223 lines
8.7 KiB
ReStructuredText
223 lines
8.7 KiB
ReStructuredText
=============
|
|
GPIO Mappings
|
|
=============
|
|
|
|
This document explains how GPIOs can be assigned to given devices and functions.
|
|
|
|
Note that it only applies to the new descriptor-based interface. For a
|
|
description of the deprecated integer-based GPIO interface please refer to
|
|
legacy.rst (actually, there is no real mapping possible with the old
|
|
interface; you just fetch an integer from somewhere and request the
|
|
corresponding GPIO).
|
|
|
|
All platforms can enable the GPIO library, but if the platform strictly
|
|
requires GPIO functionality to be present, it needs to select GPIOLIB from its
|
|
Kconfig. Then, how GPIOs are mapped depends on what the platform uses to
|
|
describe its hardware layout. Currently, mappings can be defined through device
|
|
tree, ACPI, and platform data.
|
|
|
|
Device Tree
|
|
-----------
|
|
GPIOs can easily be mapped to devices and functions in the device tree. The
|
|
exact way to do it depends on the GPIO controller providing the GPIOs, see the
|
|
device tree bindings for your controller.
|
|
|
|
GPIOs mappings are defined in the consumer device's node, in a property named
|
|
<function>-gpios, where <function> is the function the driver will request
|
|
through gpiod_get(). For example::
|
|
|
|
foo_device {
|
|
compatible = "acme,foo";
|
|
...
|
|
led-gpios = <&gpio 15 GPIO_ACTIVE_HIGH>, /* red */
|
|
<&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
|
|
<&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
|
|
|
|
power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
|
|
};
|
|
|
|
Properties named <function>-gpio are also considered valid and old bindings use
|
|
it but are only supported for compatibility reasons and should not be used for
|
|
newer bindings since it has been deprecated.
|
|
|
|
This property will make GPIOs 15, 16 and 17 available to the driver under the
|
|
"led" function, and GPIO 1 as the "power" GPIO::
|
|
|
|
struct gpio_desc *red, *green, *blue, *power;
|
|
|
|
red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
|
|
green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
|
|
blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
|
|
|
|
power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
|
|
|
|
The led GPIOs will be active high, while the power GPIO will be active low (i.e.
|
|
gpiod_is_active_low(power) will be true).
|
|
|
|
The second parameter of the gpiod_get() functions, the con_id string, has to be
|
|
the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically
|
|
looked up by the gpiod functions internally) used in the device tree. With above
|
|
"led-gpios" example, use the prefix without the "-" as con_id parameter: "led".
|
|
|
|
Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio")
|
|
with the string passed in con_id to get the resulting string
|
|
(``snprintf(... "%s-%s", con_id, gpio_suffixes[]``).
|
|
|
|
ACPI
|
|
----
|
|
ACPI also supports function names for GPIOs in a similar fashion to DT.
|
|
The above DT example can be converted to an equivalent ACPI description
|
|
with the help of _DSD (Device Specific Data), introduced in ACPI 5.1::
|
|
|
|
Device (FOO) {
|
|
Name (_CRS, ResourceTemplate () {
|
|
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
|
|
"\\_SB.GPI0", 0, ResourceConsumer) { 15 } // red
|
|
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
|
|
"\\_SB.GPI0", 0, ResourceConsumer) { 16 } // green
|
|
GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionOutputOnly,
|
|
"\\_SB.GPI0", 0, ResourceConsumer) { 17 } // blue
|
|
GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionOutputOnly,
|
|
"\\_SB.GPI0", 0, ResourceConsumer) { 1 } // power
|
|
})
|
|
|
|
Name (_DSD, Package () {
|
|
ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
|
|
Package () {
|
|
Package () {
|
|
"led-gpios",
|
|
Package () {
|
|
^FOO, 0, 0, 1,
|
|
^FOO, 1, 0, 1,
|
|
^FOO, 2, 0, 1,
|
|
}
|
|
},
|
|
Package () { "power-gpios", Package () { ^FOO, 3, 0, 0 } },
|
|
}
|
|
})
|
|
}
|
|
|
|
For more information about the ACPI GPIO bindings see
|
|
Documentation/firmware-guide/acpi/gpio-properties.rst.
