linux-kernel - Re: [PATCH 4/7] swiotlb: Allow arch override of address_needs

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Date:	Wed, 08 Apr 2009 15:36:58 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	galak@...nel.crashing.org, hch@...radead.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	ian.campbell@...rix.com, beckyb@...nel.crashing.org
Subject: Re: [PATCH 4/7] swiotlb: Allow arch override of address_needs_mapping

FUJITA Tomonori wrote:
>> Some architectures need non-trivial bus<->phys conversion routines, etc, 
>>     
>
> Only Xen needs such conversion for swiotlb.
>   

Becky's patches of last week also added __weak annotations to 
swiotlb_bus_to_virt, virt_to_bus and bus_to_phys; added the hwdev 
parameter to swiotlb_bus_to_phys; and added a weak 
swiotlb_arch_address_needs_mapping.  I assume that was needed because 
powerpc needs non-trivial implementations for those functions.

>> so either we can require it that all architectures wishing to use 
>> swiotlb define these functions, or have weak default functions that can 
>> be overridden by architectures where necessary.
>>     
>
> Can you give an example? I don't think IA64, X86_64 or POWER (which
> will use swiotlb) need any __weak functions. If you say other archs
> could use swiotlb, please tell me how they need these __weak.
>   

As I said, Becky's patches added hooks in many of the places we added 
them for Xen.  I assume that's because powerpc needs them; I have not 
seen the arch/powerpc side of those changes.

    J
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