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SubjectRe: [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@linutronix.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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