For devices connecting to ITS, it needs dev id to identify
itself, and this dev id is represented in the IORT table in
named componant node [1] for platform devices, so in this
patch we will scan the IORT to retrieve device's dev id.

Introduce iort_pmsi_get_dev_id() with pointer dev passed
in for that purpose.

[1]: https://static.docs.arm.com/den0049/b/DEN0049B_IO_Remapping_Table.pdf

Signed-off-by: Hanjun Guo <redacted>
Tested-by: Sinan Kaya <redacted>
Tested-by: Majun <redacted>
Tested-by: Xinwei Kong <kong.kongxinwei@hisilicon.com>
Cc: Marc Zyngier <redacted>
Cc: Lorenzo Pieralisi <redacted>
Cc: Tomasz Nowicki <redacted>
Cc: Thomas Gleixner <redacted>
---
 drivers/acpi/arm64/iort.c                     | 26 ++++++++++++++++++++++++++
 drivers/irqchip/irq-gic-v3-its-platform-msi.c |  4 +++-
 include/linux/acpi_iort.h                     |  8 ++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
index 174e983..ab7bae7 100644
--- a/drivers/acpi/arm64/iort.c
+++ b/drivers/acpi/arm64/iort.c

@@ -444,6 +444,32 @@ u32 iort_msi_map_rid(struct device *dev, u32 req_id)
 }

 /**
+ * iort_pmsi_get_dev_id() - Get the device id for a device
+ * @dev: The device for which the mapping is to be done.
+ * @dev_id: The device ID found.
+ *
+ * Returns: 0 for successful find a dev id, errors otherwise
+ */
+int iort_pmsi_get_dev_id(struct device *dev, u32 *dev_id)
+{
+	struct acpi_iort_node *node;
+
+	if (!iort_table)
+		return -ENODEV;
+
+	node = iort_find_dev_node(dev);
+	if (!node) {
+		dev_err(dev, "can't find related IORT node\n");
+		return -ENODEV;
+	}
+
+	if(!iort_node_get_id(node, dev_id, IORT_MSI_TYPE, 0))
+		return -ENODEV;
+
+	return 0;
+}
+
+/**