[PATCH v2 6/6] ASoC: sun4i-i2s: Add support for loopback

[codekipper at gmail.com]

From: Marcus Cooper <codekipper at gmail.com>

The DAI has a loopback register which can be set and therefore routes
the transmit fifo to receive fifo. This is useful for testing the block
without the need for any external hardware.

Signed-off-by: Marcus Cooper <codekipper at gmail.com>
---
 Documentation/devicetree/bindings/sound/sun4i-i2s.txt |  3 +++
 sound/soc/sunxi/sun4i-i2s.c                           | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/devicetree/bindings/sound/sun4i-i2s.txt b/Documentation/devicetree/bindings/sound/sun4i-i2s.txt
index 3f966ac61b9e..325e3d4571f1 100644
--- a/Documentation/devicetree/bindings/sound/sun4i-i2s.txt
+++ b/Documentation/devicetree/bindings/sound/sun4i-i2s.txt
@@ -32,6 +32,9 @@ Optional properties:
 - allwinner,slot-width-override:if this property is present then the dai is
 				configured to extend the slot width to the
 				value specified. Min 8, Max 32.
+- loopback:	if this property is present then the dai is configured in
+		loopback mode where the output fifo is redirected to the input
+		fifo.
 
 - allwinner,playback-channels:  if this property is present then the number
 				of available channels is extended and the
diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c
index 7cf4dfe440de..a3c33814d33e 100644
--- a/sound/soc/sunxi/sun4i-i2s.c
+++ b/sound/soc/sunxi/sun4i-i2s.c
@@ -31,6 +31,7 @@
 #define SUN4I_I2S_CTRL_MODE_MASK		BIT(5)
 #define SUN4I_I2S_CTRL_MODE_SLAVE			(1 << 5)
 #define SUN4I_I2S_CTRL_MODE_MASTER			(0 << 5)
+#define SUN4I_I2S_CTRL_LOOP			BIT(3)
 #define SUN4I_I2S_CTRL_TX_EN			BIT(2)
 #define SUN4I_I2S_CTRL_RX_EN			BIT(1)
 #define SUN4I_I2S_CTRL_GL_EN			BIT(0)
@@ -195,6 +196,8 @@ struct sun4i_i2s {
 
 	const struct sun4i_i2s_quirks	*variant;
 
+	bool loopback;
+
 	unsigned int	slot_width;
 };
 
@@ -639,6 +642,11 @@ static void sun4i_i2s_start_capture(struct sun4i_i2s *i2s)
 	regmap_update_bits(i2s->regmap, SUN4I_I2S_DMA_INT_CTRL_REG,
 			   SUN4I_I2S_DMA_INT_CTRL_RX_DRQ_EN,
 			   SUN4I_I2S_DMA_INT_CTRL_RX_DRQ_EN);
+
+	/* Debugging without codec */
+	if (i2s->loopback)
+		regmap_update_bits(i2s->regmap, SUN4I_I2S_CTRL_REG,
+				   SUN4I_I2S_CTRL_LOOP, SUN4I_I2S_CTRL_LOOP);
 }
 
 static void sun4i_i2s_start_playback(struct sun4i_i2s *i2s)
@@ -1204,6 +1212,9 @@ static int sun4i_i2s_probe(struct platform_device *pdev)
 			soc_dai->playback.channels_max = val;
 	}
 
+	if (of_property_read_bool(pdev->dev.of_node, "loopback"))
+		i2s->loopback = true;
+
 	pm_runtime_enable(&pdev->dev);
 	if (!pm_runtime_enabled(&pdev->dev)) {
 		ret = sun4i_i2s_runtime_resume(&pdev->dev);
-- 
2.16.2