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Re: [Xen-users] Issues Booting DomU on TI DRA72 Chip

On Mon, 2015-07-13 at 08:33 -0400, Brandon Perez wrote:
> On 07/13/2015 04:29 AM, Ian Campbell wrote:
> > On Fri, 2015-07-10 at 11:21 -0400, Brandon Perez wrote:
> >
> > Is there a 1:1 mapping between (active) interrupts handled by this
> > cascaded controller a SPIs? i.e. if there were 32 interrupts but only 16
> > SPIs would you only be able to use 16 of the devices?
> >
> > Or does it support multiple interrupt sources triggering a single SPI?
>      For the chip I'm working with, it only supports a 1:1 mapping. It 
> doesn't allow for multiple interrupts to share an SPI line.

This simplifies things somewhat for passthrough then, I think. You
simply leave routing and assignment of interrupts to SPIs in the hands
of dom0, and on passthrough it would pass the SPI to the guest with
appropriate values for the interrupt-parent and interrupts properties.

> > Right, this is a tricky one. Other than various solutions involving
> > trusting the firmware to get it right and requiring dom0 to not muck
> > around with it the only other solution I can think of would be a bit of
> > code in Xen which traps dom0's attempted changes and validates them,
> > preventing dom0 from mucking with the ones Xen cares about.
> >
> > Given how simple these sorts of interrupt remappers often are that might
> > not even be that much code.
> >
> > Ian.
> >
>      I think that wouldn't be too difficult to do, but for now, I'm 
> going to stick with using the device tree to inform Xen and the Kernel.


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