Re: [Xen-devel] RFC: [PATCH 1/3] Enhance platform support for PCI

[Pranavkumar Sawargaonkar <psawargaonkar@xxxxxxx>]

Hi Julien,

On Thu, Feb 26, 2015 at 8:47 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> On 26/02/15 14:46, Pranavkumar Sawargaonkar wrote:
>> Hi
>
> Hi Pranavkumar,
>
>> Also if we just show only one vITS (or only one Virtual v2m frame)
>> instead of two vITS
>> then actual hardware interrupt number and virtual interrupt number
>> which guest will see will become different
>> This will hamper direct irq routing to guest.
>
> The IRQ injection should not consider a 1:1 mapping between pIRQ and vIRQ.

Yes, but in case of GICv2m( I am not sure about ITS) in register
MSI_SETSPI_NS device has to write the interrupt ID (which is pirq) to
generate an interrupt.
If you write virq which is different that pirq (associated with the
actual GICv2m frame ) then it will not trigger any interrupt.

Now there is case which I am not sure how it can be solvable with one
vITS/vGICv2m  -

. Suppose we have two GICv2m frames and say oneis  having an address
0x1000 for MSI_SETSPI_NS register and other 0x2000 for it's
MSI_SETSPI_NS register
. Assume first frame has SPI's (physical) 0x64 - 0x72 associated and
second has 0x80-0x88 associated.
. Now there are two PCIe hosts, first using first GICv2m frame as a
MSI parent and another using second frame.
. Device on first host uses MSI_SETSPI_NS (0x1000) address along with
a data (i.e. intr number say 0x64) and device on second host uses
0x2000 and data 0x80

Now if we show one vGICv2m frame in guest for both the devices then
what address I will program in each device's config space for MSI and
also what will the data value.
Secondly device's write for these addresses will be transparent to cpu
so how can we trap them while device wants to trigger any interrupt ?
Please correct me if I misunderstood anything.

Thanks,
Pranav



>
> I have a patch which allow virq != pirq:
>
> https://patches.linaro.org/43012/
>
> Regards,
>
> --
> Julien Grall

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