[RFC PATCH 1/2] ASoC: loongson: Fix IISConfig0 update in hw_params for rev 1

[phucduc.bui@gmail.com]

From: bui duc phuc <phucduc.bui@gmail.com>

On revision 1 controllers, loongson_i2s_hw_params() reads LS_I2S_CFG
and ORs the new LR_LEN, BCLK_RATIO and RES_DEPTH values into it
without clearing the old ones.

The first stream after boot is configured correctly, but any later
stream with a different rate or sample width ends up with a mix of
old and new bits, so it may run with the wrong rate or sample width.

Use regmap_update_bits() to replace LR_LEN, BCLK_RATIO and the
RES_DEPTH field for the current direction while preserving the
other direction's RES_DEPTH field.

Fixes: d84881e06836 ("ASoC: Add support for Loongson I2S controller")
Signed-off-by: bui duc phuc <phucduc.bui@gmail.com>
---

Compile-tested only, I don't have the hardware. 
A Tested-by from someone with a 2K0300, 2K2000 board would be appreciated.

The field layout follows the Loongson-2K0300 user manual (IISConfig0) [1].
 
Not sure whether concurrent playback and capture is supported on this controller. 
If it is, note that LR_LEN and BCLK_RATIO are shared, so the stream started later 
would overwrite them when the sample width or channel count differs. 
I can follow up with symmetric_channels and symmetric_sample_bits if that is 
the right fix.

[1] https://github.com/loongson-community/docs/blob/master/2K0300/2025060909243029508.%E9%BE%99%E8%8A%AF2K0300%E5%A4%84%E7%90%86%E5%99%A8%E7%94%A8%E6%88%B7%E6%89%8B%E5%86%8C_V1.01.pdf

 sound/soc/loongson/loongson_i2s.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/sound/soc/loongson/loongson_i2s.c b/sound/soc/loongson/loongson_i2s.c
index da0d029c028a..109cb61c6ddf 100644
--- a/sound/soc/loongson/loongson_i2s.c
+++ b/sound/soc/loongson/loongson_i2s.c
@@ -69,6 +69,7 @@ static int loongson_i2s_hw_params(struct snd_pcm_substream *substream,
 	u32 fs = params_rate(params);
 	u32 bclk_ratio, mclk_ratio;
 	u32 mclk_ratio_frac;
+	u32 mask;
 	u32 val = 0;
 
 	switch (i2s->rev_id) {
@@ -92,14 +93,19 @@ static int loongson_i2s_hw_params(struct snd_pcm_substream *substream,
 		mclk_ratio_frac = DIV_ROUND_CLOSEST_ULL(((u64)clk_rate << 16),
 						    sysclk) - (mclk_ratio << 16);
 
-		regmap_read(i2s->regmap, LS_I2S_CFG, &val);
-		val |= (bits << 24);
-		val |= (bclk_ratio << 8);
-		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		/* Shared fields: LR_LEN [31:24], BCLK_RATIO [15:8] */
+		mask = GENMASK(31, 24) | GENMASK(15, 8);
+		val = (bits << 24) | (bclk_ratio << 8);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+			/* TX_RES_DEPTH */
+			mask |= GENMASK(23, 16);
 			val |= (bits << 16);
-		else
+		} else {
+			/* RX_RES_DEPTH */
+			mask |= GENMASK(7, 0);
 			val |= bits;
-		regmap_write(i2s->regmap, LS_I2S_CFG, val);
+		}
+		regmap_update_bits(i2s->regmap, LS_I2S_CFG, mask, val);
 
 		val = (mclk_ratio_frac << 16) | mclk_ratio;
 		regmap_write(i2s->regmap, LS_I2S_CFG1, val);
-- 
2.43.0