[RFC 2/3] dmaengine: of_dma: Function to look up the DMA domain of a client

[Peter Ujfalusi <peter.ujfalusi@xxxxxx>]

Find the DMA domain controller of the client device by iterating up in
device tree looking for the closest 'dma-domain-controller' property.

If the client's node is not provided then check the DT root for the
controller.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
---
 drivers/dma/of-dma.c   | 42 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/of_dma.h |  7 +++++++
 2 files changed, 49 insertions(+)

diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
index c2d779daa4b5..04b5795cd76b 100644
--- a/drivers/dma/of-dma.c
+++ b/drivers/dma/of-dma.c
@@ -18,6 +18,48 @@
 static LIST_HEAD(of_dma_list);
 static DEFINE_MUTEX(of_dma_lock);
 
+/**
+ * of_find_dma_domain - Get the domain DMA controller
+ * @np:		device node of the client device
+ *
+ * Look up the DMA controller of the domain the client device is part of.
+ * Finds the dma-domain controller the client device belongs to. It is used when
+ * requesting non slave channels (like channel for memcpy) to make sure that the
+ * channel can be request from a DMA controller which can service the given
+ * domain best.
+ *
+ * Returns the device_node pointer of the DMA controller or succes or NULL on
+ * error.
+ */
+struct device_node *of_find_dma_domain(struct device_node *np)
+{
+	struct device_node *dma_domain = NULL;
+	phandle dma_phandle;
+
+	/*
+	 * If no device_node is provided look at the root level for system
+	 * default DMA controller for modules.
+	 */
+	if (!np)
+		np = of_root;
+
+	if (!np || !of_node_get(np))
+		return NULL;
+
+	do {
+		if (of_property_read_u32(np, "dma-domain-controller",
+					 &dma_phandle))
+			np = of_get_next_parent(np);
+		else {
+			dma_domain = of_find_node_by_phandle(dma_phandle);
+			of_node_put(np);
+		}
+	} while (!dma_domain && np);
+
+	return dma_domain;
+}
+EXPORT_SYMBOL_GPL(of_find_dma_domain);
+
 /**
  * of_dma_find_controller - Get a DMA controller in DT DMA helpers list
  * @dma_spec:	pointer to DMA specifier as found in the device tree
diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
index fd706cdf255c..6eab0a8d3335 100644
--- a/include/linux/of_dma.h
+++ b/include/linux/of_dma.h
@@ -32,6 +32,8 @@ struct of_dma_filter_info {
 };
 
 #ifdef CONFIG_DMA_OF
+extern struct device_node *of_find_dma_domain(struct device_node *np);
+
 extern int of_dma_controller_register(struct device_node *np,
 		struct dma_chan *(*of_dma_xlate)
 		(struct of_phandle_args *, struct of_dma *),
@@ -52,6 +54,11 @@ extern struct dma_chan *of_dma_xlate_by_chan_id(struct of_phandle_args *dma_spec
 		struct of_dma *ofdma);
 
 #else
+static inline struct device_node *of_find_dma_domain(struct device_node *np)
+{
+	return NULL;
+}
+
 static inline int of_dma_controller_register(struct device_node *np,
 		struct dma_chan *(*of_dma_xlate)
 		(struct of_phandle_args *, struct of_dma *),
-- 
Peter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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