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

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Date:	Tue, 1 Feb 2011 20:10:13 -0700
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Daniel Drake <dsd@...top.org>, 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, Feb 1, 2011 at 11:36 AM, Andres Salomon <dilinger@...ued.net> wrote:
> 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.

OLPC is very much the oddball in this case.  Everyone else uses
devicetree for registering devices.  It could be solved by making OLPC
explicitly register the RTC.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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