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

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Date:	Fri, 26 Apr 2013 16:17:52 -0700
From:	Stepan Moskovchenko <stepanm@...eaurora.org>
To:	devicetree-discuss@...ts.ozlabs.org
CC:	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Reusing DTSI files across trees with differing numbers of address-cells

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?

Thanks
Steve

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