Date: Fri, 8 Jan 2010 17:52:20 +0900
To: adharmap@codeaurora.org
Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org
Subject: Re: RFC non barrier versions of dma_map functions 
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
In-Reply-To: <4B4279A1.4090706@codeaurora.org>
References: <4B4279A1.4090706@codeaurora.org>
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On Mon, 04 Jan 2010 15:28:33 -0800
Abhijeet Dharmapurikar <adharmap@codeaurora.org> wrote:

>    This is a request for extending the DMA api for efficient handling of 
> multiple buffers or scatter gather mapping/unmapping operations.
> 
>    I am based on an ARMv7 device and we have a situation where we need 
> to dma map multiple cached buffers for a single dma transaction.
> 
>    The current DMA api suggests the use of dma_map_single/ 
> dma_unmap_single for cache consistency. On ARMv7 it performs the 
> necessary cache-operations and calls data sync barrier instruction 
> (DSB). In our case we would be executing multiple DSB instructions
> before starting the dma operation - we need memory to be consistent
> only after we map the last buffer.

dma_map_sg? dma_map_sg requires the buffers to be consistent only
after it maps the last buffer, I think (I guess that you mean
'consistent' buffer is 'DMA ready' wrt cache).
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