linux-kernel - Re: [PATCH] of: specify initrd location using 64-bit

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Date:	Thu, 13 Sep 2012 16:02:49 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	Cyril Chemparathy <cyril@...com>, linux-mips@...ux-mips.org,
	x86@...nel.org, a-jacquiot@...com, mahesh@...ux.vnet.ibm.com,
	linus.walleij@...aro.org, grant.likely@...retlab.ca,
	paul.gortmaker@...driver.com, paulus@...ba.org, hpa@...or.com,
	m.szyprowski@...sung.com, jonas@...thpole.se,
	linux@....linux.org.uk, linux-c6x-dev@...ux-c6x.org,
	nico@...aro.org, david.daney@...ium.com, mingo@...hat.com,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	benh@...nel.crashing.org, suzuki@...ibm.com, linux@...nrisc.net,
	arnd@...db.de, microblaze-uclinux@...e.uq.edu.au,
	devicetree-discuss@...ts.ozlabs.org, msalter@...hat.com,
	rob.herring@...xeda.com, tglx@...utronix.de,
	linux-arm-kernel@...ts.infradead.org, blogic@...nwrt.org,
	dhowells@...hat.com, monstr@...str.eu,
	linux-kernel@...r.kernel.org, ralf@...ux-mips.org, tj@...nel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] of: specify initrd location using 64-bit

On 09/13/2012 01:47 AM, Sebastian Andrzej Siewior wrote:
> On 09/13/2012 12:08 AM, Rob Herring wrote:
>>> Geert is right here. If it is a physical address, it should be
>>> phys_addr_t.
>>
>> While generally true, for the DT specific code I think it should be a
>> fixed u64. The size of the address is defined by the FDT, not the
>> kernel. It is very likely we could have a FDT that specifies addresses
>> in 64-bit values, but then we boot a kernel is compiled for !LPAE.
>> phys_addr_t is currently sized based on LPAE setting.
> 
> If your kernel is 32bit without PAE and your DTB address is >32ibt than
> you can't handle it. If you don't notice this in your dt code than you
> remap the wrong memory ioremap().

The size of the initrd fields are set by #address-cells properties and
determined when you create the dtb. The address to load the initrd is
decided by the bootloader/user and set at that point later in time. The
dtb should not be tied to the kernel you are booting. Obviously, if you
want to boot a non-PAE kernel, everything has to be placed at <4GB.

I can boot i386 and i386-pae kernels on an i386-pae machines. I expect
to generally be able to do that on ARM. Perhaps some SOCs like this one
will not allow that, it is not always true.

Rob

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