Commit d7c51b47 authored by Linus Walleij's avatar Linus Walleij

gpio: userspace ABI for reading/writing GPIO lines

This adds a userspace ABI for reading and writing GPIO lines.
The mechanism returns an anonymous file handle to a request
to read/write n offsets from a gpiochip. This file handle
in turn accepts two ioctl()s: one that reads and one that
writes values to the selected lines.

- Handles can be requested as input/output, active low,
  open drain, open source, however when you issue a request
  for n lines with GPIO_GET_LINEHANDLE_IOCTL, they must all
  have the same flags, i.e. all inputs or all outputs, all
  open drain etc. If a granular control of the flags for
  each line is desired, they need to be requested
  individually, not in a batch.

- The GPIOHANDLE_GET_LINE_VALUES_IOCTL read ioctl() can be
  issued also to output lines to verify that the hardware
  is in the expected state.

- It reads and writes up to GPIOHANDLES_MAX lines at once,
  utilizing the .set_multiple() call in the driver if
  possible, making the call efficient if several lines
  can be written with a single register update.

The limitation of GPIOHANDLES_MAX to 64 lines is done under
the assumption that we may expect hardware that can issue a
transaction updating 64 bits at an instant but unlikely
anything larger than that.

ChangeLog v2->v3:
- Use gpiod_get_value_cansleep() so we support also slowpath
  GPIO drivers.
- Fix up the UAPI docs kerneldoc.
- Allocate the anonymous fd last, so that the release
  function don't get called until that point of something
  fails. After this point, skip the errorpath.
ChangeLog v1->v2:
- Handle ioctl_compat() properly based on a similar patch
  to the other ioctl() handling code.
- Use _IOWR() as we pass pointers both in and out of the
  ioctl()
- Use kmalloc() and kfree() for the linehandled, do not
  try to be fancy with devm_* it doesn't work the way I
  thought.
- Fix const-correctness on the linehandle name field.
Acked-by: default avatarMichael Welling <mwelling@ieee.org>
Signed-off-by: Linus Walleij's avatarLinus Walleij <linus.walleij@linaro.org>
parent 747e42a1
...@@ -21,6 +21,7 @@ ...@@ -21,6 +21,7 @@
#include <linux/fs.h> #include <linux/fs.h>
#include <linux/uaccess.h> #include <linux/uaccess.h>
#include <linux/compat.h> #include <linux/compat.h>
#include <linux/anon_inodes.h>
#include <uapi/linux/gpio.h> #include <uapi/linux/gpio.h>
#include "gpiolib.h" #include "gpiolib.h"
...@@ -310,6 +311,196 @@ static int gpiochip_set_desc_names(struct gpio_chip *gc) ...@@ -310,6 +311,196 @@ static int gpiochip_set_desc_names(struct gpio_chip *gc)
return 0; return 0;
} }
/*
* GPIO line handle management
*/
/**
* struct linehandle_state - contains the state of a userspace handle
* @gdev: the GPIO device the handle pertains to
* @label: consumer label used to tag descriptors
* @descs: the GPIO descriptors held by this handle
* @numdescs: the number of descriptors held in the descs array
*/
struct linehandle_state {
struct gpio_device *gdev;
const char *label;
struct gpio_desc *descs[GPIOHANDLES_MAX];
u32 numdescs;
};
static long linehandle_ioctl(struct file *filep, unsigned int cmd,
unsigned long arg)
{
struct linehandle_state *lh = filep->private_data;
void __user *ip = (void __user *)arg;
struct gpiohandle_data ghd;
int i;
if (cmd == GPIOHANDLE_GET_LINE_VALUES_IOCTL) {
