Reusing DTSI files across trees with differing numbers of address-cells

From: Stepan Moskovchenko
Date: Fri Apr 26 2013 - 19:18:17 EST

Hello. I am creating a DTS file for an ARM (Qualcomm MSM) target which supports LPAE, meaning that the target is capable of addressing memory beyond the standard 4GB boundary. To account for the fact that the memory node can contain reg addresses that exceed 32 bits, I am setting #address-cells and #size-cells to 2 at the top level of my tree, since this is what the kernel will use when parsing the memory node.

However, my internal tree contains multiple DTSI files with definitions for some hardware blocks that are used across multiple MSM targets, including ones that have #address-cells and #size-cells set to 1 at the top level, I would like to re-use some of these files in the tree for my LPAE-based target. Additionally, most MSM I/O devices are declared at the top level of the tree, rather than on a dedicated simple-bus.

To allow reuse of common hardware block definitions, I am considering moving all the MSM memory-mapped I/O devices to a dedicated /soc node (per the Power spec), declaring this node as a simple-bus with #address-cells and #size-cells of 1, and using the ranges property to map this bus into the top-level address space. Since MSM I/O devices are located at addresses below 4GB, I believe it is okay to keep them on a simple-bus with #address-cells=1.

Does this seem like a reasonable approach?


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