linux-kernel - Re: [PATCH v2 4/7] ASoC: sun4i-i2s: Set sign extend sample

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Message-ID: <20200420124452.5vaoyw73n76jwmey@gilmour.lan>
Date:   Mon, 20 Apr 2020 14:44:52 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Clément Péron <peron.clem@...il.com>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Marcus Cooper <codekipper@...il.com>
Subject: Re: [PATCH v2 4/7] ASoC: sun4i-i2s: Set sign extend sample

On Sun, Apr 19, 2020 at 12:44:32AM +0200, Clément Péron wrote:
> From: Marcus Cooper <codekipper@...il.com>
> 
> 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 whilst 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.
> 
> Signed-off-by: Marcus Cooper <codekipper@...il.com>
> Signed-off-by: Clément Péron <peron.clem@...il.com>
> ---
>  sound/soc/sunxi/sun4i-i2s.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c
> index a23c9f2a3f8c..618bbc5156f1 100644
> --- a/sound/soc/sunxi/sun4i-i2s.c
> +++ b/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
>  
> @@ -663,6 +669,12 @@ 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);
> +
> +	/* Set sign extension to pad out LSB with 0 */
> +	regmap_update_bits(i2s->regmap, SUN4I_I2S_FMT1_REG,
> +			   SUN4I_I2S_FMT1_REG_SEXT_MASK,
> +			   SUN4I_I2S_FMT1_REG_SEXT(0));
> +
>  	return 0;
>  }
>  
> @@ -765,6 +777,11 @@ 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;
>  }
>  
> @@ -867,6 +884,11 @@ static int sun50i_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));
> +

If this is an issue only on the A10 / A20, why are you setting it up on the
other generations too?

Maxime

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