PCI/MSI: Export pci_msix_prepare_desc() for dynamic MSI-X allocations

JIRA: https://issues.redhat.com/browse/RHEL-109583

commit 5da8a8b
Author: Shradha Gupta <shradhagupta@linux.microsoft.com>
Date:   Wed Jun 11 07:10:01 2025 -0700

    PCI/MSI: Export pci_msix_prepare_desc() for dynamic MSI-X allocations

    For supporting dynamic MSI-X vector allocation by PCI controllers, enabling
    the flag MSI_FLAG_PCI_MSIX_ALLOC_DYN is not enough, msix_prepare_msi_desc()
    to prepare the MSI descriptor is also needed.

    Export pci_msix_prepare_desc() to allow PCI controllers to support dynamic
    MSI-X vector allocation.

    Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
    Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    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/msi/irqdomain.c

@@ -202,13 +202,14 @@ static void pci_irq_unmask_msix(struct irq_data *data)
 	pci_msix_unmask(irq_data_get_msi_desc(data));
 }
 
-static void pci_msix_prepare_desc(struct irq_domain *domain, msi_alloc_info_t *arg,
-				  struct msi_desc *desc)
+void pci_msix_prepare_desc(struct irq_domain *domain, msi_alloc_info_t *arg,
+			   struct msi_desc *desc)
 {
 	/* Don't fiddle with preallocated MSI descriptors */
 	if (!desc->pci.mask_base)
 		msix_prepare_msi_desc(to_pci_dev(desc->dev), desc);
 }
+EXPORT_SYMBOL_GPL(pci_msix_prepare_desc);
 
 static const struct msi_domain_template pci_msix_template = {
 	.chip = {

include/linux/msi.h

@@ -674,6 +674,8 @@ struct irq_domain *pci_msi_create_irq_domain(struct fwnode_handle *fwnode,
 					     struct irq_domain *parent);
 u32 pci_msi_domain_get_msi_rid(struct irq_domain *domain, struct pci_dev *pdev);
 struct irq_domain *pci_msi_get_device_domain(struct pci_dev *pdev);
+void pci_msix_prepare_desc(struct irq_domain *domain, msi_alloc_info_t *arg,
+			   struct msi_desc *desc);
 #else /* CONFIG_PCI_MSI */
 static inline struct irq_domain *pci_msi_get_device_domain(struct pci_dev *pdev)
 {