linux-kernel - Re: [PATCH 1/2] add phys_addr_t for holding physical addresses

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Date:	Mon, 11 Aug 2008 15:15:07 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	benh@...nel.crashing.org
CC:	Andrew Morton <akpm@...ux-foundation.org>, ehabkost@...hat.com,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 1/2] add phys_addr_t for holding physical addresses

Benjamin Herrenschmidt wrote:
> On Mon, 2008-08-11 at 12:38 -0700, Jeremy Fitzhardinge wrote:
>   
>> Add a kernel-wide "phys_addr_t" which is guaranteed to be able to hold
>> any physical address.  By default it equals the word size of the
>> architecture, but a 32-bit architecture can set ARCH_PHYS_ADDR_T_64BIT
>> if it needs a 64-bit phys_addr_t.
>>     
>
> I've been wondering for some time why can't we make phys_addr_t and
> resource_size_t the same thing... I don't like having two ARCH_* thing
> especially since I believe the one for resources is already what we
> want.
>   

I made the same argument, but Andrew thinks they're conceptually 
distinct.  It is theoretically possible you might have a system with >4G 
memory, but all io resources < 4G, so you'd have resource_size_t 
32-bits, while having 64-bit physical addresses.  You can configure such 
a thing, but I don't know if it's 1) useful or 2) used.

    J
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