linux-kernel - Re: RFC non barrier versions of dma

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Message-Id: <20100108175201Z.fujita.tomonori@lab.ntt.co.jp>
Date:	Fri, 8 Jan 2010 17:52:20 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	adharmap@...eaurora.org
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: RFC non barrier versions of dma_map functions 

On Mon, 04 Jan 2010 15:28:33 -0800
Abhijeet Dharmapurikar <adharmap@...eaurora.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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