dm: add dev_read_u32()

dev_read_u32_default() always returns something even when the property
is missing.  So, it is impossible to do nothing in the case.  One
solution is to use ofnode_read_u32() instead, but adding dev_read_u32()
will be helpful.

BTW, Linux has an equvalent function, device_property_read_u32();
it is clearer that it reads a property.  I cannot understand the
behavior of dev_read_u32() from its name.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

drivers/core/read.c

@@ -10,6 +10,11 @@
 #include <mapmem.h>
 #include <dm/of_access.h>
 
+int dev_read_u32(struct udevice *dev, const char *propname, u32 *outp)
+{
+	return ofnode_read_u32(dev_ofnode(dev), propname, outp);
+}
+
 int dev_read_u32_default(struct udevice *dev, const char *propname, int def)
 {
 	return ofnode_read_u32_default(dev_ofnode(dev), propname, def);

include/dm/read.h

@@ -45,6 +45,16 @@ static inline bool dev_of_valid(struct udevice *dev)
 }
 
 #ifndef CONFIG_DM_DEV_READ_INLINE
+/**
+ * dev_read_u32() - read a 32-bit integer from a device's DT property
+ *
+ * @dev:	device to read DT property from
+ * @propname:	name of the property to read from
+ * @outp:	place to put value (if found)
+ * @return 0 if OK, -ve on error
+ */
+int dev_read_u32(struct udevice *dev, const char *propname, u32 *outp);
+
 /**
  * dev_read_u32_default() - read a 32-bit integer from a device's DT property
  *
@@ -412,6 +422,12 @@ int dev_read_resource_byname(struct udevice *dev, const char *name,
 
 #else /* CONFIG_DM_DEV_READ_INLINE is enabled */
 
+static inline int dev_read_u32(struct udevice *dev,
+			       const char *propname, u32 *outp)
+{
+	return ofnode_read_u32(dev_ofnode(dev), propname, outp);
+}
+
 static inline int dev_read_u32_default(struct udevice *dev,
 				       const char *propname, int def)
 {