[PATCH] ASoC: meson: axg-frddr: set fifo depth according to the period

[Jerome Brunet]

When the period is small, using all the FRDDR fifo depth increases the
latency of the playback because the following device won't start pulling
data until the fifo reaches the depth set. We can adjust this depth so trim
it down for small periods.

Signed-off-by: Jerome Brunet <jbrunet at baylibre.com>
---
 sound/soc/meson/axg-frddr.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/sound/soc/meson/axg-frddr.c b/sound/soc/meson/axg-frddr.c
index c3ae8ac30745..8ed114de0bdf 100644
--- a/sound/soc/meson/axg-frddr.c
+++ b/sound/soc/meson/axg-frddr.c
@@ -11,6 +11,7 @@
 #include <linux/regmap.h>
 #include <linux/module.h>
 #include <linux/of_platform.h>
+#include <sound/pcm_params.h>
 #include <sound/soc.h>
 #include <sound/soc-dai.h>
 
@@ -46,11 +47,28 @@ static int g12a_frddr_dai_prepare(struct snd_pcm_substream *substream,
 	return 0;
 }
 
+static int axg_frddr_dai_hw_params(struct snd_pcm_substream *substream,
+				   struct snd_pcm_hw_params *params,
+				   struct snd_soc_dai *dai)
+{
+	struct axg_fifo *fifo = snd_soc_dai_get_drvdata(dai);
+	unsigned int period, depth, val;
+
+	period = params_period_bytes(params);
+
+	/* Trim the FIFO depth if the period is small to improve latency */
+	depth = min(period, fifo->depth);
+	val = (depth / AXG_FIFO_BURST) - 1;
+	regmap_update_bits(fifo->map, FIFO_CTRL1, CTRL1_FRDDR_DEPTH_MASK,
+			   CTRL1_FRDDR_DEPTH(val));
+
+	return 0;
+}
+
 static int axg_frddr_dai_startup(struct snd_pcm_substream *substream,
 				 struct snd_soc_dai *dai)
 {
 	struct axg_fifo *fifo = snd_soc_dai_get_drvdata(dai);
-	unsigned int val;
 	int ret;
 
 	/* Enable pclk to access registers and clock the fifo ip */
@@ -61,11 +79,6 @@ static int axg_frddr_dai_startup(struct snd_pcm_substream *substream,
 	/* Apply single buffer mode to the interface */
 	regmap_update_bits(fifo->map, FIFO_CTRL0, CTRL0_FRDDR_PP_MODE, 0);
 
-	/* Use all fifo depth */
-	val = (fifo->depth / AXG_FIFO_BURST) - 1;
-	regmap_update_bits(fifo->map, FIFO_CTRL1, CTRL1_FRDDR_DEPTH_MASK,
-			   CTRL1_FRDDR_DEPTH(val));
-
 	return 0;
 }
 
@@ -84,6 +97,7 @@ static int axg_frddr_pcm_new(struct snd_soc_pcm_runtime *rtd,
 }
 
 static const struct snd_soc_dai_ops axg_frddr_ops = {
+	.hw_params	= axg_frddr_dai_hw_params,
 	.startup	= axg_frddr_dai_startup,
 	.shutdown	= axg_frddr_dai_shutdown,
 };
-- 
2.30.2