Re: Can I/OAT DMA engineer access PCI MMIO space

[Dan Williams]

[ adding Dave ]

On 5/5/2011 1:45 AM, ååæ wrote:
> 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.

Ah ok, this is expected with the current upstream ioatdma driver.  The 
driver assumes that all transfers are mem-to-mem (ASYNC_TX_DMA or 
NET_DMA) and that a destination address error is a fatal error (similar 
to a kernel page fault).

With NTB, where failures are expected, the driver would need to be 
modified to expect the error, recover from it, and report it to the 
application.

> What does dma-slave mean? Just like DMA_SLAVE flag existing in other DMA
> drivers?

Yes, DMA_SLAVE is the generic framework to associate a dma offload 
device with an mmio peripheral.

--
Dan
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