linux-kernel - [PATCH 5/6] of: Use the standards compliant default address cells value for x86

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Message-ID: <20241104172001.165640-6-herve.codina@bootlin.com>
Date: Mon,  4 Nov 2024 18:19:59 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lizhi Hou <lizhi.hou@....com>
Cc: linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Allan Nielsen <allan.nielsen@...rochip.com>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	Steen Hegelund <steen.hegelund@...rochip.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Herve Codina <herve.codina@...tlin.com>
Subject: [PATCH 5/6] of: Use the standards compliant default address cells value for x86

The default address cells value is 1.

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

The device tree compiler already use 2 as default value and the powerpc
PROM code also use 2 as default value. Modern implementation should have
the #address-cells property set and should not rely on this default
value.

On x86, an empty root device-tree node is created but as the hardware
is not described by a device-tree passed by the bootloader, this root
device-tree remains empty and so the #address-cells default value is
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),
this default value 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. Restrict the modification to the x86 architecture.

Instead of having 1 for this default value, be consistent with standards
and set the default address cells value to 2 in case of x86.

Signed-off-by: Herve Codina <herve.codina@...tlin.com>
---
 drivers/of/of_private.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 04aa2a91f851..d8353f04af0a 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -29,7 +29,7 @@ struct alias_prop {
 	char stem[];
 };

-#if defined(CONFIG_SPARC)
+#if defined(CONFIG_SPARC) || defined(CONFIG_X86)
 #define OF_ROOT_NODE_ADDR_CELLS_DEFAULT 2
 #else
 #define OF_ROOT_NODE_ADDR_CELLS_DEFAULT 1
-- 
2.46.2