iommu/of: Handle iommu-map property for PCI

Now that we have a way to pick up the RID translation and target IOMMU,
hook up of_iommu_configure() to bring PCI devices into the of_xlate
mechanism and allow them IOMMU-backed DMA ops without the need for
driver-specific handling.

Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/iommu/of_iommu.c

@@ -22,6 +22,7 @@
 #include <linux/limits.h>
 #include <linux/of.h>
 #include <linux/of_iommu.h>
+#include <linux/of_pci.h>
 #include <linux/slab.h>
 
 static const struct of_device_id __iommu_of_table_sentinel
@@ -134,6 +135,45 @@ const struct iommu_ops *of_iommu_get_ops(struct device_node *np)
 	return ops;
 }
 
+static int __get_pci_rid(struct pci_dev *pdev, u16 alias, void *data)
+{
+	struct of_phandle_args *iommu_spec = data;
+
+	iommu_spec->args[0] = alias;
+	return iommu_spec->np == pdev->bus->dev.of_node;
+}
+
+static const struct iommu_ops
+*of_pci_iommu_configure(struct pci_dev *pdev, struct device_node *bridge_np)
+{
+	const struct iommu_ops *ops;
+	struct of_phandle_args iommu_spec;
+
+	/*
+	 * Start by tracing the RID alias down the PCI topology as
+	 * far as the host bridge whose OF node we have...
+	 * (we're not even attempting to handle multi-alias devices yet)
+	 */
+	iommu_spec.args_count = 1;
+	iommu_spec.np = bridge_np;
+	pci_for_each_dma_alias(pdev, __get_pci_rid, &iommu_spec);
+	/*
+	 * ...then find out what that becomes once it escapes the PCI
+	 * bus into the system beyond, and which IOMMU it ends up at.
+	 */
+	iommu_spec.np = NULL;
+	if (of_pci_map_rid(bridge_np, iommu_spec.args[0], "iommu-map",
+			   "iommu-map-mask", &iommu_spec.np, iommu_spec.args))
+		return NULL;
+
+	ops = of_iommu_get_ops(iommu_spec.np);
+	if (!ops || !ops->of_xlate || ops->of_xlate(&pdev->dev, &iommu_spec))
+		ops = NULL;
+
+	of_node_put(iommu_spec.np);
+	return ops;
+}
+
 const struct iommu_ops *of_iommu_configure(struct device *dev,
 					   struct device_node *master_np)
 {
@@ -142,12 +182,8 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
 	const struct iommu_ops *ops = NULL;
 	int idx = 0;
 
-	/*
-	 * We can't do much for PCI devices without knowing how
-	 * device IDs are wired up from the PCI bus to the IOMMU.
-	 */
 	if (dev_is_pci(dev))
-		return NULL;
+		return of_pci_iommu_configure(to_pci_dev(dev), master_np);
 
 	/*
 	 * We don't currently walk up the tree looking for a parent IOMMU.