linux-kernel - Re: [PATCH 1/2] OLPC: Add support for calling into Open Firmware

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Date:	Mon, 21 Apr 2008 16:54:13 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	Mitch Bradley <wmb@...mworks.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joseph Fannin <jfannin@...il.com>,
	linux-kernel@...r.kernel.org, jordan.crouse@....com
Subject: Re: [PATCH 1/2] OLPC: Add support for calling into Open Firmware

On Mon, 2008-04-21 at 10:24 -0400, Andres Salomon wrote:
> I'm not actually convinced that we *do* want to keep OFW resident in memory,
> especially given the memory tricks we need to play.  I also don't actually
> like the OFW interface that we.  The debugging aspect of it was a
> compelling argument up until a week ago (when kernel debuggers started
> finally finding their way into the kernel).

I don't actually think that the debugging aspect was _ever_ a compelling
argument. It might have made it theoretically possible for _Mitch_ to
debug kernel problems, should he be inclined to do so -- but for the
rest of us mere mortals it's just a PITA trying to keep OpenFirmware
live. A gdb stub is much more useful, in my experience.

> However, until we clean up the promfs stuff, there's no chance of getting
> an OFW device tree upstream.

I see no reason why we shouldn't be able to create a 'flattened'
device-tree during early boot, like the PowerPC kernel does. And use it
thereafter, having quiesced OpenFirmware. Haven't we already been
working on unifying this between SPARC and PowerPC kernels?

I definitely don't think we need to play these tricks to keep
OpenFirmware resident while the kernel is running. Take a look at your
second patch -- it's _all_ just lookups in the device-tree, and you're
inventing a new way to do it instead of using the existing one.

-- 
dwmw2

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