PCI: hv: Allow dynamic MSI-X vector allocation

JIRA: https://issues.redhat.com/browse/RHEL-109580

commit ad518f2
Author: Shradha Gupta <shradhagupta@linux.microsoft.com>
Date:   Wed Jun 11 07:10:15 2025 -0700

    PCI: hv: Allow dynamic MSI-X vector allocation

    Allow dynamic MSI-X vector allocation for pci_hyperv PCI controller
    by adding support for the flag MSI_FLAG_PCI_MSIX_ALLOC_DYN and using
    pci_msix_prepare_desc() to prepare the MSI-X descriptors.

    Feature support added for both x86 and ARM64

    Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
    Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
    Reviewed-by: Saurabh Sengar <ssengar@linux.microsoft.com>
    Acked-by: Bjorn Helgaas <bhelgaas@google.com>

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Author: Maxim Levitsky

drivers/pci/controller/pci-hyperv.c

@@ -2061,6 +2061,7 @@ static struct irq_chip hv_msi_irq_chip = {
 static struct msi_domain_ops hv_msi_ops = {
 	.msi_prepare	= hv_msi_prepare,
 	.msi_free	= hv_msi_free,
+	.prepare_desc	= pci_msix_prepare_desc,
 };
 
 /**
@@ -2082,7 +2083,7 @@ static int hv_pcie_init_irq_domain(struct hv_pcibus_device *hbus)
 	hbus->msi_info.ops = &hv_msi_ops;
 	hbus->msi_info.flags = (MSI_FLAG_USE_DEF_DOM_OPS |
 		MSI_FLAG_USE_DEF_CHIP_OPS | MSI_FLAG_MULTI_PCI_MSI |
-		MSI_FLAG_PCI_MSIX);
+		MSI_FLAG_PCI_MSIX | MSI_FLAG_PCI_MSIX_ALLOC_DYN);
 	hbus->msi_info.handler = FLOW_HANDLER;
 	hbus->msi_info.handler_name = FLOW_NAME;
 	hbus->msi_info.data = hbus;