linux-kernel - Re: [PATCH 2/2] ioatdma: add DMA

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Message-ID: <CAA9_cmdVfFmD5Li4b8WEtAiqCiSCKYuva_86MLV3ysAhyLXtig@mail.gmail.com>
Date:	Wed, 19 Jun 2013 11:56:38 -0700
From:	Dan Williams <djbw@...com>
To:	Jon Mason <jon.mason@...el.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ioatdma: add DMA_PRIVATE capabilities flag

On Wed, Jun 19, 2013 at 10:52 AM, Jon Mason <jon.mason@...el.com> wrote:
>> DMA_PRIVATE here keeps all channels private, so they couldn't be used
>> elsewhere, for example raid offload.  Do you need a private allocation
>> or can you get away with a dynamically assigned channel?
>
> I would like to have a dedicated DMA engine.  async_tx could cause the
> copies to complete out of order.  Do I need to add infrastructure to
> allow for private channel usage, and when unused allow the channel to
> be used by async_tx?

Can NTB just call dma_find_channel() once and be done?  Also, async_tx
will only get things out of order if you allow it to pick a new
channel for every operation, but as long as you specify a dependency
chain it will keep things in order (same as remembering the result of
dma_find_channel).

--
Dan
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