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

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Message-ID: <20130619175206.GA20737@jonmason-lab>
Date:	Wed, 19 Jun 2013 10:52:06 -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 Tue, Jun 18, 2013 at 05:59:59PM -0700, Dan Williams wrote:
> On Tue, Jun 18, 2013 at 5:46 PM, Jon Mason <jon.mason@...el.com> wrote:
> > Set the DMA_PRIVATE dma_transaction_type in the capability mask.  This
> > enables the ability to get an exclusive ioatdma DMA channel for any
> > devices that requests one via the dma_request_channel function call.
> >
> > Signed-off-by: Jon Mason <jon.mason@...el.com>
> > Acked-by: Dave Jiang <dave.jiang@...el.com>
> > ---
> >  drivers/dma/ioat/dma_v3.c |    1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/dma/ioat/dma_v3.c b/drivers/dma/ioat/dma_v3.c
> > index ca6ea9b..ac2aeef 100644
> > --- a/drivers/dma/ioat/dma_v3.c
> > +++ b/drivers/dma/ioat/dma_v3.c
> > @@ -1883,6 +1883,7 @@ int ioat3_dma_probe(struct ioatdma_device *device, int dca)
> >                 dma->copy_align = 6;
> >
> >         dma_cap_set(DMA_INTERRUPT, dma->cap_mask);
> > +       dma_cap_set(DMA_PRIVATE, dma->cap_mask);
> >         dma->device_prep_dma_interrupt = ioat3_prep_interrupt_lock;
> 
> 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?

Thanks,
Jon
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