linux-kernel - Re: dma api errors with swiotlb

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Date:   Wed, 4 Sep 2019 15:21:55 +0200
From:   Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: dma api errors with swiotlb

On 9/4/19 3:16 PM, Christoph Hellwig wrote:
> On Wed, Sep 04, 2019 at 03:02:14PM +0200, Thomas Hellström (VMware) wrote:
>> It looks like it does that, although when we send it, the SWIOTLB error has
>> already occured and been printed out, and then the sequence starts again.
> Well, the only way to really find out is to try.  We also have a
> backoff algorithm in the SCSI midlayer, so it should not be much of
> an inpact.  If you care about the warnings they can be disabled using
> DMA_ATTR_NO_WARN.  I have to admit that I'm not even sure the warnings
> are all that useful, but that's something you need to take up with
> the swiotlb maintainer.

Yes, I guess so. I actually think the warnings make sense, since while 
the scsi midlayer handles this nicely, other drivers competing for the 
space might not.

Thanks!
Thomas