linux-kernel - Re: [PATCH 1/2] OLPC: Add support for calling into Open Firmware

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Date:	Mon, 21 Apr 2008 09:13:49 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mitch Bradley <wmb@...mworks.com>
CC:	Andres Salomon <dilinger@...ued.net>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joseph Fannin <jfannin@...il.com>,
	linux-kernel@...r.kernel.org, jordan.crouse@....com
Subject: Re: [PATCH 1/2] OLPC: Add support for calling into Open Firmware

Okay, stepping back a few steps, it's pretty clear that most of my 
objections aren't really an issue for Geode/OLPC; however, I *really* 
don't want others to pick it up as being "the" Open Firmware interface.

Within those constraints it makes sense to set up the PDEs in 
swapper_pg_dir and let them propagate using the normal mechanisms.

** This is assuming that your OF interface does not rely on a 1:1 
mapping of low memory being present at the time it makes a call.  If it 
*does*, then a separate page directory needs to be maintained for the OF 
class. **

Thus, I'm willing to accept this with these changes:

- Please name things specific to the interface (as opposed to Open 
Firmware in general, like the device tree) olpc_ofw or olpcfw, to denote 
that this is an OLPC-specific interface.  Thus, 
CONFIG_OLPC_OPEN_FIRMWARE or something along those lines.

- Make it explicit in Kconfig that OLPC_OPEN_FIRMWARE conflicts with 
X86_PAE, 64BIT, or X86_PAT.

- Change VMALLOC_END in include/asm-x86/pgtable_32.h so the kernel will 
know to avoid this virtual memory range.

- Add a memory region to arch/x86/mm/dump_tabletables.c.

	-hpa
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