of: Fix "dma-ranges" handling for bus controllers

Commit 951d48855d86 ("of: Make of_dma_get_range() work on bus nodes")
relaxed the handling of "dma-ranges" for any leaf node on the assumption
that it would still represent a usage error for the property to be
present on a non-bus leaf node. However there turns out to be a fiddly
case where a bus also represents a DMA-capable device in its own right,
such as a PCIe root complex with an integrated DMA engine on its
platform side. In such cases, "dma-ranges" translation is entirely valid
for devices discovered behind the bus, but should not be erroneously
applied to the bus controller device itself which operates in its
parent's address space. Fix this by restoring the previous behaviour for
the specific case where a device is configured via its own OF node,
since it is logical to assume that a device should never represent its
own parent bus.

Reported-by: Serge Semin <[e-mail]>
Signed-off-by: Robin Murphy <[e-mail]>
Link: https://lore.kernel.org/r/112e[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

drivers/of/address.c

···
 }
 EXPORT_SYMBOL(of_translate_address);
 
-static struct device_node *__of_get_dma_parent(const struct device_node *np)
+#ifdef CONFIG_HAS_DMA
+struct device_node *__of_get_dma_parent(const struct device_node *np)
 {
 	struct of_phandle_args args;
 	int ret, index;
···
 
 	return of_node_get(args.np);
 }
+#endif
 
 static struct device_node *of_get_next_dma_parent(struct device_node *np)
 {

drivers/of/device.c

···
 {
 	const struct iommu_ops *iommu;
 	const struct bus_dma_region *map = NULL;
+	struct device_node *bus_np;
 	u64 dma_start = 0;
 	u64 mask, end, size = 0;
 	bool coherent;
 	int ret;
 
-	ret = of_dma_get_range(np, &map);
+	if (np == dev->of_node)
+		bus_np = __of_get_dma_parent(np);
+	else
+		bus_np = of_node_get(np);
+
+	ret = of_dma_get_range(bus_np, &map);
+	of_node_put(bus_np);
 	if (ret < 0) {
 		/*
 		 * For legacy reasons, we have to assume some devices need

drivers/of/of_private.h

···
 #if defined(CONFIG_OF_ADDRESS) && defined(CONFIG_HAS_DMA)
 int of_dma_get_range(struct device_node *np,
 		const struct bus_dma_region **map);
+struct device_node *__of_get_dma_parent(const struct device_node *np);
 #else
 static inline int of_dma_get_range(struct device_node *np,
 		const struct bus_dma_region **map)
 {
 	return -ENODEV;
+}
+static inline struct device_node *__of_get_dma_parent(const struct device_node *np)
+{
+	return of_get_parent(np);
 }
 #endif