Add a helper function that retrieves RMR memory descriptors
associated with a given IOMMU. This will be used by IOMMU
drivers to setup necessary mappings.

Now that we have this, invoke it from the generic helper
interface.

Signed-off-by: Shameer Kolothum <redacted>
---
 drivers/acpi/arm64/iort.c | 50 +++++++++++++++++++++++++++++++++++++++
 drivers/iommu/dma-iommu.c |  4 ++++
 include/linux/acpi_iort.h |  7 ++++++
 3 files changed, 61 insertions(+)

diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
index fea1ffaedf3b..01917caf58de 100644
--- a/drivers/acpi/arm64/iort.c
+++ b/drivers/acpi/arm64/iort.c

@@ -12,6 +12,7 @@
 
 #include <linux/acpi_iort.h>
 #include <linux/bitfield.h>
+#include <linux/dma-iommu.h>
 #include <linux/iommu.h>
 #include <linux/kernel.h>
 #include <linux/list.h>

@@ -837,6 +838,53 @@ static inline int iort_add_device_replay(struct device *dev)
 	return err;
 }
 
+/**
+ * iort_iommu_get_rmrs - Helper to retrieve RMR info associated with IOMMU
+ * @iommu: fwnode for the IOMMU
+ * @head: RMR list head to be populated
+ *
+ * Returns: 0 on success, <0 failure
+ */
+int iort_iommu_get_rmrs(struct fwnode_handle *iommu_fwnode,
+			struct list_head *head)
+{
+	struct iort_rmr_entry *e;
+	struct acpi_iort_node *iommu;
+	int rmrs = 0;
+
+	iommu = iort_get_iort_node(iommu_fwnode);
+	if (!iommu || list_empty(&iort_rmr_list))
+		return -ENODEV;
+
+	list_for_each_entry(e, &iort_rmr_list, list) {
+		int prot = IOMMU_READ | IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO;