gpio: add userspace ABI for GPIO line information

This adds a GPIO line ABI for getting name, label and a few select
flags from the kernel.

This hides the kernel internals and only tells userspace what it
may need to know: the different in-kernel consumers are masked
behind the flag "kernel" and that is all userspace needs to know.

However electric characteristics like active low, open drain etc
are reflected to userspace, as this is important information.

We provide information on all lines on all chips, later on we will
likely add a flag for the chardev consumer so we can filter and
display only the lines userspace actually uses in e.g. lsgpio,
but then we first need an ABI for userspace to grab and use
(get/set/select direction) a GPIO line.

Sample output from "lsgpio" on ux500:

GPIO chip: gpiochip7, "8011e000.gpio", 32 GPIO lines
        line 0: unnamed unlabeled
        line 1: unnamed unlabeled
(...)
        line 25: unnamed "SFH7741 Proximity Sensor" [kernel output open-drain]
        line 26: unnamed unlabeled
(...)

Tested-by: Michael Welling <mwelling@ieee.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 49 insertions, 2 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 797c790aa750..3580c0de9d5a 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -331,14 +331,15 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	struct gpio_device *gdev = filp->private_data;
 	struct gpio_chip *chip = gdev->chip;
 	int __user *ip = (int __user *)arg;
-	struct gpiochip_info chipinfo;
 
 	/* We fail any subsequent ioctl():s when the chip is gone */
 	if (!chip)
 		return -ENODEV;
 
+	/* Fill in the struct and pass to userspace */
 	if (cmd == GPIO_GET_CHIPINFO_IOCTL) {
-		/* Fill in the struct and pass to userspace */
+		struct gpiochip_info chipinfo;
+
 		strncpy(chipinfo.name, dev_name(&gdev->dev),
 			sizeof(chipinfo.name));
 		chipinfo.name[sizeof(chipinfo.name)-1] = '\0';
@@ -349,6 +350,52 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		if (copy_to_user(ip, &chipinfo, sizeof(chipinfo)))
 			return -EFAULT;
 		return 0;
+	} else if (cmd == GPIO_GET_LINEINFO_IOCTL) {
+		struct gpioline_info lineinfo;
+		struct gpio_desc *desc;
+
+		if (copy_from_user(&lineinfo, ip, sizeof(lineinfo)))
+			return -EFAULT;
+		if (lineinfo.line_offset > gdev->ngpio)
+			return -EINVAL;
+
+		desc = &gdev->descs[lineinfo.line_offset];
+		if (desc->name) {
+			strncpy(lineinfo.name, desc->name,
+				sizeof(lineinfo.name));
+			lineinfo.name[sizeof(lineinfo.name)-1] = '\0';
+		} else {
+			lineinfo.name[0] = '\0';
+		}
+		if (desc->label) {
+			strncpy(lineinfo.label, desc->label,
+				sizeof(lineinfo.label));
+			lineinfo.label[sizeof(lineinfo.label)-1] = '\0';
+		} else {
+			lineinfo.label[0] = '\0';
+		}
+
+		/*
+		 * Userspace only need to know that the kernel is using
+		 * this GPIO so it can't use it.
+		 */
+		lineinfo.flags = 0;
+		if (desc->flags & (FLAG_REQUESTED | FLAG_IS_HOGGED |
+				   FLAG_USED_AS_IRQ | FLAG_EXPORT |
+				   FLAG_SYSFS))
+			lineinfo.flags |= GPIOLINE_FLAG_KERNEL;
+		if (desc->flags & FLAG_IS_OUT)
+			lineinfo.flags |= GPIOLINE_FLAG_IS_OUT;
+		if (desc->flags & FLAG_ACTIVE_LOW)
+			lineinfo.flags |= GPIOLINE_FLAG_ACTIVE_LOW;
+		if (desc->flags & FLAG_OPEN_DRAIN)
+			lineinfo.flags |= GPIOLINE_FLAG_OPEN_DRAIN;
+		if (desc->flags & FLAG_OPEN_SOURCE)
+			lineinfo.flags |= GPIOLINE_FLAG_OPEN_SOURCE;
+
+		if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
+			return -EFAULT;
+		return 0;
 	}
 	return -EINVAL;
 }