Re: [PATCH] Open Firmware device tree virtual filesystem

From: Mitch Bradley <wmb@xxxxxxxxxxxxx>
Date: Sat, 30 Dec 2006 15:38:46 -1000

Request for comments.

This patch creates a virtual filesystem that represents an Open Firmware
device tree. It has been tested on an OLPC x86 system, but the code is
not processor-specific (apart from its current location under arch/i386).

It requires an Open Firmware implementation that can stay resident during
Linux startup.

It is similar in some respect to fs/proc/proc_devtree.c , but does not
use procfs, nor does it require an intermediate layer of code to
create a flattened representation of the device tree.

The patch applies cleanly against the current version of
git://dev.laptop.org/olpc-2.6 . (commit 5b9429be6056864b938ff6f39e5df3cecbbfcf4b).

Please cc me (Mitch Bradley <wmb@xxxxxxxxxxxxx>) on comments.

Can we please not have N different interfaces to the open-firmware
calls so that perhaps powerpc and Sparc have a chance of using this
code too?

On sparc and powerpc, we even build an in-kernel data structure of the
entire open-firmware device tree that code like your's could use if
you make a simple setup layer for i386 as well. We have interfaces for
modifying property values at run time too.

I would strongly suggest looking at things like
arch/{sparc,sparc64,powerpc}/kernel/prom.c and
include/asm-{sparc,sparc64,powerpc}/prom.h and
arch/{sparc,sparc64,powerpc}/kernel/of_device.c and
include/asm-{sparc,sparc64,powerpc}/of_device.h
since we've already invested a lot of thought and
infrastructure into providing interfaces to this information
on powerpc and the two sparc platforms.

Thanks.
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