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

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Date:	Fri, 12 Jun 2009 21:27:58 +0800
From:	Li Yang <leoli@...escale.com>
To:	Kumar Gala <galak@...nel.crashing.org>
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 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?

- Leo
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