dts: edtlib: Turn global spi_dev_cs_gpio() into Node.spi_cs_gpio

spi_dev_cs_gpio() takes a Node and returns the chip select GPIO for it.
Having that information available directly from Node is neater, so turn
it into a Node.spi_cs_gpio property instead.

That gets rid of the only public global function in edtlib, which might
make the API design clearer too.

Tested with the sensortile_box board, which uses SPI chip select.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>

scripts/dts/edtlib.py

@@ -789,6 +789,11 @@ class Node:
     flash_controller:
       The flash controller for the node. Only meaningful for nodes representing
       flash partitions.
+
+    spi_cs_gpio:
+      The device's SPI GPIO chip select as a ControllerAndData instance, if it
+      exists, and None otherwise. See
+      Documentation/devicetree/bindings/spi/spi-controller.yaml in the Linux kernel.
     """
     @property
     def name(self):
@@ -927,6 +932,28 @@ class Node:
             return controller.parent
         return controller
 
+    @property
+    def spi_cs_gpio(self):
+        "See the class docstring"
+
+        if not (self.on_bus == "spi" and "cs-gpios" in self.bus_node.props):
+            return None
+
+        if not self.regs:
+            _err("{!r} needs a 'reg' property, to look up the chip select index "
+                 "for SPI".format(self))
+
+        parent_cs_lst = self.bus_node.props["cs-gpios"].val
+
+        # cs-gpios is indexed by the unit address
+        cs_index = self.regs[0].addr
+        if cs_index >= len(parent_cs_lst):
+            _err("index from 'regs' in {!r} ({}) is >= number of cs-gpios "
+                 "in {!r} ({})".format(
+                     self, cs_index, self.bus_node, len(parent_cs_lst)))
+
+        return parent_cs_lst[cs_index]
+
     def __repr__(self):
         return "<Node {} in '{}', {}>".format(
             self.path, self.edt.dts_path,
@@ -1504,35 +1531,6 @@ class EDTError(Exception):
     "Exception raised for devicetree- and binding-related errors"
 
 
-#
-# Public global functions
-#
-
-
-def spi_dev_cs_gpio(node):
-    # Returns an SPI device's GPIO chip select if it exists, as a
-    # ControllerAndData instance, and None otherwise. See
-    # Documentation/devicetree/bindings/spi/spi-bus.txt in the Linux kernel.
-
-    if not (node.on_bus == "spi" and "cs-gpios" in node.bus_node.props):
-        return None
-
-    if not node.regs:
-        _err("{!r} needs a 'reg' property, to look up the chip select index "
-             "for SPI".format(node))
-
-    parent_cs_lst = node.bus_node.props["cs-gpios"].val
-
-    # cs-gpios is indexed by the unit address
-    cs_index = node.regs[0].addr
-    if cs_index >= len(parent_cs_lst):
-        _err("index from 'regs' in {!r} ({}) is >= number of cs-gpios "
-             "in {!r} ({})".format(
-                 node, cs_index, node.bus_node, len(parent_cs_lst)))
-
-    return parent_cs_lst[cs_index]
-
-
 #
 # Private global functions
 #

scripts/dts/gen_defines.py

@@ -549,7 +549,7 @@ def write_irqs(node):
 def write_spi_dev(node):
     # Writes SPI device GPIO chip select data if there is any
 
-    cs_gpio = edtlib.spi_dev_cs_gpio(node)
+    cs_gpio = node.spi_cs_gpio
     if cs_gpio is not None:
         write_phandle_val_list_entry(node, cs_gpio, None, "CS_GPIOS")