[PATCH v2 5/6] of: Add #address-cells/#size-cells in the device-tree root empty node

[Herve Codina <herve.codina@bootlin.com>]

On systems where ACPI is enabled or when a device-tree is not passed to
the kernel by the bootloader, a device-tree root empty node is created.
This device-tree root empty node doesn't have the #address-cells and the

This leads to the use of the default address cells and size cells values
which are defined in the code to 1 for address cells and 1 for size cells

According to the devicetree specification and the OpenFirmware standard
(IEEE 1275-1994) the default value for #address-cells should be 2.

Also, according to the devicetree specification, the #address-cells and
the #size-cells are required properties in the root node.

Modern implementation should have the #address-cells and the #size-cells
properties set and should not rely on default values.

On x86, this root empty node is used and the code default values are
used.

In preparation of the support for device-tree overlay on PCI devices
feature on x86 (i.e. the creation of the PCI root bus device-tree node),
the default value for #address-cells needs to be updated. Indeed, on
x86_64, addresses are on 64bits and the upper part of an address is
needed for correct address translations. On x86_32 having the default
value updated does not lead to issues while the uppert part of a 64bits
address is zero.

Changing the default value for all architectures may break device-tree
compatibility. Indeed, existing dts file without the #address-cells
property set in the root node will not be compatible with this
modification.

Instead of updating default values, add required #address-cells and

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/of/empty_root.dts | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/of/empty_root.dts b/drivers/of/empty_root.dts
index cf9e97a60f48..5017579f34dc 100644
--- a/drivers/of/empty_root.dts
+++ b/drivers/of/empty_root.dts
@@ -2,5 +2,11 @@
 /dts-v1/;
 
 / {
-
+	/*
+	 * #address-cells/#size-cells are required properties at root node
+	 * according to the devicetree specification. Use same values as default
+	 * values mentioned for #address-cells/#size-cells properties.
+	 */
+	#address-cells = <0x02>;
+	#size-cells = <0x01>;
 };
-- 
2.46.2