PCI: Add support for DMA alias quirks

Some devices are broken and use a requester ID other than their physical
devfn.  Add a byte, using an existing gap in the pci_dev structure, to
store an alternate "alias" devfn.  A bit in the dev_flags tells us when
this is valid.  We then add the alias as one more step in the
pci_for_each_dma_alias() iterator.
Tested-by: George Spelvin <linux@horizon.com>
Tested-by: Pat Erley <pat-lkml@erley.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/search.c

@@ -37,6 +37,17 @@ int pci_for_each_dma_alias(struct pci_dev *pdev,
 	if (ret)
 		return ret;
 
+	/*
+	 * If the device is broken and uses an alias requester ID for
+	 * DMA, iterate over that too.
+	 */
+	if (unlikely(pdev->dev_flags & PCI_DEV_FLAGS_DMA_ALIAS_DEVFN)) {
+		ret = fn(pdev, PCI_DEVID(pdev->bus->number,
+					 pdev->dma_alias_devfn), data);
+		if (ret)
+			return ret;
+	}
+
 	for (bus = pdev->bus; !pci_is_root_bus(bus); bus = bus->parent) {
 		struct pci_dev *tmp;
 

include/linux/pci.h

@@ -171,6 +171,8 @@ enum pci_dev_flags {
 	PCI_DEV_FLAGS_ASSIGNED = (__force pci_dev_flags_t) (1 << 2),
 	/* Flag for quirk use to store if quirk-specific ACS is enabled */
 	PCI_DEV_FLAGS_ACS_ENABLED_QUIRK = (__force pci_dev_flags_t) (1 << 3),
+	/* Flag to indicate the device uses dma_alias_devfn */
+	PCI_DEV_FLAGS_DMA_ALIAS_DEVFN = (__force pci_dev_flags_t) (1 << 4),
 };
 
 enum pci_irq_reroute_variant {
@@ -268,6 +270,7 @@ struct pci_dev {
 	u8		rom_base_reg;	/* which config register controls the ROM */
 	u8		pin;		/* which interrupt pin this device uses */
 	u16		pcie_flags_reg;	/* cached PCIe Capabilities Register */
+	u8		dma_alias_devfn;/* devfn of DMA alias, if any */
 
 	struct pci_driver *driver;	/* which driver has allocated this device */
 	u64		dma_mask;	/* Mask of the bits of bus address this