On Thursday 27 February 2014 16:17:49 Santosh Shilimkar wrote:

+
+/**
+ * of_dma_is_coherent - Check if device is coherent
+ * @np:        device node
+ *
+ * It returns true if "dma-coherent" property was found
+ * for this device in DT.
+ */
+bool of_dma_is_coherent(struct device_node *np)
+{
+       struct device_node *node = np;
+
+       while (node) {
+               if (of_property_read_bool(node, "dma-coherent")) {
+                       of_node_put(node);
+                       return true;
+               }
+               node = of_get_next_parent(node);
+       }
+       return false;
+}
+EXPORT_SYMBOL_GPL(of_dma_is_coherent);

This won't work on architectures that are always coherent and
did not need 'dma-coherent' properties before, such as IBM
Power servers.

That said, I think the property makes sense, and we already have
platforms using it (highbank is the one I'm aware of).

We probably need ways to override this function in both ways:
"always coherent" (powerpc, x86), and "never coherent" (keystone
without LPAE) from platform code, and it would be nice to put
either option into DT in a global location as well. We may have
to go through a few iterations of this patch to get the best
algorithm, but I think the interface is good at least.

	Arnd