device property: Allow const parameter to dev_fwnode()

It's not fully correct to take a const parameter pointer to a struct
and return a non-const pointer to a member of that struct.

Instead, introduce a const version of the dev_fwnode() API which takes
and returns const pointers and use it where it's applicable.

With this, convert dev_fwnode() to be a macro wrapper on top of const
and non-const APIs that chooses one based on the type.

Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Fixes: aade55c ("device property: Add const qualifier to device_get_match_data() parameter")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://lore.kernel.org/r/20221004092129.19412-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/property.c

@@ -17,12 +17,19 @@
 #include <linux/property.h>
 #include <linux/phy.h>
 
-struct fwnode_handle *dev_fwnode(const struct device *dev)
+struct fwnode_handle *__dev_fwnode(struct device *dev)
 {
 	return IS_ENABLED(CONFIG_OF) && dev->of_node ?
 		of_fwnode_handle(dev->of_node) : dev->fwnode;
 }
-EXPORT_SYMBOL_GPL(dev_fwnode);
+EXPORT_SYMBOL_GPL(__dev_fwnode);
+
+const struct fwnode_handle *__dev_fwnode_const(const struct device *dev)
+{
+	return IS_ENABLED(CONFIG_OF) && dev->of_node ?
+		of_fwnode_handle(dev->of_node) : dev->fwnode;
+}
+EXPORT_SYMBOL_GPL(__dev_fwnode_const);
 
 /**
  * device_property_present - check if a property of a device is present

include/linux/property.h

@@ -32,7 +32,12 @@ enum dev_dma_attr {
 	DEV_DMA_COHERENT,
 };
 
-struct fwnode_handle *dev_fwnode(const struct device *dev);
+const struct fwnode_handle *__dev_fwnode_const(const struct device *dev);
+struct fwnode_handle *__dev_fwnode(struct device *dev);
+#define dev_fwnode(dev)							\
+	_Generic((dev),							\
+		 const struct device *: __dev_fwnode_const,	\
+		 struct device *: __dev_fwnode)(dev)
 
 bool device_property_present(struct device *dev, const char *propname);
 int device_property_read_u8_array(struct device *dev, const char *propname,