nvmet: pci-epf: do not fall back to using INTX if not supported

Some endpoint PCIe controllers do not support raising legacy INTX
interrupts. This support is indicated by the intx_capable field of
struct pci_epc_features. Modify nvmet_pci_epf_raise_irq() to not
automatically fallback to trying raising an INTX interrupt after an MSI
or MSI-X error if the controller does not support INTX.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

Author: damien-lemoal

drivers/nvme/target/pci-epf.c

@@ -636,14 +636,16 @@ static void nvmet_pci_epf_raise_irq(struct nvmet_pci_epf_ctrl *ctrl,
 	switch (nvme_epf->irq_type) {
 	case PCI_IRQ_MSIX:
 	case PCI_IRQ_MSI:
+		/*
+		 * If we fail to raise an MSI or MSI-X interrupt, it is likely
+		 * because the host is using legacy INTX IRQs (e.g. BIOS,
+		 * grub), but we can fallback to the INTX type only if the
+		 * endpoint controller supports this type.
+		 */
 		ret = pci_epc_raise_irq(epf->epc, epf->func_no, epf->vfunc_no,
 					nvme_epf->irq_type, cq->vector + 1);
-		if (!ret)
+		if (!ret || !nvme_epf->epc_features->intx_capable)
 			break;
-		/*
-		 * If we got an error, it is likely because the host is using
-		 * legacy IRQs (e.g. BIOS, grub).
-		 */
 		fallthrough;
 	case PCI_IRQ_INTX:
 		ret = pci_epc_raise_irq(epf->epc, epf->func_no, epf->vfunc_no,