linux-kernel - Re: [PATCH] arm/tegra: select AUTO

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Date:	Fri, 14 Oct 2011 09:44:34 -0700
From:	Olof Johansson <olof@...om.net>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Stephen Warren <swarren@...dia.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"Colin Cross (ccross@...roid.com)" <ccross@...roid.com>,
	Erik Gilling <konkers@...roid.com>
Subject: Re: [PATCH] arm/tegra: select AUTO_ZRELADDR by default

On Fri, Oct 14, 2011 at 9:27 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Friday 14 October 2011, Stephen Warren wrote:
>> Arnd Bergmann wrote at Friday, October 14, 2011 9:30 AM:
>> ...
>> > You mention that tegra30 will require AUTO_ZRELADDR.
>>
>> Well, just to be clear, here's the situation I think:
>>
>> Tegra20's SDRAM starts at physical address 0.
>>
>> Tegra30's SDRAM starts at physical address 2G.
>>
>> To support that, we could either:
>>
>> a) Introduce a new Kconfig variable for Tegra30, make T20/T30 mutually
>> exclusive, and update arch/arm/mach-tegra/Makefile.boot to set zreladdr
>> etc. based on the new Tegra30 config variable too. Then, there's no need
>> for AUTO_ZRELADDR anywhere.
>>
>> b) Have no new config variable, build a unified T20/T30 kernel, leave
>> Makefile.boot untouched, and rely on using AUTO_ZRELADDR for Tegra30 to
>> account for the different SDRAM physical addresses.
>
> Ok, thanks for the explanation, that makes it much clearer. For
> completeness, you could also do both of the above and make T20/T30 mutually
> exclusive unless AUTO_ZRELADDR is set. That might be more complex than
> necessary, I don't know.

That is likely to get messy.

Seems like there could be some use for a (silent) option for a
platform to indicate that it can do XIP kernel (or zImage), and thus
not able to use AUTO_ZRELADDR (or other options that require rewriting
text segment of zImage or kernel).

Language gets awkard though, since it'd be a negative option (or all
platforms would need to add it). MACH_XIP_UNSUPPORTED perhaps?


-Olof
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