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

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Date:   Mon, 20 Apr 2020 14:56:31 +0200
From:   Clément Péron <peron.clem@...il.com>
To:     Maxime Ripard <maxime@...no.tech>
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>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Marcus Cooper <codekipper@...il.com>
Subject: Re: [PATCH v2 4/7] ASoC: sun4i-i2s: Set sign extend sample

Hi Maxime,

On Mon, 20 Apr 2020 at 14:44, Maxime Ripard <maxime@...no.tech> wrote:
>
> 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?

To keep coherency between all set_soc_format(), and also avoid this
kind of issue for future generation.
As this doesn't cost much after all, and it avoid to rely on default,
but what do you think ?

Clement

>
> Maxime