Re: [PATCH] vfio: pci: Advertise INTx only if LINE is connected

[Shivaprasad G Bhat]

On 3/18/25 11:28 PM, Alex Williamson wrote:
> On Tue, 18 Mar 2025 17:29:21 +0000
> Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx> wrote:
>
> > On POWER systems, when the device is behind the io expander,
> > not all PCI slots would have the PCI_INTERRUPT_LINE connected.
> > The firmware assigns a valid PCI_INTERRUPT_PIN though. In such
> > configuration, the irq_info ioctl currently advertizes the
> > irq count as 1 as the PCI_INTERRUPT_PIN is valid.
> >
> > The patch adds the additional check[1] if the irq is assigned
> > for the PIN which is done iff the LINE is connected.
> >
> > [1]: https://lore.kernel.org/qemu-devel/20250131150201.048aa3bf.alex.williamson@xxxxxxxxxx/
> >
> > Signed-off-by: Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx>
> > Suggested-By: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > ---
> >   drivers/vfio/pci/vfio_pci_core.c |    4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> > index 586e49efb81b..4ce70f05b4a8 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -734,6 +734,10 @@ static int vfio_pci_get_irq_count(struct vfio_pci_core_device *vdev, int irq_typ
> >   			return 0;
> >   
> >   		pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);
> > +#if IS_ENABLED(CONFIG_PPC64)
> > +		if (!vdev->pdev->irq)
> > +			pin = 0;
> > +#endif
> >   
> >   		return pin ? 1 : 0;
> >   	} else if (irq_type == VFIO_PCI_MSI_IRQ_INDEX) {
> See:
>
> https://lore.kernel.org/all/20250311230623.1264283-1-alex.williamson@xxxxxxxxxx/
>
> Do we need to expand that to test !vdev->pdev->irq in
> vfio_config_init()?

Yes. Looks to be the better option. I did try this and it works.


I see your patch has already got Reviewed-by. Are you planning

for v2 Or want me to post a separate patch with this new check?


> We don't allow a zero irq to be enabled in
> vfio_intx_enable(), so we might as well not report it as supported.

Yes. I agree.


Thank you!


Regards,

Shivaprasad