gpio: userspace ABI for reading GPIO line events

This adds an ABI for listening to events on GPIO lines.
The mechanism returns an anonymous file handle to a request
to listen to a specific offset on a specific gpiochip.
To fetch the stream of events from the file handle, userspace
simply reads an event.

- Events can be requested with the same flags as ordinary
  handles, i.e. open drain or open source. An ioctl() call
  GPIO_GET_LINEEVENT_IOCTL is issued indicating the desired
  line.

- Events can be requested for falling edge events, rising
  edge events, or both.

- All events are timestamped using the kernel real time
  nanosecond timestamp (the same as is used by IIO).

- The supplied consumer label will appear in "lsgpio"
  listings of the lines, and in /proc/interrupts as the
  mechanism will request an interrupt from the gpio chip.

- Events are not supported on gpiochips that do not serve
  interrupts (no legal .to_irq() call). The event interrupt
  is threaded to avoid any realtime problems.

- It is possible to also directly read the current value
  of the registered GPIO line by issuing the same
  GPIOHANDLE_GET_LINE_VALUES_IOCTL as used by the
  line handles. Setting the value is not supported: we
  do not listen to events on output lines.

This ABI is strongly influenced by Industrial I/O and surpasses
the old sysfs ABI by providing proper precision timestamps,
making it possible to set flags like open drain, and put
consumer names on the GPIO lines.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Linus Walleij 2016-06-02 11:30:15 +02:00
parent 2a144dd091
commit 61f922db72
2 changed files with 347 additions and 5 deletions

