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Date: Thu, 05 May 2011 16:45:58 +0800
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To: Dan Williams <dan.j.williams@intel.com>
CC: "Koul, Vinod" <vinod.koul@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Can I/OAT DMA engineer access PCI MMIO space
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于 2011年05月03日 23:58, Dan Williams 写道:
>
>> Do you mean that if I have mapped the mmio, I can' use I/OAT dma
>> transfer to this region any more?
>> I can use memcpy to copy data, but it consumes lots of cpu as PCI access
>> is too slow.
>> If I can use i/oat dma and asyc_tx api to do the job, the performance
>> should be imporved.
>> Thanks
>
>
> The async_tx api only supports memory-to-memory transfers.  To write 
> to mmio space with ioatdma you would need a custom method, like the 
> dma-slave support in other drivers, to program the descriptors with 
> the physical mmio bus address.
>
> -- 
> Dan
Thanks.
I directly read pci bar address and program it into descriptors, ioatdma 
works.
Some problem is, when PCI transfer failed (Using a NTB connect to 
another system, and the system power down),
ioatdma will cause kernel oops.

BUG_ON(is_ioat_bug(chanerr));
in drivers/dma/ioat/dma_v3.c, line 365

It seems that HW reports a 'IOAT_CHANERR_DEST_ADDR_ERR', and drivers 
can't recover from this situation.
What does dma-slave mean? Just like DMA_SLAVE flag existing in other DMA 
drivers?