GPIO Character Device Userspace API (v1)¶

Warning

This API is obsoleted by GPIO Character Device Userspace API (v2).

New developments should use the v2 API, and existing developments are encouraged to migrate as soon as possible, as this API will be removed in the future. The v2 API is a functional superset of the v1 API so any v1 call can be directly translated to a v2 equivalent.

This interface will continue to be maintained for the migration period, but new features will only be added to the new API.

First added in 4.8.

The API is based around three major objects, the Chip, the Line Handle, and the Line Event.

Where “line event” is used in this document it refers to the request that can monitor a line for edge events, not the edge events themselves.

Chip¶

The Chip represents a single GPIO chip and is exposed to userspace using device files of the form /dev/gpiochipX.

Each chip supports a number of GPIO lines, chip.lines. Lines on the chip are identified by an offset in the range from 0 to chip.lines - 1, i.e. [0,chip.lines).

Lines are requested from the chip using either GPIO_GET_LINEHANDLE_IOCTL and the resulting line handle is used to access the GPIO chip’s lines, or GPIO_GET_LINEEVENT_IOCTL and the resulting line event is used to monitor a GPIO line for edge events.

Within this documentation, the file descriptor returned by calling open() on the GPIO device file is referred to as chip_fd.

Operations¶

The following operations may be performed on the chip:

Line Handle¶

Line handles are created by GPIO_GET_LINEHANDLE_IOCTL and provide access to a set of requested lines. The line handle is exposed to userspace via the anonymous file descriptor returned in request.fd by GPIO_GET_LINEHANDLE_IOCTL.

Within this documentation, the line handle file descriptor is referred to as handle_fd.

Operations¶

The following operations may be performed on the line handle:

Line Event¶

Line events are created by GPIO_GET_LINEEVENT_IOCTL and provide access to a requested line. The line event is exposed to userspace via the anonymous file descriptor returned in request.fd by GPIO_GET_LINEEVENT_IOCTL.

Within this documentation, the line event file descriptor is referred to as event_fd.

Operations¶

The following operations may be performed on the line event:

Types¶

This section contains the structs that are referenced by the ABI v1.

The struct gpiochip_info is common to ABI v1 and v2.

struct gpioline_info¶: Information about a certain GPIO line

Definition:

struct gpioline_info {
    __u32 line_offset;
    __u32 flags;
    char name[GPIO_MAX_NAME_SIZE];
    char consumer[GPIO_MAX_NAME_SIZE];
};

Members

line_offset: the local offset on this GPIO device, fill this in when requesting the line information from the kernel
flags: various flags for this line
name: the name of this GPIO line, such as the output pin of the line on the chip, a rail or a pin header name on a board, as specified by the gpio chip, may be empty (i.e. name[0] == ‘0’)
consumer: a functional name for the consumer of this GPIO line as set by whatever is using it, will be empty if there is no current user but may also be empty if the consumer doesn’t set this up

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_info instead.

struct gpioline_info_changed¶: Information about a change in status of a GPIO line

Definition:

struct gpioline_info_changed {
    struct gpioline_info info;
    __u64 timestamp;
    __u32 event_type;
    __u32 padding[5];
};

Members

info: updated line information
timestamp: estimate of time of status change occurrence, in nanoseconds
event_type: one of GPIOLINE_CHANGED_REQUESTED, GPIOLINE_CHANGED_RELEASED and GPIOLINE_CHANGED_CONFIG
padding: reserved for future use

Description

The struct gpioline_info embedded here has 32-bit alignment on its own, but it works fine with 64-bit alignment too. With its 72 byte size, we can guarantee there are no implicit holes between it and subsequent members. The 20-byte padding at the end makes sure we don’t add any implicit padding at the end of the structure on 64-bit architectures.