View File

@ -22,6 +22,9 @@
#include <linux/uaccess.h>
#include <linux/compat.h>
#include <linux/anon_inodes.h>
#include <linux/kfifo.h>
#include <linux/poll.h>
#include <linux/timekeeping.h>
#include <uapi/linux/gpio.h>
#include "gpiolib.h"
@ -501,6 +504,299 @@ out_free_lh:
return ret;
}
/*
* GPIO line event management
*/
/**
* struct lineevent_state - contains the state of a userspace event
* @gdev: the GPIO device the event pertains to
* @label: consumer label used to tag descriptors
* @desc: the GPIO descriptor held by this event
* @eflags: the event flags this line was requested with
* @irq: the interrupt that trigger in response to events on this GPIO
* @wait: wait queue that handles blocking reads of events
* @events: KFIFO for the GPIO events
* @read_lock: mutex lock to protect reads from colliding with adding
* new events to the FIFO
*/
struct lineevent_state {
struct gpio_device *gdev;
const char *label;
struct gpio_desc *desc;
u32 eflags;
int irq;
wait_queue_head_t wait;
DECLARE_KFIFO(events, struct gpioevent_data, 16);
struct mutex read_lock;
};
static unsigned int lineevent_poll(struct file *filep,
struct poll_table_struct *wait)
{
struct lineevent_state *le = filep->private_data;
unsigned int events = 0;
poll_wait(filep, &le->wait, wait);
if (!kfifo_is_empty(&le->events))
events = POLLIN | POLLRDNORM;
return events;
}
static ssize_t lineevent_read(struct file *filep,
char __user *buf,
size_t count,
loff_t *f_ps)
{
struct lineevent_state *le = filep->private_data;
unsigned int copied;
int ret;
if (count < sizeof(struct gpioevent_data))
return -EINVAL;
do {
if (kfifo_is_empty(&le->events)) {
if (filep->f_flags & O_NONBLOCK)
return -EAGAIN;
ret = wait_event_interruptible(le->wait,
!kfifo_is_empty(&le->events));
if (ret)
return ret;
}
if (mutex_lock_interruptible(&le->read_lock))
return -ERESTARTSYS;
ret = kfifo_to_user(&le->events, buf, count, &copied);
mutex_unlock(&le->read_lock);
if (ret)
return ret;
/*
* If we couldn't read anything from the fifo (a different
* thread might have been faster) we either return -EAGAIN if
* the file descriptor is non-blocking, otherwise we go back to
* sleep and wait for more data to arrive.
*/
if (copied == 0 && (filep->f_flags & O_NONBLOCK))
return -EAGAIN;
} while (copied == 0);
return copied;
}
static int lineevent_release(struct inode *inode, struct file *filep)
{
struct lineevent_state *le = filep->private_data;
struct gpio_device *gdev = le->gdev;
free_irq(le->irq, le);
gpiod_free(le->desc);
kfree(le->label);
kfree(le);
put_device(&gdev->dev);
return 0;
}
static long lineevent_ioctl(struct file *filep, unsigned int cmd,
unsigned long arg)
{
struct lineevent_state *le = filep->private_data;
void __user *ip = (void __user *)arg;
struct gpiohandle_data ghd;
/*
* We can get the value for an event line but not set it,
* because it is input by definition.
*/
if (cmd == GPIOHANDLE_GET_LINE_VALUES_IOCTL) {
int val;
val = gpiod_get_value_cansleep(le->desc);
if (val < 0)
return val;
ghd.values[0] = val;
if (copy_to_user(ip, &ghd, sizeof(ghd)))
return -EFAULT;
return 0;
}
return -EINVAL;
}
#ifdef CONFIG_COMPAT
static long lineevent_ioctl_compat(struct file *filep, unsigned int cmd,
unsigned long arg)
{
return lineevent_ioctl(filep, cmd, (unsigned long)compat_ptr(arg));
}
#endif
static const struct file_operations lineevent_fileops = {
.release = lineevent_release,
.read = lineevent_read,
.poll = lineevent_poll,
.owner = THIS_MODULE,
.llseek = noop_llseek,
.unlocked_ioctl = lineevent_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = lineevent_ioctl_compat,
#endif
};
irqreturn_t lineevent_irq_thread(int irq, void *p)
{
struct lineevent_state *le = p;
struct gpioevent_data ge;
int ret;
ge.timestamp = ktime_get_real_ns();
if (le->eflags & GPIOEVENT_REQUEST_BOTH_EDGES) {
int level = gpiod_get_value_cansleep(le->desc);
if (level)
/* Emit low-to-high event */
ge.id = GPIOEVENT_EVENT_RISING_EDGE;
else
/* Emit high-to-low event */
ge.id = GPIOEVENT_EVENT_FALLING_EDGE;
} else if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE) {
/* Emit low-to-high event */
ge.id = GPIOEVENT_EVENT_RISING_EDGE;
} else if (le->eflags & GPIOEVENT_REQUEST_FALLING_EDGE) {
/* Emit high-to-low event */
ge.id = GPIOEVENT_EVENT_FALLING_EDGE;
}
ret = kfifo_put(&le->events, ge);
if (ret != 0)
wake_up_poll(&le->wait, POLLIN);
return IRQ_HANDLED;
}
static int lineevent_create(struct gpio_device *gdev, void __user *ip)
{
struct gpioevent_request eventreq;
struct lineevent_state *le;
struct gpio_desc *desc;
u32 offset;
u32 lflags;
u32 eflags;
int fd;
int ret;
int irqflags = 0;
if (copy_from_user(&eventreq, ip, sizeof(eventreq)))
return -EFAULT;
le = kzalloc(sizeof(*le), GFP_KERNEL);
if (!le)
return -ENOMEM;
le->gdev = gdev;
get_device(&gdev->dev);
/* Make sure this is terminated */
eventreq.consumer_label[sizeof(eventreq.consumer_label)-1] = '\0';
if (strlen(eventreq.consumer_label)) {
le->label = kstrdup(eventreq.consumer_label,
GFP_KERNEL);
if (!le->label) {
ret = -ENOMEM;
goto out_free_le;
}
}
offset = eventreq.lineoffset;
lflags = eventreq.handleflags;
eflags = eventreq.eventflags;
/* This is just wrong: we don't look for events on output lines */
if (lflags & GPIOHANDLE_REQUEST_OUTPUT) {
ret = -EINVAL;
goto out_free_label;
}
desc = &gdev->descs[offset];
ret = gpiod_request(desc, le->label);
if (ret)
goto out_free_desc;
le->desc = desc;
le->eflags = eflags;
if (lflags & GPIOHANDLE_REQUEST_ACTIVE_LOW)
set_bit(FLAG_ACTIVE_LOW, &desc->flags);
if (lflags & GPIOHANDLE_REQUEST_OPEN_DRAIN)
set_bit(FLAG_OPEN_DRAIN, &desc->flags);
if (lflags & GPIOHANDLE_REQUEST_OPEN_SOURCE)
set_bit(FLAG_OPEN_SOURCE, &desc->flags);
ret = gpiod_direction_input(desc);
if (ret)
goto out_free_desc;
le->irq = gpiod_to_irq(desc);
if (le->irq <= 0) {
ret = -ENODEV;
goto out_free_desc;
}
if (eflags & GPIOEVENT_REQUEST_RISING_EDGE)
irqflags |= IRQF_TRIGGER_RISING;
if (eflags & GPIOEVENT_REQUEST_FALLING_EDGE)
irqflags |= IRQF_TRIGGER_FALLING;
irqflags |= IRQF_ONESHOT;
irqflags |= IRQF_SHARED;
INIT_KFIFO(le->events);
init_waitqueue_head(&le->wait);
mutex_init(&le->read_lock);
/* Request a thread to read the events */
ret = request_threaded_irq(le->irq,
NULL,
lineevent_irq_thread,
irqflags,
le->label,
le);
if (ret)
goto out_free_desc;
fd = anon_inode_getfd("gpio-event",
&lineevent_fileops,
le,
O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = fd;
goto out_free_irq;
}
eventreq.fd = fd;
if (copy_to_user(ip, &eventreq, sizeof(eventreq)))
return -EFAULT;
return 0;
out_free_irq:
free_irq(le->irq, le);
out_free_desc:
gpiod_free(le->desc);
out_free_label:
kfree(le->label);
out_free_le:
kfree(le);
put_device(&gdev->dev);
return ret;
}
/**
* gpio_ioctl() - ioctl handler for the GPIO chardev
*/
@ -578,6 +874,8 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
return 0;
} else if (cmd == GPIO_GET_LINEHANDLE_IOCTL) {
return linehandle_create(gdev, ip);
} else if (cmd == GPIO_GET_LINEEVENT_IOCTL) {
return lineevent_create(gdev, ip);
}
return -EINVAL;
}

