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: Michael Welling <mwelling@ieee.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 24f60d2..5f2e73e 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -21,6 +21,7 @@
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/compat.h>
+#include <linux/anon_inodes.h>
#include <uapi/linux/gpio.h>
#include "gpiolib.h"
@@ -310,6 +311,196 @@
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
*/
@@ -385,6 +576,8 @@
if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
return -EFAULT;
return 0;
+ } else if (cmd == GPIO_GET_LINEHANDLE_IOCTL) {
+ return linehandle_create(gdev, ip);
}
return -EINVAL;
}