[alsa-devel] [PATCH 2/4] ALSA: hda: Make sure DMA is started by reading back the RUN bit

[Sriram Periyasamy]

From: Pardha Saradhi K <pardha.saradhi.kesapragada at intel.com>

As per HW recommendation, after setting the RUN bit,
software must read a 1 from the RUN bit, before modifying
related control registers/re-starting the DMA engine.

Signed-off-by: Pardha Saradhi K <pardha.saradhi.kesapragada at intel.com>
Signed-off-by: Sriram Periyasamy <sriramx.periyasamy at intel.com>
---
 sound/hda/hdac_stream.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/sound/hda/hdac_stream.c b/sound/hda/hdac_stream.c
index 2000ea6f48fa..33c8ced528f6 100644
--- a/sound/hda/hdac_stream.c
+++ b/sound/hda/hdac_stream.c
@@ -48,6 +48,8 @@ EXPORT_SYMBOL_GPL(snd_hdac_stream_init);
 void snd_hdac_stream_start(struct hdac_stream *azx_dev, bool fresh_start)
 {
 	struct hdac_bus *bus = azx_dev->bus;
+	int timeout = 300;
+	unsigned char val;
 
 	trace_snd_hdac_stream_start(bus, azx_dev);
 
@@ -60,6 +62,20 @@ void snd_hdac_stream_start(struct hdac_stream *azx_dev, bool fresh_start)
 	/* set DMA start and interrupt mask */
 	snd_hdac_stream_updateb(azx_dev, SD_CTL,
 				0, SD_CTL_DMA_START | SD_INT_MASK);
+
+	do {
+		udelay(3);
+		val = snd_hdac_stream_readb(azx_dev, SD_CTL) & SD_CTL_DMA_START;
+		if (val)
+			break;
+	} while (--timeout);
+
+	if (!timeout) {
+		azx_dev->running = false;
+		dev_err(azx_dev->bus->dev, "unable to start the stream\n");
+		return;
+	}
+
 	azx_dev->running = true;
 }
 EXPORT_SYMBOL_GPL(snd_hdac_stream_start);
-- 
2.7.4