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60bc447c85
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 does not have the #address-cells and the #size-cells properties This leads to the use of the default address cells and size cells values which are defined in the code to 1 for the address cells value and 1 for the size cells value. 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. The device tree compiler already uses 2 as default value for address cells and 1 for size cells. The powerpc PROM code also uses 2 as default value for address cells and 1 for size cells. 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 upper part of a 64-bit value 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 both required #address-cells and #size-cells properties in the device-tree empty node. Use 2 for both properties value in order to fully support 64-bit addresses and sizes on systems using this empty root node. Signed-off-by: Herve Codina <herve.codina@bootlin.com> Link: https://lore.kernel.org/r/20241202131522.142268-6-herve.codina@bootlin.com Signed-off-by: Rob Herring (Arm) <robh@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.