PCI: Introduce pci_real_dma_dev()

The current DMA alias implementation requires the aliased device be on the
same PCI bus as the requester ID.  Add an arch-specific mechanism to point
to another PCI device when doing mapping and PCI DMA alias search.  The
default case returns the actual device.

Link: https://lore.kernel.org/r/1579613871-301529-4-git-send-email-jonathan.derrick@intel.com
Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Christoph Hellwig <hch@lst.de>

arch/x86/pci/common.c

@@ -736,3 +736,13 @@ int pci_ext_cfg_avail(void)
 	else
 		return 0;
 }
+
+#if IS_ENABLED(CONFIG_VMD)
+struct pci_dev *pci_real_dma_dev(struct pci_dev *dev)
+{
+	if (is_vmd(dev->bus))
+		return to_pci_sysdata(dev->bus)->vmd_dev;
+
+	return dev;
+}
+#endif

drivers/pci/pci.c

@@ -6033,7 +6033,9 @@ bool pci_devs_are_dma_aliases(struct pci_dev *dev1, struct pci_dev *dev2)
 	return (dev1->dma_alias_mask &&
 		test_bit(dev2->devfn, dev1->dma_alias_mask)) ||
 	       (dev2->dma_alias_mask &&
-		test_bit(dev1->devfn, dev2->dma_alias_mask));
+		test_bit(dev1->devfn, dev2->dma_alias_mask)) ||
+	       pci_real_dma_dev(dev1) == dev2 ||
+	       pci_real_dma_dev(dev2) == dev1;
 }
 
 bool pci_device_is_present(struct pci_dev *pdev)
@@ -6057,6 +6059,21 @@ void pci_ignore_hotplug(struct pci_dev *dev)
 }
 EXPORT_SYMBOL_GPL(pci_ignore_hotplug);
 
+/**
+ * pci_real_dma_dev - Get PCI DMA device for PCI device
+ * @dev: the PCI device that may have a PCI DMA alias
+ *
+ * Permits the platform to provide architecture-specific functionality to
+ * devices needing to alias DMA to another PCI device on another PCI bus. If
+ * the PCI device is on the same bus, it is recommended to use
+ * pci_add_dma_alias(). This is the default implementation. Architecture
+ * implementations can override this.
+ */
+struct pci_dev __weak *pci_real_dma_dev(struct pci_dev *dev)
+{
+	return dev;
+}
+
 resource_size_t __weak pcibios_default_alignment(void)
 {
 	return 0;

drivers/pci/search.c

@@ -32,6 +32,12 @@ int pci_for_each_dma_alias(struct pci_dev *pdev,
 	struct pci_bus *bus;
 	int ret;
 
+	/*
+	 * The device may have an explicit alias requester ID for DMA where the
+	 * requester is on another PCI bus.
+	 */
+	pdev = pci_real_dma_dev(pdev);
+
 	ret = fn(pdev, pci_dev_id(pdev), data);
 	if (ret)
 		return ret;

include/linux/pci.h

@@ -1202,6 +1202,7 @@ int __must_check pci_resize_resource(struct pci_dev *dev, int i, int size);
 int pci_select_bars(struct pci_dev *dev, unsigned long flags);
 bool pci_device_is_present(struct pci_dev *pdev);
 void pci_ignore_hotplug(struct pci_dev *dev);
+struct pci_dev *pci_real_dma_dev(struct pci_dev *dev);
 
 int __printf(6, 7) pci_request_irq(struct pci_dev *dev, unsigned int nr,
 		irq_handler_t handler, irq_handler_t thread_fn, void *dev_id,