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Subject: Re: [RFC PATCH v2 08/11] powerpc: gamecube/wii: early debugging
	using usbgecko
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Albert Herranz <albert_herranz@yahoo.es>
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Date: Mon, 30 Nov 2009 10:18:15 +1100
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On Sat, 2009-11-28 at 21:43 +0100, Albert Herranz wrote:
> +        * Prepare again the same BAT for MMU_init.
> +        * This allows udbg I/O to continue working after the MMU is
> +        * turned on for real.
> +        *
> +        * We are assuming here that exi_io_base is identity mapped.
> +        */
> +       addr = ((unsigned long)exi_io_base) & 0xffff0000;
> +       setbat(1, addr, addr, 128*1024, PAGE_KERNEL_NCG); 

How do you prevent that from overlapping otherwise valid kernel
mappings ?

You need to allocate the virtual space. For a debug thing like that, you
could use the fixmap. In fact, I think we should create a fixmap entry
or two always available for use by early debug.

Cheers,
Ben.