int val;
/* TODO: check if descriptors are really input */
for (i = 0; i < lh->numdescs; i++) {
val = gpiod_get_value_cansleep(lh->descs[i]);
if (val < 0)
return val;
ghd.values[i] = val;
}
if (copy_to_user(ip, &ghd, sizeof(ghd)))
return -EFAULT;
return 0;
} else if (cmd == GPIOHANDLE_SET_LINE_VALUES_IOCTL) {
int vals[GPIOHANDLES_MAX];
/* TODO: check if descriptors are really output */
if (copy_from_user(&ghd, ip, sizeof(ghd)))
return -EFAULT;
/* Clamp all values to [0,1] */
for (i = 0; i < lh->numdescs; i++)
vals[i] = !!ghd.values[i];
/* Reuse the array setting function */
gpiod_set_array_value_complex(false,
true,
lh->numdescs,
lh->descs,
vals);
return 0;
}
return -EINVAL;
}
#ifdef CONFIG_COMPAT
static long linehandle_ioctl_compat(struct file *filep, unsigned int cmd,
unsigned long arg)
{
return linehandle_ioctl(filep, cmd, (unsigned long)compat_ptr(arg));
}
#endif
static int linehandle_release(struct inode *inode, struct file *filep)
{
struct linehandle_state *lh = filep->private_data;
struct gpio_device *gdev = lh->gdev;
int i;
for (i = 0; i < lh->numdescs; i++)
gpiod_free(lh->descs[i]);
kfree(lh->label);
kfree(lh);
put_device(&gdev->dev);
return 0;
}
static const struct file_operations linehandle_fileops = {
.release = linehandle_release,
.owner = THIS_MODULE,
.llseek = noop_llseek,
.unlocked_ioctl = linehandle_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = linehandle_ioctl_compat,
#endif
};
static int linehandle_create(struct gpio_device *gdev, void __user *ip)
{
struct gpiohandle_request handlereq;
struct linehandle_state *lh;
int fd, i, ret;
if (copy_from_user(&handlereq, ip, sizeof(handlereq)))
return -EFAULT;
if ((handlereq.lines == 0) || (handlereq.lines > GPIOHANDLES_MAX))
return -EINVAL;
lh = kzalloc(sizeof(*lh), GFP_KERNEL);
if (!lh)
return -ENOMEM;
lh->gdev = gdev;
get_device(&gdev->dev);
/* Make sure this is terminated */
handlereq.consumer_label[sizeof(handlereq.consumer_label)-1] = '\0';
if (strlen(handlereq.consumer_label)) {
lh->label = kstrdup(handlereq.consumer_label,
GFP_KERNEL);
if (!lh->label) {
ret = -ENOMEM;
goto out_free_lh;
}
}
/* Request each GPIO */
for (i = 0; i < handlereq.lines; i++) {
u32 offset = handlereq.lineoffsets[i];
u32 lflags = handlereq.flags;
struct gpio_desc *desc;
desc = &gdev->descs[offset];
ret = gpiod_request(desc, lh->label);
if (ret)
goto out_free_descs;
lh->descs[i] = desc;
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);
/*
* Lines have to be requested explicitly for input
* or output, else the line will be treated "as is".
*/
if (lflags & GPIOHANDLE_REQUEST_OUTPUT) {
int val = !!handlereq.default_values[i];
ret = gpiod_direction_output(desc, val);
if (ret)
goto out_free_descs;
} else if (lflags & GPIOHANDLE_REQUEST_INPUT) {
ret = gpiod_direction_input(desc);
if (ret)
goto out_free_descs;
}
dev_dbg(&gdev->dev, "registered chardev handle for line %d\n",
offset);
}
lh->numdescs = handlereq.lines;
fd = anon_inode_getfd("gpio-linehandle",
&linehandle_fileops,
lh,
O_RDONLY | O_CLOEXEC);
if (fd < 0) {
ret = fd;
goto out_free_descs;
}
handlereq.fd = fd;
if (copy_to_user(ip, &handlereq, sizeof(handlereq)))
return -EFAULT;
dev_dbg(&gdev->dev, "registered chardev handle for %d lines\n",
lh->numdescs);
return 0;
out_free_descs:
for (; i >= 0; i--)
gpiod_free(lh->descs[i]);
kfree(lh->label);
out_free_lh:
kfree(lh);
