linux-kernel - Re: [PATCH v2 01/15] x86/e820: remove conditional early mapping in parse_e820

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Message-ID: <4D4808D2.3080701@linutronix.de>
Date:	Tue, 01 Feb 2011 14:21:22 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Daniel Drake <dsd@...top.org>
CC:	Andres Salomon <dilinger@...ued.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-kernel@...r.kernel.org, sodaville@...utronix.de,
	x86@...nel.org, dirk.brandewie@...il.com
Subject: Re: [PATCH v2 01/15] x86/e820: remove conditional early mapping in
 parse_e820_ext

Daniel Drake wrote:
> Hi,
Hi,

> Context: https://patchwork.kernel.org/patch/450681/
> 
> This patch will indeed cause problems for OLPC. Thanks for bringing it
> to our attention.
> 
> On OLPC, the device tree is not used as a source of devices like on
> other platforms, it is simply used to present information to the
> kernel and userspace (in read-only fashion).
> 
> If I understand it correctly, the above patch is saying: if we have a
> device tree, don't add the standard x86 RTC device.
Yes.

> However, what we need it to say is: if we have a device tree *and* the
> device tree is being used as a source of devices, don't add the
> standard x86 RTC device.
> 
> Therefore in the OLPC case, this particular bail-out condition will
> never be met, because the device tree is not being used as a source of
> devices.
So it is not case now. Will it ever be?

> 
> Does that make sense?

I don't quite get how or what for do you use the device tree. Could you 
please answer me the following questions:
- is the variable allnodes NULL in your case?
- variable initial_boot_params should be NULL in your case, right?
- how should I checked for "device tree is being used as a source of
   devices"? The nodes on in the device tree are not probed unless one
   calls of_platform_bus_probe() with a few ids. However I do this now
   unconditionally which is not a problem unless you have a device tree ...

> Thanks,
> Daniel

Sebastian
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