of/pci: Add of_pci_dma_configure() to update DMA configuration

Add of_pci_dma_configure() to allow updating the DMA configuration of the
PCI device using the configuration from DT of the parent of the root bridge
device. Use the newly added APIs pci_get/put_host_bridge_device() for
implementing this.

[bhelgaas: fold in fix for host bridges with no parent OF device]
Tested-by: Suravee Suthikulpanit <[e-mail]> (AMD Seattle)
Signed-off-by: Murali Karicheri <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Catalin Marinas <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
CC: Joerg Roedel <[e-mail]>
CC: Grant Likely <[e-mail]>
CC: Russell King <[e-mail]>
CC: Arnd Bergmann <[e-mail]>

drivers/of/of_pci.c

···
 #include <linux/export.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_device.h>
 #include <linux/of_pci.h>
 #include <linux/slab.h>
 
···
 	return domain;
 }
 EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
+
+/**
+ * of_pci_dma_configure - Setup DMA configuration
+ * @dev: ptr to pci_dev struct of the PCI device
+ *
+ * Function to update PCI devices's DMA configuration using the same
+ * info from the OF node of host bridge's parent (if any).
+ */
+void of_pci_dma_configure(struct pci_dev *pci_dev)
+{
+	struct device *dev = &pci_dev->dev;
+	struct device *bridge = pci_get_host_bridge_device(pci_dev);
+
+	if (!bridge->parent)
+		return;
+
+	of_dma_configure(dev, bridge->parent->of_node);
+	pci_put_host_bridge_device(bridge);
+}
+EXPORT_SYMBOL_GPL(of_pci_dma_configure);
 
 #if defined(CONFIG_OF_ADDRESS)
 /**

include/linux/of_pci.h

···
 int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin);
 int of_pci_parse_bus_range(struct device_node *node, struct resource *res);
 int of_get_pci_domain_nr(struct device_node *node);
+void of_pci_dma_configure(struct pci_dev *pci_dev);
 #else
 static inline int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
 {
···
 {
 	return -1;
 }
+
+static inline void of_pci_dma_configure(struct pci_dev *pci_dev) { }
 #endif
 
 #if defined(CONFIG_OF_ADDRESS)