linux-kernel - Re: [PATCH 1/2] dmadevices: dma_sync

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Message-ID: <CAA9_cmehScXsCgxwTHxSJ-KXaa52itDoY+3j1Yajnpy-GFU7Hg@mail.gmail.com>
Date:	Thu, 20 Jun 2013 14:20:30 -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 1/2] dmadevices: dma_sync_wait undefined

On Wed, Jun 19, 2013 at 9:28 AM, Jon Mason <jon.mason@...el.com> wrote:
> On Tue, Jun 18, 2013 at 06:13:28PM -0700, Dan Williams wrote:
[..]
> NTB is currently using it to flush any pending DMAs.  This is needed
> to allow the DMA engine and the CPU to perform operations on the same
> "Memory Window".  Without this, it is possible for the operations to
> complete out of order, which is not a desired outcome for any network
> traffic over NTB.  CPU is preferred over DMA engine for small
> transfers.  Also, it provides an alternative for errors in the DMA
> engine copy process (e.g., DMA mapping, device_prep_dma_memcpy, and
> dmaengine_submit).

Ok there really isn't a better alternative, is NTB always polling or
does it also use completion callbacks?
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