linux-kernel - [PATCH v2] DMA: add help function to check whether dma controller registered

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Date:	Thu, 22 Aug 2013 14:43:00 +0800
From:	Richard Zhao <rizhao@...dia.com>
To:	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	<vinod.koul@...el.com>, <djbw@...com>, <swarren@...dotorg.org>,
	<grant.likely@...aro.org>, <rob.herring@...xeda.com>,
	<devicetree@...r.kernel.org>, Richard Zhao <rizhao@...dia.com>
Subject: [PATCH v2] DMA: add help function to check whether dma controller registered

DMA client device driver usually needs to know at probe time whether
dma controller has been registered to deffer probe. So add a help
function of_dma_check_controller.

DMA request channel functions can also used to check it, but they
are usually called at open() time.

Signed-off-by: Richard Zhao <rizhao@...dia.com>
---
 drivers/dma/of-dma.c   | 39 +++++++++++++++++++++++++++++++++++++++
 include/linux/of_dma.h |  6 ++++++
 2 files changed, 45 insertions(+)

diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
index 8cd5f3f..0063ddf 100644
--- a/drivers/dma/of-dma.c
+++ b/drivers/dma/of-dma.c
@@ -189,6 +189,45 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
 }
 
 /**
+ * of_dma_check_controller - Check whether dma controller registered
+ * @dev:	pointer to client device structure
+ * @name:	slave channel name
+ */
+int of_dma_check_controller(struct device *dev, const char *name)
+{
+	struct device_node *np = dev->of_node;
+	struct of_phandle_args dma_spec;
+	struct of_dma *ofdma = NULL;
+	int count, i, ret = 0;
+
+	if (!np || !name)
+		return -EINVAL;
+
+	count = of_property_count_strings(np, "dma-names");
+	if (count < 0) {
+		dev_err(dev, "dma-names property missing or empty\n");
+		return -EINVAL;
+	}
+
+	for (i = 0; i < count; i++) {
+		ret = of_dma_match_channel(np, name, i, &dma_spec);
+		if (ret)
+			continue;
+
+		mutex_lock(&of_dma_lock);
+		ofdma = of_dma_find_controller(&dma_spec);
+		mutex_unlock(&of_dma_lock);
+		of_node_put(dma_spec.np);
+		if (!ofdma)
+			ret = -EPROBE_DEFER;
+		break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(of_dma_check_controller);
+
+/**
  * of_dma_simple_xlate - Simple DMA engine translation function
  * @dma_spec:	pointer to DMA specifier as found in the device tree
  * @of_dma:	pointer to DMA controller data
diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
index ae36298..bc7195f 100644
--- a/include/linux/of_dma.h
+++ b/include/linux/of_dma.h
@@ -39,6 +39,7 @@ extern int of_dma_controller_register(struct device_node *np,
 extern void of_dma_controller_free(struct device_node *np);
 extern struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
 						     const char *name);
+extern int of_dma_check_controller(struct device *dev, const char *name);
 extern struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec,
 		struct of_dma *ofdma);
 #else
@@ -60,6 +61,11 @@ static inline struct dma_chan *of_dma_request_slave_channel(struct device_node *
 	return NULL;
 }
 
+static inline int of_dma_check_controller(struct device *dev, const char *name)
+{
+	return 0;
+}
+
 static inline struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec,
 		struct of_dma *ofdma)
 {
-- 
1.8.1.5

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