linux-kernel - [PATCH v2 1/2] ASoC: sophgo: cv1800b: document DAC overwrite handling

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Message-Id: <20260127-incremental-for-i2s-dvier-v2-1-5f66b841f63d@gmail.com>
Date: Tue, 27 Jan 2026 23:08:19 +0400
From: "Anton D. Stavinskii" <stavinsky@...il.com>
To: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Jaroslav Kysela <perex@...ex.cz>, 
 Takashi Iwai <tiwai@...e.com>, Paul Walmsley <pjw@...nel.org>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Chen Wang <unicorn_wang@...look.com>, 
 Inochi Amaoto <inochiama@...il.com>
Cc: linux-sound@...r.kernel.org, sophgo@...ts.linux.dev, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-riscv@...ts.infradead.org, 
 "Anton D. Stavinskii" <stavinsky@...il.com>
Subject: [PATCH v2 1/2] ASoC: sophgo: cv1800b: document DAC overwrite
 handling

Add comments to cv1800b_dac_mute() and its caller to explain how the
overwrite mechanism works and why we force it off before playback.

Signed-off-by: Anton D. Stavinskii <stavinsky@...il.com>
---
 sound/soc/sophgo/cv1800b-sound-dac.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sound/soc/sophgo/cv1800b-sound-dac.c b/sound/soc/sophgo/cv1800b-sound-dac.c
index ccf386174639..135322bcf6ad 100644
--- a/sound/soc/sophgo/cv1800b-sound-dac.c
+++ b/sound/soc/sophgo/cv1800b-sound-dac.c
@@ -57,6 +57,10 @@ static void cv1800b_dac_enable(struct cv1800b_priv *priv, bool enable)
 	writel(val, priv->regs + CV1800B_TXDAC_CTRL0);
 }

+/*
+ * Control the DAC overwrite bits. When enabled, the DAC outputs the fixed
+ * overwrite value instead of samples from the I2S input.
+ */
 static void cv1800b_dac_mute(struct cv1800b_priv *priv, bool enable)
 {
 	u32 val;
@@ -105,7 +109,7 @@ static int cv1800b_dac_hw_params(struct snd_pcm_substream *substream,
 		dev_err(priv->dev, "rate %u is not supported\n", rate);
 		return -EINVAL;
 	}
-
+	/* Clear DAC overwrite so playback uses I2S data. */
 	cv1800b_dac_mute(priv, false);
 	/* minimal decimation for 48kHz is 64*/
 	ret = cv1800b_dac_decimation(priv, DECIMATION_64);

-- 
2.43.0