linux-kernel - Re: [PATCH] Open Firmware device tree virtual filesystem

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Message-Id: <f8739cc0d5fe2c757eae0af65b6049d9@kernel.crashing.org>
Date:	Tue, 2 Jan 2007 13:28:52 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	linux-kernel@...r.kernel.org, devel@...top.org,
	David Miller <davem@...emloft.net>, David Kahn <dmk@...x.com>,
	wmb@...mworks.com, hch@...radead.org, jg@...top.org
Subject: Re: [PATCH] Open Firmware device tree virtual filesystem

>> IMHO, the directory entries in the filesystem
>> should be in the form "node-name@...t-address" (eg: /pci@1f,0,
>> "pci" is the node name, "@" is the separator character defined
>> by IEEE 1275, and "1f,0" is the unit-address,
>> which are always guaranteed to be unique.
>
> They should be. The problem is buggy OF implementations. For example,
> both IBM and Apple OFs have the nasty habit of having under the CPU
> nodes an "l2-cache" node with no unit-address -and- a property with the
> same name

That is perfectly valid FWIW.  Not a "best practice" or anything,
but valid nonetheless.

Device tree semantics do not fit POSIX filesystem semantics 100%,
you do need some workarounds for some edge cases yes.

>> It's
>> not possible to have two ambiguously fully qualified nodes in the OFW
>> device tree, otherwise you would never be able to select
>> a specific one by name.
>
> Well, it happens to be the case though. The code is to work around 
> that.
> A normal bug-free tree should never trigger the workarounds.

Well it's not *technically* a bug to have two device nodes with
an exact identical path in OF, but sure :-)


Segher

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