View File

@ -55,7 +55,7 @@ struct gpioline_info {
/* Maximum number of requested handles */
#define GPIOHANDLES_MAX 64
/* Request flags */
/* Linerequest flags */
#define GPIOHANDLE_REQUEST_INPUT (1UL << 0)
#define GPIOHANDLE_REQUEST_OUTPUT (1UL << 1)
#define GPIOHANDLE_REQUEST_ACTIVE_LOW (1UL << 2)
@ -93,10 +93,6 @@ struct gpiohandle_request {
int fd;
};
#define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
#define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
#define GPIO_GET_LINEHANDLE_IOCTL _IOWR(0xB4, 0x03, struct gpiohandle_request)
/**
* struct gpiohandle_data - Information of values on a GPIO handle
* @values: when getting the state of lines this contains the current
@ -110,4 +106,52 @@ struct gpiohandle_data {
#define GPIOHANDLE_GET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x08, struct gpiohandle_data)
#define GPIOHANDLE_SET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x09, struct gpiohandle_data)
/* Eventrequest flags */
#define GPIOEVENT_REQUEST_RISING_EDGE (1UL << 0)
#define GPIOEVENT_REQUEST_FALLING_EDGE (1UL << 1)
#define GPIOEVENT_REQUEST_BOTH_EDGES ((1UL << 0) | (1UL << 1))
/**
* struct gpioevent_request - Information about a GPIO event request
* @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: if successful this field will contain a valid anonymous file handle
* after a GPIO_GET_LINEEVENT_IOCTL operation, zero or negative value
* means error
*/
struct gpioevent_request {
__u32 lineoffset;
__u32 handleflags;
__u32 eventflags;
char consumer_label[32];
int fd;
};
/**
* GPIO event types
*/
#define GPIOEVENT_EVENT_RISING_EDGE 0x01
#define GPIOEVENT_EVENT_FALLING_EDGE 0x02
/**
* struct gpioevent_data - The actual event being pushed to userspace
* @timestamp: best estimate of time of event occurrence, in nanoseconds
* @id: event identifier
*/
struct gpioevent_data {
__u64 timestamp;
__u32 id;
};
#define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
#define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
#define GPIO_GET_LINEHANDLE_IOCTL _IOWR(0xB4, 0x03, struct gpiohandle_request)
#define GPIO_GET_LINEEVENT_IOCTL _IOWR(0xB4, 0x04, struct gpioevent_request)
#endif /* _UAPI_GPIO_H_ */