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

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Message-ID: <20110201103617.2c3aa118@debxo>
Date:	Tue, 1 Feb 2011 10:36:17 -0800
From:	Andres Salomon <dilinger@...ued.net>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Daniel Drake <dsd@...top.org>,
	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

On Tue, 01 Feb 2011 14:21:22 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> 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?
> 

That is unclear.  For now, it's not, and there aren't plans to make it
so.

> > 
> > 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?

No.

> - variable initial_boot_params should be NULL in your case, right?

Yes.

> - 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 ...

Perhaps it should be specifically checking for a fdt (by way of
initial_boot_params)?   Sparc also does not have initial_boot_params,
so one might even be able to drop an #ifdef in the process.
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