Re: [Qemu-devel] [PATCH 2/3] VFIO driver for mediated PCI device

[Kirti Wankhede]

On 6/25/2016 1:15 AM, Alex Williamson wrote:
> On Sat, 25 Jun 2016 00:04:27 +0530
> Kirti Wankhede <address@hidden> wrote:
> 

>>>> +
>>>> +static int mdev_get_irq_count(struct vfio_mdev *vmdev, int irq_type)
>>>> +{
>>>> +  /* Don't support MSIX for now */
>>>> +  if (irq_type == VFIO_PCI_MSIX_IRQ_INDEX)
>>>> +          return -1;
>>>> +
>>>> +  return 1;  
>>>
>>> Too much hard coding here, the mediated driver should define this.
>>>   
>>
>> I'm testing INTX and MSI, I don't have a way to test MSIX for now. So we
>> thought we can add supported for MSIX later. Till then hard code it to 1.
> 
> To me it screams that there needs to be an interface to the mediated
> device here.  How do you even know that the mediated device intends to
> support MSI?  What if it wants to emulated a VF and not support INTx?
> This is basically just a big "TODO" flag that needs to be addressed
> before a non-RFC.
> 

VFIO user space app reads emulated PCI config space of mediated device.
In PCI capability list when MSI capability (PCI_CAP_ID_MSI) is present,
it calls VFIO_DEVICE_SET_IRQS ioctl with irq_set->index set to
VFIO_PCI_MSI_IRQ_INDEX.
Similarly, MSIX is identified from emulated config space of mediated
device that checks if MSI capability is present and number of vectors
extracted from PCI_MSI_FLAGS_QSIZE flag.
vfio_mpci modules don't need to query it from vendor driver of mediated
device. Depending on which interrupt to support, mediated driver should
emulate PCI config space.

Thanks,
Kirti.