[PATCH 1/2] ASoC: tas2562: fix DVC coefficient write order

[Haidar Lee via B4 Relay]

From: Haidar Lee <haidar.lee@xxxxxxxxxxxxxx>

The TAS2562 applies the 32-bit digital volume coefficient to the
playback path when the last byte, DVC_CFG4 (book 0 page 2 reg 0x0F), is
written. tas2562_volume_control_put() wrote DVC_CFG4 first and DVC_CFG1
(the MSB) last, so every volume change latched a value made of the
previous coefficient's upper three bytes combined with the new LSB; the
remaining bytes only took effect on the next volume change.

In practice the control was unusable: the first setting after power-on
always played at roughly 0 dB no matter what value was requested (the
chip's default upper bytes were still latched), and most subsequent
changes muted the output entirely or produced a distorted, over-unity
gain.

Verified on a TAS2562 (ADLINK OSM-520 / MT8189 board) by tracing the
I2C writes with ftrace and by writing the same coefficients manually in
both byte orders: written MSB-first the register block behaves exactly
as the driver expects, LSB-first reproduces the broken behaviour.

Write the bytes MSB first with DVC_CFG4 last so the complete new
coefficient is latched atomically.

Fixes: bf726b1c86f2 ("ASoC: tas2562: Add support for digital volume control")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Haidar Lee <haidar.lee@xxxxxxxxxxxxxx>
---
 sound/soc/codecs/tas2562.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/sound/soc/codecs/tas2562.c b/sound/soc/codecs/tas2562.c
index e1d62f30418a..ec32ef0afd7e 100644
--- a/sound/soc/codecs/tas2562.c
+++ b/sound/soc/codecs/tas2562.c
@@ -475,20 +475,27 @@ static int tas2562_volume_control_put(struct snd_kcontrol *kcontrol,
 	u32 reg_val;
 
 	reg_val = float_vol_db_lookup[ucontrol->value.integer.value[0]/2];
-	ret = snd_soc_component_write(component, TAS2562_DVC_CFG4,
-				      (reg_val & 0xff));
-	if (ret)
-		return ret;
-	ret = snd_soc_component_write(component, TAS2562_DVC_CFG3,
-				      ((reg_val >> 8) & 0xff));
+	/*
+	 * The device applies the 32-bit coefficient to the playback path on
+	 * the write to DVC_CFG4 (the LSB, book 0 page 2 reg 0x0F), so the
+	 * bytes must be written MSB first and DVC_CFG4 last. Writing CFG4
+	 * first latches a mix of the previous coefficient's upper bytes and
+	 * the new LSB instead of the requested value.
+	 */
+	ret = snd_soc_component_write(component, TAS2562_DVC_CFG1,
+				      ((reg_val >> 24) & 0xff));
 	if (ret)
 		return ret;
 	ret = snd_soc_component_write(component, TAS2562_DVC_CFG2,
 				      ((reg_val >> 16) & 0xff));
 	if (ret)
 		return ret;
-	ret = snd_soc_component_write(component, TAS2562_DVC_CFG1,
-				      ((reg_val >> 24) & 0xff));
+	ret = snd_soc_component_write(component, TAS2562_DVC_CFG3,
+				      ((reg_val >> 8) & 0xff));
+	if (ret)
+		return ret;
+	ret = snd_soc_component_write(component, TAS2562_DVC_CFG4,
+				      (reg_val & 0xff));
 	if (ret)
 		return ret;
 

-- 
2.34.1