linux-kernel - Re: wrong usage of MAX_DMA

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Date:	Tue, 30 Sep 2008 14:56:26 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Nicolas Pitre <nico@....org>
CC:	lkml <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: wrong usage of MAX_DMA_ADDRESS in bootmem.h

Nicolas Pitre wrote:
> I have implemented highmem for ARM.  To catch wrong usage of __pa() and 
>
> One issue is that bootmem.h uses __pa(MAX_DMA_ADDRESS). However 
> MAX_DMA_ADDRESS on ARM is defined as 0xffffffff because there is usually 
> no restriction on the maximum DMA-able address.
> 
> RMK suggested that those places should be using ISA_DMA_THRESHOLD 
> instead -- here's an excert of our conversation on this topic:
>

ok so do

#define MAX_DMA_ADDRESS ISA_DMA_THRESHOLD

 >> I suspect all those places which are doing __pa(MAX_DMA_ADDRESS) really
>> want to be using ISA_DMA_THRESHOLD - that's something to raise on LKML
>> if it's causing problems.

MAX_DMA_ADDRESS is the highest address used for ZONE_DMA / GFP_DMA

Does ISA_DMA_THRESHOLD have any meaning on ARM? If you use old ISA stuff then
you need CONFIG_ZONE_DMA and therefore also MAX_DMA_ADDRESS.

If not then there is no need to define CONFIG_ZONE_DMA and MAX_DMA_ADDRESS
looses its usual meaning.
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