Re: IOMMU - DMA debugging

[Federico Vaga <federico.vaga-VIMSii5OdOuonA0d6jMUrA@public.gmane.org>]

On Wednesday, July 12, 2017 2:15:34 PM CEST Federico Vaga wrote:
> Thank you Robin
> 
> (inline comments)
> 
> On Wednesday, July 12, 2017 1:10:51 PM CEST Robin Murphy wrote:
> > On 12/07/17 08:11, Federico Vaga wrote:
> > > Hello,
> > > 
> > > kernel version 4.4.x
> > > 
> > > I'm facing an issue with the INTEL IOMMU driver and DMA mapping. I have
> > > an
> > > Ethernet driver that uses `dma_alloc_coherent()` to allocate and map
> > > some
> > > memory for DMA transfers.
> > 
> > Assuming 02:00.0 is your actual endpoint and not some upstream aliasing
> > bridge, is your driver definitely using the correct struct device
> > pointer corresponding to that for its DMA API calls?

I had a look at this point. The driver is using the device 02:08.0 (which is 
the one that should use) but the errors refers to the 02:00.0. I have a rough 
idea about how the IOMMU works but I do not know the details involved in the 
process.

\-[0000:00]-+-00.0
             +-01.0-[01-02]----00.0-[02]----08.0      <<<<<<<<<<
             +-01.1-[03]----00.0

Then among all the other devices, I have this from `dmesg`

[...]
[    2.212107] DMAR: Hardware identity mapping for device 0000:00:1f.3
[    2.219113] DMAR: Hardware identity mapping for device 0000:03:00.0
[    2.226118] DMAR: Hardware identity mapping for device 0000:04:00.0
[    2.233123] DMAR: Hardware identity mapping for device 0000:04:00.1
[...]
[    2.693295] iommu: Adding device 0000:00:1f.3 to group 22
[    2.699350] iommu: Adding device 0000:01:00.0 to group 23
[    2.705389] iommu: Adding device 0000:02:08.0 to group 23
[    2.711444] iommu: Adding device 0000:03:00.0 to group 24
[    2.717552] iommu: Adding device 0000:04:00.0 to group 25
[...]


It misses the message "Hardware identity mapping for device 0000:02:08.0". Is 
it possible that there is not a valid DMAR table?

-- 
Federico Vaga
http://www.federicovaga.it/