Add a helper function wrapping internal reserved memory
device_init call and expose it externally.

Use the new helper function within of_reserved_mem_device_init_by_idx().

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 drivers/of/of_reserved_mem.c    | 68 ++++++++++++++++++++++++++---------------
 include/linux/of_reserved_mem.h |  8 +++++
 2 files changed, 52 insertions(+), 24 deletions(-)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 1fd28f8056108..26ca871f7f919 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -605,6 +605,49 @@ struct rmem_assigned_device {
 static LIST_HEAD(of_rmem_assigned_device_list);
 static DEFINE_MUTEX(of_rmem_assigned_device_mutex);
 
+/**
+ * of_reserved_mem_device_init_with_mem() - assign reserved memory region to
+ *					    given device
+ * @dev:	Pointer to the device to configure
+ * @rmem:	Reserved memory region to assign
+ *
+ * This function assigns respective DMA-mapping operations based on the
+ * reserved memory region already provided in @rmem to the @dev device,
+ * without walking DT nodes.
+ *
+ * Returns error code or zero on success.
+ */
+int of_reserved_mem_device_init_with_mem(struct device *dev,
+					 struct reserved_mem *rmem)
+{
+	struct rmem_assigned_device *rd;
+	int ret;
+
+	if (!dev || !rmem || !rmem->ops || !rmem->ops->device_init)
+		return -EINVAL;
+
+	rd = kmalloc_obj(struct rmem_assigned_device);
+	if (!rd)
+		return -ENOMEM;
+
+	ret = rmem->ops->device_init(rmem, dev);
+	if (ret == 0) {
+		rd->dev = dev;
+		rd->rmem = rmem;
+
+		mutex_lock(&of_rmem_assigned_device_mutex);
+		list_add(&rd->list, &of_rmem_assigned_device_list);
+		mutex_unlock(&of_rmem_assigned_device_mutex);
+
+		dev_info(dev, "assigned reserved memory node %s\n", rmem->name);
+	} else {
+		kfree(rd);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(of_reserved_mem_device_init_with_mem);
+
 /**
  * of_reserved_mem_device_init_by_idx() - assign reserved memory region to
  *					  given device
@@ -623,10 +666,8 @@ static DEFINE_MUTEX(of_rmem_assigned_device_mutex);
 int of_reserved_mem_device_init_by_idx(struct device *dev,
 				       struct device_node *np, int idx)
 {
-	struct rmem_assigned_device *rd;
 	struct device_node *target;
 	struct reserved_mem *rmem;
-	int ret;
 
 	if (!np || !dev)
 		return -EINVAL;
@@ -643,28 +684,7 @@ int of_reserved_mem_device_init_by_idx(struct device *dev,
 	rmem = of_reserved_mem_lookup(target);
 	of_node_put(target);
 
-	if (!rmem || !rmem->ops || !rmem->ops->device_init)
-		return -EINVAL;
-
-	rd = kmalloc_obj(struct rmem_assigned_device);
-	if (!rd)
-		return -ENOMEM;
-
-	ret = rmem->ops->device_init(rmem, dev);
-	if (ret == 0) {
-		rd->dev = dev;
-		rd->rmem = rmem;
-
-		mutex_lock(&of_rmem_assigned_device_mutex);
-		list_add(&rd->list, &of_rmem_assigned_device_list);
-		mutex_unlock(&of_rmem_assigned_device_mutex);
-
-		dev_info(dev, "assigned reserved memory node %s\n", rmem->name);
-	} else {
-		kfree(rd);
-	}
-
-	return ret;
+	return of_reserved_mem_device_init_with_mem(dev, rmem);
 }
 EXPORT_SYMBOL_GPL(of_reserved_mem_device_init_by_idx);
 
diff --git a/include/linux/of_reserved_mem.h b/include/linux/of_reserved_mem.h
index f573423359f48..12f7ddb7ee61f 100644
--- a/include/linux/of_reserved_mem.h
+++ b/include/linux/of_reserved_mem.h
@@ -32,6 +32,8 @@ typedef int (*reservedmem_of_init_fn)(struct reserved_mem *rmem);
 #define RESERVEDMEM_OF_DECLARE(name, compat, init)			\
 	_OF_DECLARE(reservedmem, name, compat, init, reservedmem_of_init_fn)
 
+int of_reserved_mem_device_init_with_mem(struct device *dev,
+					 struct reserved_mem *rmem);
 int of_reserved_mem_device_init_by_idx(struct device *dev,
 				       struct device_node *np, int idx);
 int of_reserved_mem_device_init_by_name(struct device *dev,
@@ -51,6 +53,12 @@ int of_reserved_mem_region_count(const struct device_node *np);
 #define RESERVEDMEM_OF_DECLARE(name, compat, init)			\
 	_OF_DECLARE_STUB(reservedmem, name, compat, init, reservedmem_of_init_fn)
 
+static inline int of_reserved_mem_device_init_with_mem(struct device *dev,
+						       struct reserved_mem *rmem)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int of_reserved_mem_device_init_by_idx(struct device *dev,
 					struct device_node *np, int idx)
 {

-- 
2.52.0

On Fri, Mar 06, 2026 at 11:36:34AM +0100, Albert Esteve wrote:
> Add a helper function wrapping internal reserved memory
> device_init call and expose it externally.

Why?

The diff tells us what. The commit msg needs to tell us why. Maybe the 
rest of the series explains it, but this commit needs to stand on its 
own.

> 
> Use the new helper function within of_reserved_mem_device_init_by_idx().
> 
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---

Version history?

>  drivers/of/of_reserved_mem.c    | 68 ++++++++++++++++++++++++++---------------
>  include/linux/of_reserved_mem.h |  8 +++++
>  2 files changed, 52 insertions(+), 24 deletions(-)

On Sat, Mar 14, 2026 at 12:06 AM Rob Herring <robh@kernel.org> wrote:
>
> On Fri, Mar 06, 2026 at 11:36:34AM +0100, Albert Esteve wrote:
> > Add a helper function wrapping internal reserved memory
> > device_init call and expose it externally.
>
> Why?
>
> The diff tells us what. The commit msg needs to tell us why. Maybe the
> rest of the series explains it, but this commit needs to stand on its
> own.

ACK.

This patch prepares for the heap implementation in patch #4, which
uses the new helper function. I will add the information to the commit
body.

>
> >
> > Use the new helper function within of_reserved_mem_device_init_by_idx().
> >
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
>
> Version history?

You mean track it in the commit body? History is already detailed in
the cover letter.

>
> >  drivers/of/of_reserved_mem.c    | 68 ++++++++++++++++++++++++++---------------
> >  include/linux/of_reserved_mem.h |  8 +++++
> >  2 files changed, 52 insertions(+), 24 deletions(-)
>