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

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Date:	Sun, 24 May 2009 00:59:26 +0200
From:	Leon Woestenberg <leon.woestenberg@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ian Campbell <Ian.Campbell@...citrix.com>,
	Becky Bruce <beckyb@...nel.crashing.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	"linuxppc-dev@...abs.org" <linuxppc-dev@...abs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 2/3] powerpc: Add support for swiotlb on 32-bit

Hello,

On Sat, May 23, 2009 at 1:55 AM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> Ian Campbell wrote:
>>
>> On Thu, 2009-05-21 at 14:27 -0400, 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.
>>
>> Does
>>
>>    dma_addr_t dma_map_range(struct device *hwdev, phys_addr_t addr,
>>    size_t size);
>>
>> work for you?
>>
>> If the range does not need mapping then it returns the dma address, if
>> you needed to calculate the dma address anyway to figure out if mapping
>> is required then this is fine. If the range does need mapping then it
>> returns NULL.
>>
>
> My only concern is whether dma_addr_t == 0 is actually equivalent to NULL.
>  That is, can we be sure that address 0 will never be used?
>
Indeed, I remember seeing 0 returned on pci_alloc_coherent() as an
address (cookie).

Regards,
-- 
Leon
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