ASoC: sun4i-i2s: Set sign extend sample

On the newer SoCs such as the H3 and A64 this is set by default
to transfer a 0 after each sample in each slot. However the A10
and A20 SoCs that this driver was developed on had a default
setting where it padded the audio gain with zeros.

This isn't a problem while we have only support for 16bit audio
but with larger sample resolution rates in the pipeline then SEXT
bits should be cleared so that they also pad at the LSB. Without
this the audio gets distorted.

Set sign extend sample for all the sunxi generations even if they
are not affected. This will keep consistency and avoid relying on
default.
Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Link: https://lore.kernel.org/r/20201030144648.397824-6-peron.clem@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sunxi/sun4i-i2s.c

@@ -48,6 +48,9 @@
 #define SUN4I_I2S_FMT0_FMT_I2S				(0 << 0)
 
 #define SUN4I_I2S_FMT1_REG		0x08
+#define SUN4I_I2S_FMT1_REG_SEXT_MASK		BIT(8)
+#define SUN4I_I2S_FMT1_REG_SEXT(sext)			((sext) << 8)
+
 #define SUN4I_I2S_FIFO_TX_REG		0x0c
 #define SUN4I_I2S_FIFO_RX_REG		0x10
 
@@ -105,6 +108,9 @@
 #define SUN8I_I2S_FMT0_BCLK_POLARITY_INVERTED		(1 << 7)
 #define SUN8I_I2S_FMT0_BCLK_POLARITY_NORMAL		(0 << 7)
 
+#define SUN8I_I2S_FMT1_REG_SEXT_MASK		GENMASK(5, 4)
+#define SUN8I_I2S_FMT1_REG_SEXT(sext)			((sext) << 4)
+
 #define SUN8I_I2S_INT_STA_REG		0x0c
 #define SUN8I_I2S_FIFO_TX_REG		0x20
 
@@ -686,6 +692,7 @@ static int sun4i_i2s_set_soc_fmt(const struct sun4i_i2s *i2s,
 	}
 	regmap_update_bits(i2s->regmap, SUN4I_I2S_CTRL_REG,
 			   SUN4I_I2S_CTRL_MODE_MASK, val);
+
 	return 0;
 }
 
@@ -788,6 +795,11 @@ static int sun8i_i2s_set_soc_fmt(const struct sun4i_i2s *i2s,
 			   SUN8I_I2S_CTRL_BCLK_OUT | SUN8I_I2S_CTRL_LRCK_OUT,
 			   val);
 
+	/* Set sign extension to pad out LSB with 0 */
+	regmap_update_bits(i2s->regmap, SUN4I_I2S_FMT1_REG,
+			   SUN8I_I2S_FMT1_REG_SEXT_MASK,
+			   SUN8I_I2S_FMT1_REG_SEXT(0));
+
 	return 0;
 }
 
@@ -890,6 +902,11 @@ static int sun50i_h6_i2s_set_soc_fmt(const struct sun4i_i2s *i2s,
 			   SUN8I_I2S_CTRL_BCLK_OUT | SUN8I_I2S_CTRL_LRCK_OUT,
 			   val);
 
+	/* Set sign extension to pad out LSB with 0 */
+	regmap_update_bits(i2s->regmap, SUN4I_I2S_FMT1_REG,
+			   SUN8I_I2S_FMT1_REG_SEXT_MASK,
+			   SUN8I_I2S_FMT1_REG_SEXT(0));
+
 	return 0;
 }