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

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Date:	Tue, 26 Jan 2010 12:11:34 -0800
From:	Abhijeet Dharmapurikar <adharmap@...eaurora.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	benh@...nel.crashing.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, dwalker@...eaurora.org,
	arnd@...db.de, akpm@...ux-foundation.org, mingo@...e.hu,
	joerg.roedel@....com, maciej.sosnowski@...el.com,
	dan.j.williams@...el.com, beckyb@...nel.crashing.org,
	yanghy@...fujitsu.com, linux-arch@...r.kernel.org,
	adharmap@...cinc.com
Subject: Re: [RFC PATCH] dma: Add barrierless dma mapping/unmapping api

FUJITA Tomonori wrote:
> On Tue, 26 Jan 2010 15:30:10 +1100
> Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
>> On Mon, 2010-01-25 at 18:35 -0800, adharmap@...eaurora.org wrote:
>>> From: Abhijeet Dharmapurikar <adharmap@...cinc.com>
>>>
  >
>> There are people nowadays putting AXI bridges and the whole ARM
>> paraphernalia of IP cores behind them on PowerPC cores for example and I
>> can see that happening with x86 as well.
>>
>> In your case, I believe your are fixing the wrong problem anyways. The
>> right approach would be instead to put all your buffer into an sglist
>> and use dma_map/unmap_sg().
> 
> Agreed again. That's exactly what I suggested before:
> 
> http://marc.info/?l=linux-kernel&m=126294076917753&w=2

I somehow missed your post, my apologies. Agreed that dma_map/unmap_sg 
would be the correct api to use here, however they still call the 
dmac_.*_range to map buffers. I could change those calls to do a barrier 
  only after mapping the last buffer. This would be much more cleaner 
than introducing a .*_nobarrier API.

Thanks for all the replies.

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