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

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Message-ID: <20130626234704.GG3344@jonmason-lab>
Date:	Wed, 26 Jun 2013 16:47:04 -0700
From:	Jon Mason <jon.mason@...el.com>
To:	Dan Williams <djbw@...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 Thu, Jun 20, 2013 at 02:20:30PM -0700, Dan Williams wrote:
> 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?

It uses the callbacks.  I've change the code to use dma_find_channel,
and will push it for review as a RFC shortly.

Thanks,
Jon
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