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

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 29 Jun 2016 00:15:23 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

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

Are you suggesting that if the user can determine which interrupts are
supported and the various counts for each by querying the PCI config
space of the mediated device then this interface should do the same,
much like vfio_pci_get_irq_count(), such that it can provide results
consistent with config space?  That I'm ok with.  Having the user find
one IRQ count as they read PCI config space and another via the vfio
API, I'm not ok with.  Thanks,

Alex