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

Linus Walleij
2025-02-18T10:28:07Z

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];
}

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>;

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

--
2.48.1