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

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Date:	Tue, 2 Jan 2007 22:40:17 +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>,
	Mitch Bradley <wmb@...mworks.com>, jg@...top.org
Subject: Re: [PATCH] Open Firmware device tree virtual filesystem

>> The kernel doesn't care if one CPU is in OF land while the others
>> are doing other stuff -- well you have to make sure the OF won't
>> try to use a hardware device at the same time as the kernel, true.
>
> That statement alone hides an absolute can of worms btw ;-)

Oh I know.  With a sane OF implementation, things will work
out fine though.

>> I'm a bit concerned about the 100kB or so of data duplication
>> (on a *quite big* device tree), and the extra code you need
>> (all changes have to be done to both tree copies).  Maybe
>> I shouldn't be worried; still, it's obviously not a great
>> idea to *require* any arch to get and keep a full copy of
>> the tree -- it's wasteful and unnecessary.
>
> Well, big device-trees generally are on big machines with enough memory
> not to care and the only platform I know where the DT can actually
> change over time is IBM pSeries when doing DLPAR, in which case, OF is
> dead, it all happens via magic HV/RTAS calls and the kernel is
> -supposed- to maintain it's own copy and add/remove nodes from it.

You're almost convincing me.  I'll sleep on it a night.


Segher

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