1 files changed, 22 insertions, 5 deletions

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 2225afc1cbbb..496ed9130600 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -1451,13 +1451,30 @@ struct irq_domain *pci_msi_create_irq_domain(struct fwnode_handle *fwnode,
 }
 EXPORT_SYMBOL_GPL(pci_msi_create_irq_domain);
 
+/*
+ * Users of the generic MSI infrastructure expect a device to have a single ID,
+ * so with DMA aliases we have to pick the least-worst compromise. Devices with
+ * DMA phantom functions tend to still emit MSIs from the real function number,
+ * so we ignore those and only consider topological aliases where either the
+ * alias device or RID appears on a different bus number. We also make the
+ * reasonable assumption that bridges are walked in an upstream direction (so
+ * the last one seen wins), and the much braver assumption that the most likely
+ * case is that of PCI->PCIe so we should always use the alias RID. This echoes
+ * the logic from intel_irq_remapping's set_msi_sid(), which presumably works
+ * well enough in practice; in the face of the horrible PCIe<->PCI-X conditions
+ * for taking ownership all we can really do is close our eyes and hope...
+ */
 static int get_msi_id_cb(struct pci_dev *pdev, u16 alias, void *data)
 {
         u32 *pa = data;
+        u8 bus = PCI_BUS_NUM(*pa);
+
+        if (pdev->bus->number != bus || PCI_BUS_NUM(alias) != bus)
+                *pa = alias;
 
-        *pa = alias;
         return 0;
 }
+
 /**
  * pci_msi_domain_get_msi_rid - Get the MSI requester id (RID)
  * @domain:     The interrupt domain
@@ -1471,7 +1488,7 @@ static int get_msi_id_cb(struct pci_dev *pdev, u16 alias, void *data)
 u32 pci_msi_domain_get_msi_rid(struct irq_domain *domain, struct pci_dev *pdev)
 {
         struct device_node *of_node;
-        u32 rid = 0;
+        u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
 
         pci_for_each_dma_alias(pdev, get_msi_id_cb, &rid);
 
@@ -1487,14 +1504,14 @@ u32 pci_msi_domain_get_msi_rid(struct irq_domain *domain, struct pci_dev *pdev)
  * @pdev:       The PCI device
  *
  * Use the firmware data to find a device-specific MSI domain
- * (i.e. not one that is ste as a default).
+ * (i.e. not one that is set as a default).
  *
- * Returns: The coresponding MSI domain or NULL if none has been found.
+ * Returns: The corresponding MSI domain or NULL if none has been found.
  */
 struct irq_domain *pci_msi_get_device_domain(struct pci_dev *pdev)
 {
         struct irq_domain *dom;
-        u32 rid = 0;
+        u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
 
         pci_for_each_dma_alias(pdev, get_msi_id_cb, &rid);
         dom = of_msi_map_get_device_domain(&pdev->dev, rid);