linux-kernel - Re: [PATCH 1/6] rapidio: add common mapping APIs for RapidIO memory access

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Date:	Fri, 12 Jun 2009 08:58:49 -0500
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Li Yang <leoli@...escale.com>
Cc:	akpm@...ux-foundation.org, davem@...emloft.net,
	mporter@...nel.crashing.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, netdev@...r.kernel.org,
	Zhang Wei <zw@...kernel.org>
Subject: Re: [PATCH 1/6] rapidio: add common mapping APIs for RapidIO memory  access


On Jun 12, 2009, at 8:27 AM, Li Yang wrote:

> On Thu, Jun 11, 2009 at 9:32 PM, Kumar  
> Gala<galak@...nel.crashing.org> wrote:
>>
>> On Jun 11, 2009, at 4:47 AM, Li Yang-R58472 wrote:
>>
>>>> On May 12, 2009, at 3:35 AM, Li Yang wrote:
>>>>
>>>>> Add the mapping functions used to support direct IO memory  
>>>>> access of
>>>>> rapidIO.
>>>>>
>>>>> Signed-off-by: Zhang Wei <zw@...kernel.org>
>>>>> Signed-off-by: Li Yang <leoli@...escale.com>
>>>>
>>>> Use inbnd/outbnd instead of inb/outb which make one think of
>>>> byte level io accessors.
>>>>
>>>> As I look at this I don't think this is the correct API.  I
>>>> think we should be using the DMA mapping API to hide these
>>>> details.  The concept of mapping like this seems to be more a
>>>> function of FSL's Address translation/mapping unit (ATMU) than
>>>> anything specific to the RIO bus standard.
>>>
>>> This is a separate RIO block level ATMU.  Although it looks like the
>>> system level ATMU, system ATMU doesn't have the knowledge of rapidIO
>>> target device ID.  The mapping need to be dynamic, as it's easy to  
>>> have
>>> more RIO devices than the outbound windows.
>>
>> I understand that.  What I'm saying is the RIO block level ATMU is a
>> Freescale specific detail and not part of any standard RIO bus  
>> programming
>> model.  We have mapping APIs that we can connect to for this via  
>> the DMA API
>> layer.
>
> Ok, I see your point now. Do you mean dma_map_*() for DMA API layer?
> But in my understanding the current dma_map_*() APIs are preparing
> local memory for device to access which is similar to the inbound
> case.  Is it suitable to also use them for mapping device's space for
> CPU access?  Can you give an example of using this API for Address
> Translation and Mapping purpose?

Yes, I meant the dma_map_*() API.  Any system with a true IOMMU uses  
the dma_map_ layer as the way to do address translation.

- k
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