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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>;
Reviewed-by: Alex Elder <elder@riscstar.com>
Tested-by: Yixun Lan <dlan@gentoo.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20250225-gpio-ranges-fourcell-v3-2-860382ba4713@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.