linux-kernel - Re: [PATCH v2 0/8] Improve performance of VM translation on x86

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Message-ID: <50783D16.5020309@intel.com>
Date:	Fri, 12 Oct 2012 08:53:58 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Konrad Rzeszutek Wilk <konrad@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v2 0/8] Improve performance of VM translation on x86_64

On 10/12/2012 08:15 AM, Andi Kleen wrote:
>> Could you also add  a blurb in the Documentation/< appropriate file
>> for device driver writes> mentioning the usage of __pa_symbol is
>> preferred?
> Device driver writer's shouldn't use any of this anyways, they should always
> use the PCI DMA APIs and never DMA to the stack or to static variables.
>
> -Andi

__pa_symbol is very architecture specific.  From what I can tell it only
exists for the x86 and mips architectures.  If a device driver is
expected to function on things such as PowerPC you cannot use it. 
Everything I have read indicates that for virtual to physical
translation in drivers it is preferred to use virt_to_phys, not __pa or
__pa_symbol.

Thanks,

Alex
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