[RFC PATCH 6/6] Input: Add EVIOCGBTNCNT

["Tomasz Pakuła" <tomasz.pakula.oficjalny@gmail.com>]

Allow userspace to get the button count of input
devices. currently only used for Joysticks which
includes Simracing and Simflight hardware. Such
devices are always defined as generic joysticks.

Signed-off-by: Tomasz Pakuła <tomasz.pakula.oficjalny@gmail.com>
---
 drivers/input/evdev.c      | 5 +++++
 include/uapi/linux/input.h | 1 +
 2 files changed, 6 insertions(+)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 90ff6be85cf4..b90dc035c0b3 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -1134,6 +1134,11 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd,
 
 	case EVIOCSKEYCODE_V2:
 		return evdev_handle_set_keycode_v2(dev, p);
+
+	case EVIOCGBTNCNT:
+		if (copy_to_user(p, &dev->button_count, sizeof(unsigned int)))
+			return -EFAULT;
+		return 0;
 	}
 
 	size = _IOC_SIZE(cmd);
diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
index 6aa703fcfcfb..3d1b17ebcdfc 100644
--- a/include/uapi/linux/input.h
+++ b/include/uapi/linux/input.h
@@ -174,6 +174,7 @@ struct input_mask {
 #define EVIOCGLED(len)		_IOC(_IOC_READ, 'E', 0x19, len)		/* get all LEDs */
 #define EVIOCGSND(len)		_IOC(_IOC_READ, 'E', 0x1a, len)		/* get all sounds status */
 #define EVIOCGSW(len)		_IOC(_IOC_READ, 'E', 0x1b, len)		/* get all switch states */
+#define EVIOCGBTNCNT		_IOR('E', 0x1c, unsigned int)		/* get button count */
 
 #define EVIOCGBIT(ev,len)	_IOC(_IOC_READ, 'E', 0x20 + (ev), len)	/* get event bits */
 #define EVIOCGABS(abs)		_IOR('E', 0x40 + (abs), struct input_absinfo)	/* get abs value/limits */
-- 
2.52.0