of: reserved_mem: Add functions to parse "memory-region"

JIRA: https://issues.redhat.com/browse/RHEL-125402

commit f4fcfdd
Author: Rob Herring (Arm) <robh@kernel.org>
Date:   2025-04-23 14:42:13 -0500

    of: reserved_mem: Add functions to parse "memory-region"

    Drivers with "memory-region" properties currently have to do their own
    parsing of "memory-region" properties. The result is all the drivers
    have similar patterns of a call to parse "memory-region" and then get
    the region's address and size. As this is a standard property, it should
    have common functions for drivers to use. Add new functions to count the
    number of regions and retrieve the region's address as a resource.

    Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
    Acked-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
    Link: https://lore.kernel.org/r/20250423-dt-memory-region-v2-v2-1-2fbd6ebd3c88@kernel.org
    Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Signed-off-by: Maxime Ripard <mripard@redhat.com>

Author: Maxime Ripard

drivers/of/of_reserved_mem.c

@@ -12,6 +12,7 @@
 #define pr_fmt(fmt)	"OF: reserved mem: " fmt
 
 #include <linux/err.h>
+#include <linux/ioport.h>
 #include <linux/libfdt.h>
 #include <linux/of.h>
 #include <linux/of_fdt.h>
@@ -740,3 +741,82 @@ struct reserved_mem *of_reserved_mem_lookup(struct device_node *np)
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(of_reserved_mem_lookup);
+
+/**
+ * of_reserved_mem_region_to_resource() - Get a reserved memory region as a resource
+ * @np:		node containing 'memory-region' property
+ * @idx:	index of 'memory-region' property to lookup
+ * @res:	Pointer to a struct resource to fill in with reserved region
+ *
+ * This function allows drivers to lookup a node's 'memory-region' property
+ * entries by index and return a struct resource for the entry.
+ *
+ * Returns 0 on success with @res filled in. Returns -ENODEV if 'memory-region'
+ * is missing or unavailable, -EINVAL for any other error.
+ */
+int of_reserved_mem_region_to_resource(const struct device_node *np,
+				       unsigned int idx, struct resource *res)
+{
+	struct reserved_mem *rmem;
+
+	if (!np)
+		return -EINVAL;
+
+	struct device_node __free(device_node) *target = of_parse_phandle(np, "memory-region", idx);
+	if (!target || !of_device_is_available(target))
+		return -ENODEV;
+
+	rmem = of_reserved_mem_lookup(target);
+	if (!rmem)
+		return -EINVAL;
+
+	resource_set_range(res, rmem->base, rmem->size);
+	res->name = rmem->name;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_region_to_resource);
+
+/**
+ * of_reserved_mem_region_to_resource_byname() - Get a reserved memory region as a resource
+ * @np:		node containing 'memory-region' property
+ * @name:	name of 'memory-region' property entry to lookup
+ * @res:	Pointer to a struct resource to fill in with reserved region
+ *
+ * This function allows drivers to lookup a node's 'memory-region' property
+ * entries by name and return a struct resource for the entry.
+ *
+ * Returns 0 on success with @res filled in, or a negative error-code on
+ * failure.
+ */
+int of_reserved_mem_region_to_resource_byname(const struct device_node *np,
+					      const char *name,
+					      struct resource *res)
+{
+	int idx;
+
+	if (!name)
+		return -EINVAL;
+
+	idx = of_property_match_string(np, "memory-region-names", name);
+	if (idx < 0)
+		return idx;
+
+	return of_reserved_mem_region_to_resource(np, idx, res);
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_region_to_resource_byname);
+
+/**
+ * of_reserved_mem_region_count() - Return the number of 'memory-region' entries
+ * @np:		node containing 'memory-region' property
+ *
+ * This function allows drivers to retrieve the number of entries for a node's
+ * 'memory-region' property.
+ *
+ * Returns the number of entries on success, or negative error code on a
+ * malformed property.
+ */
+int of_reserved_mem_region_count(const struct device_node *np)
+{
+	return of_count_phandle_with_args(np, "memory-region", NULL);
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_region_count);

include/linux/of_reserved_mem.h

@@ -7,6 +7,7 @@
 
 struct of_phandle_args;
 struct reserved_mem_ops;
+struct resource;
 
 struct reserved_mem {
 	const char			*name;
@@ -39,6 +40,12 @@ int of_reserved_mem_device_init_by_name(struct device *dev,
 void of_reserved_mem_device_release(struct device *dev);
 
 struct reserved_mem *of_reserved_mem_lookup(struct device_node *np);
+int of_reserved_mem_region_to_resource(const struct device_node *np,
+				       unsigned int idx, struct resource *res);
+int of_reserved_mem_region_to_resource_byname(const struct device_node *np,
+					      const char *name, struct resource *res);
+int of_reserved_mem_region_count(const struct device_node *np);
+
 #else
 
 #define RESERVEDMEM_OF_DECLARE(name, compat, init)			\
@@ -63,6 +70,25 @@ static inline struct reserved_mem *of_reserved_mem_lookup(struct device_node *np
 {
 	return NULL;
 }
+
+static inline int of_reserved_mem_region_to_resource(const struct device_node *np,
+						     unsigned int idx,
+						     struct resource *res)
+{
+	return -ENOSYS;
+}
+
+static inline int of_reserved_mem_region_to_resource_byname(const struct device_node *np,
+							    const char *name,
+							    struct resource *res)
+{
+	return -ENOSYS;
+}
+
+static inline int of_reserved_mem_region_count(const struct device_node *np)
+{
+	return 0;
+}
 #endif
 
 /**