linux-kernel - Re: [RFC PATCH] dma: Add barrierless dma mapping/unmapping api

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Date:	Tue, 26 Jan 2010 08:48:59 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	adharmap@...eaurora.org
Cc:	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	dwalker@...eaurora.org, Arnd Bergmann <arnd@...db.de>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Joerg Roedel <joerg.roedel@....com>,
	Maciej Sosnowski <maciej.sosnowski@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Becky Bruce <beckyb@...nel.crashing.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Yang Hongyang <yanghy@...fujitsu.com>,
	linux-arch@...r.kernel.org,
	Abhijeet Dharmapurikar <adharmap@...cinc.com>
Subject: Re: [RFC PATCH] dma: Add barrierless dma mapping/unmapping api

On Mon, 25 Jan 2010 18:35:46 -0800 adharmap@...eaurora.org wrote:

> From: Abhijeet Dharmapurikar <adharmap@...cinc.com>
> 
> Tests have shown that there is a significant performance gain
> when a driver uses mapping/unmapping functions without a barrier
> multiple times and calls dsb() only after the last buffer. This
> api adds support for barrierless dma operations on ARMv6
> and ARMv7.
> 
> Signed-off-by: Abhijeet Dharmapurikar <adharmap@...eaurora.org>
> ---
> 
> Please refer to the earlier post here http://lkml.org/lkml/2010/1/4/347. 
> These changes only are only for the arm v6 and v7
> architecture and introduce dma_map/unmap_single_nobarrier api.
> The idea is to extend the cpu_cache_fns.dma_.*_range functions to accept 
> a third boolean argument that tells it whether to execute the barrier or
> skip it. Note that this applies over Linux 2.6.33-rc5 and needs a few changes
> to apply on the linux-next tree.
> 
> 
>  arch/arm/include/asm/cacheflush.h  |   12 ++++----
>  arch/arm/include/asm/dma-mapping.h |   57 ++++++++++++++++++++++++++++++++++--
>  arch/arm/mm/cache-v6.S             |   15 ++++++----
>  arch/arm/mm/cache-v7.S             |   19 +++++++++++-
>  arch/arm/mm/dma-mapping.c          |   17 ++++++-----
>  drivers/staging/dream/pmem.c       |    4 +-
>  6 files changed, 97 insertions(+), 27 deletions(-)


Along with the other comments, the patch is also missing updates
to Documentation/DMA-API.txt ...


---
~Randy
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