linux-kernel - Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit

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Date:	Wed, 27 May 2009 14:05:42 -0500
From:	Becky Bruce <beckyb@...nel.crashing.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	jeremy@...p.org, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, Ian.Campbell@...rix.com
Subject: Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit


On May 22, 2009, at 5:51 AM, FUJITA Tomonori wrote:

> On Thu, 21 May 2009 13:18:54 -0700
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
>> Becky Bruce wrote:
>>> I can work with that, but it's going to be a bit inefficient, as I
>>> actually need the dma_addr_t, not the phys_addr_t, so I'll have to
>>> convert.  In every case, this is a conversion I've already done and
>>> that I need in the calling code as well.  Can we pass in both the
>>> phys_addr_t and the dma_addr_t?
>>
>> The Xen implementation would needs to do the phys to bus conversion  
>> page
>> by page anyway, so it wouldn't help much.  But it also wouldn't hurt.
>>
>> How expensive is the phys-to-bus conversion on power?  Is it worth
>> making the interface more complex for?  Would passing phys+bus mean  
>> that
>> we wouldn't also need to pass dev?
>
> I don't think so. POWERPC needs it.

Hrm, it looks like my response to this got dropped.  Fujita is correct  
- we still need the dev on powerpc because we use it to get device- 
specific information that is used to determining when we need to  
actually bounce.

Cheers,
B

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