input: matrix-keymap: Add function to read the new DT binding

We now have a binding which adds two parameters to the matrix keypad DT
node. This is separate from the GPIO-driven matrix keypad binding, and
unfortunately incompatible, since that uses row-gpios/col-gpios for the
row and column counts.

So the easiest option here is to provide a function for non-GPIO drivers
to use to decode the binding.

Note: We could in fact create an entirely separate structure to hold
these two fields, but it does not seem worth it, yet. If we have more
parameters then we can add this, and then refactor each driver to hold
such a structure.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Tested-by: Sourav Poddar <sourav.poddar@ti.com> (v2)
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

include/linux/input/matrix_keypad.h

@@ -81,4 +81,23 @@ int matrix_keypad_build_keymap(const struct matrix_keymap_data *keymap_data,
 			       unsigned short *keymap,
 			       struct input_dev *input_dev);
 
+#ifdef CONFIG_OF
+/**
+ * matrix_keypad_parse_of_params() - Read parameters from matrix-keypad node
+ *
+ * @dev: Device containing of_node
+ * @rows: Returns number of matrix rows
+ * @cols: Returns number of matrix columns
+ * @return 0 if OK, <0 on error
+ */
+int matrix_keypad_parse_of_params(struct device *dev,
+				  unsigned int *rows, unsigned int *cols);
+#else
+static inline int matrix_keypad_parse_of_params(struct device *dev,
+				  unsigned int *rows, unsigned int *cols)
+{
+	return -ENOSYS;
+}
+#endif /* CONFIG_OF */
+
 #endif /* _MATRIX_KEYPAD_H */