cell:
> + *
> + * gpios = <&gpio offset>;
> */
> unsigned int of_gpio_n_cells;
>
> + /**
> + * of_node_instance_match:
> + *
> + * Determine if a chip is the right instance. Must be implemented by
> + * any driver using more than one gpio_chip per device tree node.
> + * Returns true if gc is the instance indicated by i (which is the
> + * first cell in the phandles for GPIO lines and gpio-ranges).
> + */
> + bool (*of_node_instance_match)(struct gpio_chip *gc, unsigned int i);
> +
> /**
> * @of_xlate:
> *
>