[PATCH] vfio/pci: Skip enabling INTx if the IRQ line is also unassgined

[Shivaprasad G Bhat <sbhat@linux.ibm.com>]

Currently, the PCI_INTERRUPT_PIN alone is checked before enabling
the INTx. Its also necessary to have the IRQ Lines assigned for
the INTx to work. So, check the PCI_INTERRUPT_LINE against 0xff
indicates no connection.

The problem was observed on Power10 systems which primarily use
MSI-X, and LSI lines are not connected on all devices under a
PCIe switch. In this configuration where the PIN is non-zero
but the LINE was 0xff, the VFIO_DEVICE_SET_IRQS was failing as
it was trying to map the irqfd for the LSI of the device.

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
---
 hw/vfio/pci.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index ab17a98ee5..69a519d143 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -264,12 +264,12 @@ static void vfio_irqchip_change(Notifier *notify, void *data)
 static bool vfio_intx_enable(VFIOPCIDevice *vdev, Error **errp)
 {
     uint8_t pin = vfio_pci_read_config(&vdev->pdev, PCI_INTERRUPT_PIN, 1);
+    uint8_t line = vfio_pci_read_config(&vdev->pdev, PCI_INTERRUPT_LINE, 1);
     Error *err = NULL;
     int32_t fd;
     int ret;
 
-
-    if (!pin) {
+    if (!pin || (line == 0xFF)) {
         return true;
     }