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_info_changed instead.

struct gpiohandle_request¶: Information about a GPIO handle request

Definition:

struct gpiohandle_request {
    __u32 lineoffsets[GPIOHANDLES_MAX];
    __u32 flags;
    __u8 default_values[GPIOHANDLES_MAX];
    char consumer_label[GPIO_MAX_NAME_SIZE];
    __u32 lines;
    int fd;
};

Members

lineoffsets: an array of desired lines, specified by offset index for the associated GPIO device
flags: desired flags for the desired GPIO lines, such as GPIOHANDLE_REQUEST_OUTPUT, GPIOHANDLE_REQUEST_ACTIVE_LOW etc, added together. Note that even if multiple lines are requested, the same flags must be applicable to all of them, if you want lines with individual flags set, request them one by one. It is possible to select a batch of input or output lines, but they must all have the same characteristics, i.e. all inputs or all outputs, all active low etc
default_values: if the GPIOHANDLE_REQUEST_OUTPUT is set for a requested line, this specifies the default output value, should be 0 (inactive) or 1 (active). Anything other than 0 or 1 will be interpreted as active.
consumer_label: a desired consumer label for the selected GPIO line(s) such as “my-bitbanged-relay”
lines: number of lines requested in this request, i.e. the number of valid fields in the above arrays, set to 1 to request a single line
fd: after a successful GPIO_GET_LINEHANDLE_IOCTL operation, contains a valid anonymous file descriptor representing the request

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_request instead.

struct gpiohandle_config¶: Configuration for a GPIO handle request

Definition:

struct gpiohandle_config {
    __u32 flags;
    __u8 default_values[GPIOHANDLES_MAX];
    __u32 padding[4];
};

Members

flags: updated flags for the requested GPIO lines, such as GPIOHANDLE_REQUEST_OUTPUT, GPIOHANDLE_REQUEST_ACTIVE_LOW etc, added together
default_values: if the GPIOHANDLE_REQUEST_OUTPUT is set in flags, this specifies the default output value, should be 0 (inactive) or 1 (active). Anything other than 0 or 1 will be interpreted as active.
padding: reserved for future use and should be zero filled

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_config instead.

struct gpiohandle_data¶: Information of values on a GPIO handle

Definition:

struct gpiohandle_data {
    __u8 values[GPIOHANDLES_MAX];
};

Members

values: when getting the state of lines this contains the current state of a line, when setting the state of lines these should contain the desired target state. States are 0 (inactive) or 1 (active). When setting, anything other than 0 or 1 will be interpreted as active.

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_values instead.

struct gpioevent_request¶: Information about a GPIO event request

Definition:

struct gpioevent_request {
    __u32 lineoffset;
    __u32 handleflags;
    __u32 eventflags;
    char consumer_label[GPIO_MAX_NAME_SIZE];
    int fd;
};

Members

lineoffset: the desired line to subscribe to events from, specified by offset index for the associated GPIO device
handleflags: desired handle flags for the desired GPIO line, such as GPIOHANDLE_REQUEST_ACTIVE_LOW or GPIOHANDLE_REQUEST_OPEN_DRAIN
eventflags: desired flags for the desired GPIO event line, such as GPIOEVENT_REQUEST_RISING_EDGE or GPIOEVENT_REQUEST_FALLING_EDGE
consumer_label: a desired consumer label for the selected GPIO line(s) such as “my-listener”
fd: after a successful GPIO_GET_LINEEVENT_IOCTL operation, contains a valid anonymous file descriptor representing the request

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_request instead.

struct gpioevent_data¶: The actual event being pushed to userspace

Definition:

struct gpioevent_data {
    __u64 timestamp;
    __u32 id;
};

Members

timestamp: best estimate of time of event occurrence, in nanoseconds
id: event identifier, one of GPIOEVENT_EVENT_RISING_EDGE or GPIOEVENT_EVENT_FALLING_EDGE

Note

This struct is part of ABI v1 and is deprecated. Use ABI v2 and struct gpio_v2_line_event instead.