[PATCH] arm64/pci: fix dma coherency inheritance for PCI devices

[Mark Salter]

The default dma_ops for devices on arm64 systems are noncoherent in
nature and rely upon special operations and bounce buffers to
perform a device DMA operation to/from memory. Some drivers rely
upon coherent operations involving suitably capable hardware. In
this case, a "dma-coherent" property will exist on the corresponding
Device Tree node for the bridge device, or one of its ancestors.
This patch adds support for applying a DMA coherent dma_ops for
PCI devices in the case of such a property.

Signed-off-by: Jon Masters <jcm at redhat.com>
[added search for device with of_node]
Signed-off-by: Mark Salter <msalter at redhat.com>
---
 arch/arm64/mm/dma-mapping.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 4164c5a..0e26bd7 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -23,10 +23,12 @@
 #include <linux/dma-mapping.h>
 #include <linux/dma-contiguous.h>
 #include <linux/of.h>
+#include <linux/of_address.h>
 #include <linux/platform_device.h>
 #include <linux/vmalloc.h>
 #include <linux/swiotlb.h>
 #include <linux/amba/bus.h>
+#include <linux/pci.h>
 
 #include <asm/cacheflush.h>
 
@@ -316,8 +318,18 @@ static int dma_bus_notifier(struct notifier_block *nb,
 	if (event != BUS_NOTIFY_ADD_DEVICE)
 		return NOTIFY_DONE;
 
-	if (of_property_read_bool(dev->of_node, "dma-coherent"))
-		set_dma_ops(dev, &coherent_swiotlb_dma_ops);
+	/*
+	 * Some devices won't have an of_node but a bus controller/bridge will.
+	 * Search up the device chain until we find an of_node to check.
+	 */
+	while (dev) {
+		if (dev->of_node) {
+			if (of_dma_is_coherent(dev->of_node))
+				set_dma_ops(_dev, &coherent_swiotlb_dma_ops);
+			break;
+		}
+		dev = dev->parent;
+	}
 
 	return NOTIFY_OK;
 }
@@ -330,6 +342,10 @@ static struct notifier_block amba_bus_nb = {
 	.notifier_call = dma_bus_notifier,
 };
 
+static struct notifier_block pci_bus_nb = {
+	.notifier_call = dma_bus_notifier,
+};
+
 extern int swiotlb_late_init_with_default_size(size_t default_size);
 
 static int __init swiotlb_late_init(void)
@@ -341,6 +357,7 @@ static int __init swiotlb_late_init(void)
 	 */
 	bus_register_notifier(&platform_bus_type, &platform_bus_nb);
 	bus_register_notifier(&amba_bustype, &amba_bus_nb);
+	bus_register_notifier(&pci_bus_type, &pci_bus_nb);
 
 	dma_ops = &noncoherent_swiotlb_dma_ops;
 
-- 
1.9.3