linux-kernel - Re: BUG in drivers/dma/ioat/dma

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Date:	Tue, 29 Jun 2010 16:57:45 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Chris Li <lkml@...isli.org>
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: BUG in drivers/dma/ioat/dma_v2.c:314

On 6/29/2010 4:20 PM, Chris Li wrote:
> On Mon, Jun 28, 2010 at 5:45 PM, Dan Williams<dan.j.williams@...el.com>  wrote:
>> Looks like that dev_err() did not make it to the console.  The attached
>> patch should get us some more debug information.  This will stop the driver
>> from making forward progress (applies to current -git).  I suspect this may
>> be triggering from the driver self test, but to be safe you should set
>> CONFIG_NET_DMA=n and CONFIG_ASYNC_TX_DMA=n.
>
> OK, with the patch it does not kernel panic any more.
>
> Here is the prink from ioatdma.
>

Thanks.

[..]
> 0000:00:0f.0: ioat2_timer_event: Channel halted (10)

This says that we got an invalid chain address error when trying to 
start the engine.  If there was a driver problem with init I would have 
expected to see reports from other systems.  The attached patch will 
print out what chain address we are setting.  The hardware expects a 
64-byte aligned address which should be guaranteed by the use of 
pci_pool_alloc().

However, if you are up for another experiment, I'd like to see what 
happens if you disable VT-d.  Maybe it is a misconfigured iommu table 
that is blocking the engine's access to memory?

> I attach the full dmesg in case you need it. Is it possible that
> the Mac Pro is MSI only and ioatdma is not happy about that?

Not really, MSI is the preferred mode of operation, and as I said 
earlier if something like this were broken I would expect reports from 
other platforms??

--
Dan

View attachment "report-chainaddr.patch" of type "text/plain" (516 bytes)