put_device(&gdev->dev);
return ret;
}
/** /**
* gpio_ioctl() - ioctl handler for the GPIO chardev * gpio_ioctl() - ioctl handler for the GPIO chardev
*/ */
...@@ -385,6 +576,8 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) ...@@ -385,6 +576,8 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
if (copy_to_user(ip, &lineinfo, sizeof(lineinfo))) if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
return -EFAULT; return -EFAULT;
return 0; return 0;
} else if (cmd == GPIO_GET_LINEHANDLE_IOCTL) {
return linehandle_create(gdev, ip);
} }
return -EINVAL; return -EINVAL;
} }
......
/* /*
* <linux/gpio.h> - userspace ABI for the GPIO character devices * <linux/gpio.h> - userspace ABI for the GPIO character devices
* *
* Copyright (C) 2015 Linus Walleij * Copyright (C) 2016 Linus Walleij
* *
* This program is free software; you can redistribute it and/or modify it * This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by * under the terms of the GNU General Public License version 2 as published by
...@@ -26,8 +26,8 @@ struct gpiochip_info { ...@@ -26,8 +26,8 @@ struct gpiochip_info {
__u32 lines; __u32 lines;
}; };
/* Line is in use by the kernel */ /* Informational flags */
#define GPIOLINE_FLAG_KERNEL (1UL << 0) #define GPIOLINE_FLAG_KERNEL (1UL << 0) /* Line used by the kernel */
#define GPIOLINE_FLAG_IS_OUT (1UL << 1) #define GPIOLINE_FLAG_IS_OUT (1UL << 1)
#define GPIOLINE_FLAG_ACTIVE_LOW (1UL << 2) #define GPIOLINE_FLAG_ACTIVE_LOW (1UL << 2)
#define GPIOLINE_FLAG_OPEN_DRAIN (1UL << 3) #define GPIOLINE_FLAG_OPEN_DRAIN (1UL << 3)
...@@ -52,7 +52,62 @@ struct gpioline_info { ...@@ -52,7 +52,62 @@ struct gpioline_info {
char consumer[32]; char consumer[32];
}; };
/* Maximum number of requested handles */
#define GPIOHANDLES_MAX 64
/* Request flags */
#define GPIOHANDLE_REQUEST_INPUT (1UL << 0)
#define GPIOHANDLE_REQUEST_OUTPUT (1UL << 1)
#define GPIOHANDLE_REQUEST_ACTIVE_LOW (1UL << 2)
#define GPIOHANDLE_REQUEST_OPEN_DRAIN (1UL << 3)
#define GPIOHANDLE_REQUEST_OPEN_SOURCE (1UL << 4)
/**
* struct gpiohandle_request - Information about a GPIO handle request
* @lineoffsets: an array 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, OR:ed
* 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 (low) or
* 1 (high), anything else than 0 or 1 will be interpreted as 1 (high)
* @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: if successful this field will contain a valid anonymous file handle
* after a GPIO_GET_LINEHANDLE_IOCTL operation, zero or negative value
* means error
*/
struct gpiohandle_request {
__u32 lineoffsets[GPIOHANDLES_MAX];
__u32 flags;
__u8 default_values[GPIOHANDLES_MAX];
char consumer_label[32];
__u32 lines;
int fd;
};
#define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info) #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_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
* state of a line, when setting the state of lines these should contain
* the desired target state
*/
struct gpiohandle_data {
__u8 values[GPIOHANDLES_MAX];
};
#define GPIOHANDLE_GET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x08, struct gpiohandle_data)
#define GPIOHANDLE_SET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x09, struct gpiohandle_data)
#endif /* _UAPI_GPIO_H_ */ #endif /* _UAPI_GPIO_H_ */
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