[PATCH v4 01/16] PCI: Add DMA alias iterator

[Alex Williamson <alex.williamson@redhat.com>]

In a mixed PCI/PCI-X/PCI-e topology, bridges can take ownership of
transactions, replacing the original requester ID with their own.
Sometimes we just want to know the resulting device or resulting
alias, sometimes we want each step in the chain.  This iterator
allows either usage.  When an endpoint is connected via an unbroken
chain of PCIe switches and root ports, it has no alias and its
requester ID is visible to the root bus.  When PCI/X get in the way,
we pick up aliases for bridges.

The reason why we potentially care about each step in the path is
because of PCI-X.  PCI-X has the concept of a requester ID, but
bridges may or may not take ownership of various types of
transactions.  We therefore leave it to the consumer of this function
to prune out what they don't care about rather than attempt to flatten
the alias ourselves.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/pci/search.c |   70 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pci.h  |    4 +++
 2 files changed, 74 insertions(+)

diff --git a/drivers/pci/search.c b/drivers/pci/search.c
index 4a1b972..5601cdb 100644
--- a/drivers/pci/search.c
+++ b/drivers/pci/search.c
@@ -18,6 +18,76 @@ DECLARE_RWSEM(pci_bus_sem);
 EXPORT_SYMBOL_GPL(pci_bus_sem);
 
 /*
+ * pci_for_each_dma_alias - Iterate over DMA aliases for a device
+ * @pdev: starting downstream device
+ * @fn: function to call for each alias
+ * @data: opaque data to pass to @fn
+ *
+ * Starting @pdev, walk up the bus calling @fn for each possible alias
+ * of @pdev at the root bus.
+ */
+int pci_for_each_dma_alias(struct pci_dev *pdev,
+			   int (*fn)(struct pci_dev *pdev,
+				     u16 alias, void *data), void *data)
+{
+	struct pci_bus *bus;
+	int ret;
+
+	ret = fn(pdev, PCI_DEVID(pdev->bus->number, pdev->devfn), data);
+	if (ret)
+		return ret;
+
+	for (bus = pdev->bus; !pci_is_root_bus(bus); bus = bus->parent) {
+		struct pci_dev *tmp;
+
+		/* Skip virtual buses */
+		if (!bus->self)
+			continue;
+
+		tmp = bus->self;
+
+		/*
+		 * PCIe-to-PCI/X bridges alias transactions from downstream
+		 * devices using the subordinate bus number (PCI Express to
+		 * PCI/PCI-X Bridge Spec, rev 1.0, sec 2.3).  For all cases
+		 * where the upstream bus is PCI/X we alias to the bridge
+		 * (there are various conditions in the previous reference
+		 * where the bridge may take ownership of transactions, even
+		 * when the secondary interface is PCI-X).
+		 */
+		if (pci_is_pcie(tmp)) {
+			switch (pci_pcie_type(tmp)) {
+			case PCI_EXP_TYPE_ROOT_PORT:
+			case PCI_EXP_TYPE_UPSTREAM:
+			case PCI_EXP_TYPE_DOWNSTREAM:
+				continue;
+			case PCI_EXP_TYPE_PCI_BRIDGE:
+				ret = fn(tmp,
+					 PCI_DEVID(tmp->subordinate->number,
+						   PCI_DEVFN(0, 0)), data);
+				if (ret)
+					return ret;
+				continue;
+			case PCI_EXP_TYPE_PCIE_BRIDGE:
+				ret = fn(tmp,
+					 PCI_DEVID(tmp->bus->number,
+						   tmp->devfn), data);
+				if (ret)
+					return ret;
+				continue;
+			}
+		} else {
+			ret = fn(tmp, PCI_DEVID(tmp->bus->number, tmp->devfn),
+				 data);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return ret;
+}
+
+/*
  * find the upstream PCIe-to-PCI bridge of a PCI device
  * if the device is PCIE, return NULL
  * if the device isn't connected to a PCIe bridge (that is its parent is a
diff --git a/include/linux/pci.h b/include/linux/pci.h
index aab57b4..14b074b 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1795,6 +1795,10 @@ static inline struct eeh_dev *pci_dev_to_eeh_dev(struct pci_dev *pdev)
 }
 #endif
 
+int pci_for_each_dma_alias(struct pci_dev *pdev,
+			   int (*fn)(struct pci_dev *pdev,
+				     u16 alias, void *data), void *data);
+
 /**
  * pci_find_upstream_pcie_bridge - find upstream PCIe-to-PCI bridge of a device
  * @pdev: the PCI device