|
|
|
|
Platform Data
|
|
-------------
|
|
Finally, GPIOs can be bound to devices and functions using platform data. Board
|
|
files that desire to do so need to include the following header::
|
|
|
|
#include <linux/gpio/machine.h>
|
|
|
|
GPIOs are mapped by the means of tables of lookups, containing instances of the
|
|
gpiod_lookup structure. Two macros are defined to help declaring such mappings::
|
|
|
|
GPIO_LOOKUP(key, chip_hwnum, con_id, flags)
|
|
GPIO_LOOKUP_IDX(key, chip_hwnum, con_id, idx, flags)
|
|
|
|
where
|
|
|
|
- key is either the label of the gpiod_chip instance providing the GPIO, or
|
|
the GPIO line name
|
|
- chip_hwnum is the hardware number of the GPIO within the chip, or U16_MAX
|
|
to indicate that key is a GPIO line name
|
|
- con_id is the name of the GPIO function from the device point of view. It
|
|
can be NULL, in which case it will match any function.
|
|
- idx is the index of the GPIO within the function.
|
|
- flags is defined to specify the following properties:
|
|
* GPIO_ACTIVE_HIGH - GPIO line is active high
|
|
* GPIO_ACTIVE_LOW - GPIO line is active low
|
|
* GPIO_OPEN_DRAIN - GPIO line is set up as open drain
|
|
* GPIO_OPEN_SOURCE - GPIO line is set up as open source
|
|
* GPIO_PERSISTENT - GPIO line is persistent during
|
|
suspend/resume and maintains its value
|
|
* GPIO_TRANSITORY - GPIO line is transitory and may loose its
|
|
electrical state during suspend/resume
|
|
|
|
In the future, these flags might be extended to support more properties.
|
|
|
|
Note that:
|
|
1. GPIO line names are not guaranteed to be globally unique, so the first
|
|
match found will be used.
|
|
2. GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
|
|
|
|
A lookup table can then be defined as follows, with an empty entry defining its
|
|
end. The 'dev_id' field of the table is the identifier of the device that will
|
|
make use of these GPIOs. It can be NULL, in which case it will be matched for
|
|
calls to gpiod_get() with a NULL device.
|
|
|
|
.. code-block:: c
|
|
|
|
struct gpiod_lookup_table gpios_table = {
|
|
.dev_id = "foo.0",
|
|
.table = {
|
|
GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
|
|
GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
|
|
GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
|
|
GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
|
|
{ },
|
|
},
|
|
};
|
|
|
|
And the table can be added by the board code as follows::
|
|
|
|
gpiod_add_lookup_table(&gpios_table);
|
|
|
|
The driver controlling "foo.0" will then be able to obtain its GPIOs as follows::
|
|
|
|
struct gpio_desc *red, *green, *blue, *power;
|
|
|
|
red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
|
|
green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
|
|
blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
|
|
|
|
power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
|
|
|
|
Since the "led" GPIOs are mapped as active-high, this example will switch their
|
|
signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped
|
|
as active-low, its actual signal will be 0 after this code. Contrary to the
|
|
legacy integer GPIO interface, the active-low property is handled during
|
|
mapping and is thus transparent to GPIO consumers.
|
|
|
|
A set of functions such as gpiod_set_value() is available to work with
|
|
the new descriptor-oriented interface.
|
|
|
|
Boards using platform data can also hog GPIO lines by defining GPIO hog tables.
|
|
|
|
.. code-block:: c
|
|
|
|
struct gpiod_hog gpio_hog_table[] = {
|
|
GPIO_HOG("gpio.0", 10, "foo", GPIO_ACTIVE_LOW, GPIOD_OUT_HIGH),
|
|
{ }
|
|
};
|
|
|
|
And the table can be added to the board code as follows::
|
|
|
|
gpiod_add_hogs(gpio_hog_table);
|
|
|
|
The line will be hogged as soon as the gpiochip is created or - in case the
|
|
chip was created earlier - when the hog table is registered.
|
|
|
|
Arrays of pins
|
|
--------------
|
|
In addition to requesting pins belonging to a function one by one, a device may
|
|
also request an array of pins assigned to the function. The way those pins are
|
|
mapped to the device determines if the array qualifies for fast bitmap
|
|
processing. If yes, a bitmap is passed over get/set array functions directly
|
|
between a caller and a respective .get/set_multiple() callback of a GPIO chip.
|
|
|
|
In order to qualify for fast bitmap processing, the array must meet the
|
|
following requirements:
|
|
|
|
- pin hardware number of array member 0 must also be 0,
|
|
- pin hardware numbers of consecutive array members which belong to the same
|
|
chip as member 0 does must also match their array indexes.
|
|
|
|
Otherwise fast bitmap processing path is not used in order to avoid consecutive
|
|
pins which belong to the same chip but are not in hardware order being processed
|
|
separately.
|
|
|
|
If the array applies for fast bitmap processing path, pins which belong to
|
|
different chips than member 0 does, as well as those with indexes different from
|
|
their hardware pin numbers, are excluded from the fast path, both input and
|
|
output. Moreover, open drain and open source pins are excluded from fast bitmap
|
|
output processing.
|