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

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Message-ID: <20130619201054.GA20996@jonmason-lab>
Date:	Wed, 19 Jun 2013 13:10:54 -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 2/2] ioatdma: add DMA_PRIVATE capabilities flag

On Wed, Jun 19, 2013 at 11:56:38AM -0700, Dan Williams wrote:
> 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).

Neither of these allow a device exclusive access to a channel.  Is
this not something that is desired by other users of DMA Engines, or
do I have a unique usage model?

Thanks,
Jon

> 
> --
> Dan
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