Re: [Xen-devel] Re: PCI passthrough stopped working, brainache!

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2011-10-15 at 11:07 +0100, Andy Burns wrote:
> On 13 October 2011 19:15, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> wrote:
> 
> > On Wed, Oct 12, 2011 at 10:36:12PM +0100, Andy Burns wrote:
> >
> >> I discovered that the PCI tuners don't work in dom0 under Xen,
> >> they only work if the dom0 is booted  as baremetal.
> >
> > That would imply it is not the PCI passthrough code (good!).
> > It is something related to the driver
> 
> I've been having a go at getting the card running in dom0 rather than
> domU, no more success yet.
> 
> I've stopped using the PCI resource realignment for now, and enabled
> debugging knobs in the tuner modules, seems the I2C transfers used to
> program the tuner and receive status bits back from it are working OK,
> I can see the driver queueing up DMA using a succession of transfer
> buffers, and apparently interrupts signalling their completion.
> 
> Presume it's correct that within the dom0, the buffers should *NOT* be
> within the SWIOTLB range?

In general if a driver is correctly using the DMA API things should
never be within the swiotlb.

[...]
> Hypervisor, dom0 (and domU when I was using it) are all 64bit, the
> tuner device is 32bit, is this likely to be an issue with DMA
> transfers? Any extra logging for Xen?

I think you've got 8G of RAM so one thing which might be worth trying is
to give "mem=2G" (or perhaps 3G) on the hypervisor command line. That
ought to rule out addresses which are too high. (just a datapoint, not a
solution)

I wonder if the hypervisor's "dma_bits" option has any relevance here?
Might be worth a go?

For a domU (but not dom0, AFAICT) you can limit the machine addresses
allocated to a guest using "machine_address_size" in the cfg file. Only
seems to be supported by xend and not xl at the moment. That might be
another worthwhile experiment.

> > I saw something about I2C, is there a knob in the driver to _not_ use I2C?
> 
> Not for my tuner

In general I think these sorts cards use I2C extensively, i.e. the tuner
etc is on an i2c bus, so I wouldn't expect anything to work at all
without it.

Ian.



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