doc: document libinput_device_tablet_pad_get_* error case

Like in libinput_device_switch_has_switch()'s documentation, document
the error case in libinput_device_tablet_pad_get_num_buttons(),
libinput_device_tablet_pad_get_num_rings() and
libinput_device_tablet_pad_get_num_strips().

Signed-off-by: José Expósito <jose.exposito89@gmail.com>

diff --git a/src/libinput.h b/src/libinput.h
index 7c0a9a757e09d8232acbf9d4df6d73f132930e5d..272704956a054e7572e8d414dca117ad5e2b025b 100644 (file)
--- a/src/libinput.h
+++ b/src/libinput.h
@@ -4370,7 +4370,7 @@ libinput_device_switch_has_switch(struct libinput_device *device,
  *
  * @param device A current input device
  *
- * @return The number of buttons supported by the device.
+ * @return The number of buttons supported by the device. -1 on error.
  *
  * @since 1.3
  */
@@ -4385,7 +4385,7 @@ libinput_device_tablet_pad_get_num_buttons(struct libinput_device *device);
  *
  * @param device A current input device
  *
- * @return The number of rings or 0 if the device has no rings.
+ * @return The number of rings or 0 if the device has no rings. -1 on error.
  *
  * @see libinput_event_tablet_pad_get_ring_number
  *
@@ -4402,7 +4402,7 @@ libinput_device_tablet_pad_get_num_rings(struct libinput_device *device);
  *
  * @param device A current input device
  *
- * @return The number of strips or 0 if the device has no strips.
+ * @return The number of strips or 0 if the device has no strips. -1 on error.
  *
  * @see libinput_event_tablet_pad_get_strip_number
  *