Re: [linux-sunxi] [PATCH 2/3] ASoC: sun4i-i2s: Do not divide clocks when slave

[Chen-Yu Tsai <wens@csie.org>]

On Wed, Jan 24, 2018 at 10:11 PM,  <codekipper@gmail.com> wrote:
> From: Marcus Cooper <codekipper@gmail.com>

Subject is slightly hard to read.

ASoC: sun4i-i2s: Do not divide clocks when acting as slave

would be easier to understand.

>
> There is no need to set the clock and calculate the division of
> the audio pll for the bclk and sync signals when they are not
> required.
>
> Signed-off-by: Marcus Cooper <codekipper@gmail.com>
> ---
>  sound/soc/sunxi/sun4i-i2s.c | 116 ++++++++++++++++++++++++--------------------
>  1 file changed, 64 insertions(+), 52 deletions(-)
>
> diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c
> index d7a9141514cf..626679057d0f 100644
> --- a/sound/soc/sunxi/sun4i-i2s.c
> +++ b/sound/soc/sunxi/sun4i-i2s.c
> @@ -195,6 +195,8 @@ struct sun4i_i2s {
>
>         const struct sun4i_i2s_quirks   *variant;
>
> +       bool bit_clk_master;
> +
>         unsigned int    tdm_slots;
>         unsigned int    slot_width;
>  };
> @@ -282,67 +284,73 @@ static int sun4i_i2s_set_clk_rate(struct snd_soc_dai *dai,
>         int bclk_div, mclk_div;
>         int ret;
>
> -       switch (rate) {
> -       case 176400:
> -       case 88200:
> -       case 44100:
> -       case 22050:
> -       case 11025:
> -               clk_rate = 22579200;
> -               break;
> +       if (i2s->bit_clk_master) {
> +               switch (rate) {
> +               case 176400:
> +               case 88200:
> +               case 44100:
> +               case 22050:
> +               case 11025:
> +                       clk_rate = 22579200;
> +                       break;
>
> -       case 192000:
> -       case 128000:
> -       case 96000:
> -       case 64000:
> -       case 48000:
> -       case 32000:
> -       case 24000:
> -       case 16000:
> -       case 12000:
> -       case 8000:
> -               clk_rate = 24576000;
> -               break;
> +               case 192000:
> +               case 128000:
> +               case 96000:
> +               case 64000:
> +               case 48000:
> +               case 32000:
> +               case 24000:
> +               case 16000:
> +               case 12000:
> +               case 8000:
> +                       clk_rate = 24576000;
> +                       break;
>
> -       default:
> -               dev_err(dai->dev, "Unsupported sample rate: %u\n", rate);
> -               return -EINVAL;
> -       }
> +               default:
> +                       dev_err(dai->dev, "Unsupported sample rate: %u\n", rate);
> +                       return -EINVAL;
> +               }
>
> -       ret = clk_set_rate(i2s->mod_clk, clk_rate);
> -       if (ret)
> -               return ret;
> +               ret = clk_set_rate(i2s->mod_clk, clk_rate);
> +               if (ret) {
> +                       dev_err(dai->dev, "Unable to set clock\n");
> +                       return ret;
> +               }
>
> -       oversample_rate = i2s->mclk_freq / rate;
> -       if (!sun4i_i2s_oversample_is_valid(oversample_rate)) {
> -               dev_err(dai->dev, "Unsupported oversample rate: %d\n",
> -                       oversample_rate);
> -               return -EINVAL;
> -       }
> +               oversample_rate = i2s->mclk_freq / rate;
> +               if (!sun4i_i2s_oversample_is_valid(oversample_rate)) {
> +                       dev_err(dai->dev, "Unsupported oversample rate: %d\n",
> +                               oversample_rate);
> +                       return -EINVAL;
> +               }
>
> -       bclk_div = sun4i_i2s_get_bclk_div(i2s, oversample_rate,
> -                                         word_size);
> -       if (bclk_div < 0) {
> -               dev_err(dai->dev, "Unsupported BCLK divider: %d\n", bclk_div);
> -               return -EINVAL;
> -       }
> +               bclk_div = sun4i_i2s_get_bclk_div(i2s, oversample_rate,
> +                                                 word_size);
> +               if (bclk_div < 0) {
> +                       dev_err(dai->dev, "Unsupported BCLK divider: %d\n",
> +                               bclk_div);
> +                       return -EINVAL;
> +               }
>
> -       mclk_div = sun4i_i2s_get_mclk_div(i2s, oversample_rate,
> -                                         clk_rate, rate);
> -       if (mclk_div < 0) {
> -               dev_err(dai->dev, "Unsupported MCLK divider: %d\n", mclk_div);
> -               return -EINVAL;
> -       }
> +               mclk_div = sun4i_i2s_get_mclk_div(i2s, oversample_rate,
> +                                                 clk_rate, rate);
> +               if (mclk_div < 0) {
> +                       dev_err(dai->dev, "Unsupported MCLK divider: %d\n",
> +                               mclk_div);
> +                       return -EINVAL;
> +               }
>
> -       /* Adjust the clock division values if needed */
> -       bclk_div += i2s->variant->bclk_offset;
> -       mclk_div += i2s->variant->mclk_offset;
> +               /* Adjust the clock division values if needed */
> +               bclk_div += i2s->variant->bclk_offset;
> +               mclk_div += i2s->variant->mclk_offset;
>
> -       regmap_write(i2s->regmap, SUN4I_I2S_CLK_DIV_REG,
> -                    SUN4I_I2S_CLK_DIV_BCLK(bclk_div) |
> -                    SUN4I_I2S_CLK_DIV_MCLK(mclk_div));
> +               regmap_write(i2s->regmap, SUN4I_I2S_CLK_DIV_REG,
> +                            SUN4I_I2S_CLK_DIV_BCLK(bclk_div) |
> +                            SUN4I_I2S_CLK_DIV_MCLK(mclk_div));
>
> -       regmap_field_write(i2s->field_clkdiv_mclk_en, 1);
> +               regmap_field_write(i2s->field_clkdiv_mclk_en, 1);
> +       }

The changed block is so long that it seems better to split it out
into a helper function that doesn't get called when the controller
isn't the BCLK master. Or you could move the last "Set sync period"
block up top, and do an early return if it's not the master. Either
way I think it's better than having a large indented block.

On the other hand, do the settings need to be cleared if it's the
slave?

ChenYu

>
>         /* Set sync period */
>         if (i2s->variant->has_fmt_set_lrck_period)
> @@ -501,10 +509,12 @@ static int sun4i_i2s_set_fmt(struct snd_soc_dai *dai, unsigned int fmt)
>                 case SND_SOC_DAIFMT_CBS_CFS:
>                         /* BCLK and LRCLK master */
>                         val = SUN4I_I2S_CTRL_MODE_MASTER;
> +                       i2s->bit_clk_master = true;
>                         break;
>                 case SND_SOC_DAIFMT_CBM_CFM:
>                         /* BCLK and LRCLK slave */
>                         val = SUN4I_I2S_CTRL_MODE_SLAVE;
> +                       i2s->bit_clk_master = false;
>                         break;
>                 default:
>                         dev_err(dai->dev, "Unsupported slave setting: %d\n",
> @@ -525,10 +535,12 @@ static int sun4i_i2s_set_fmt(struct snd_soc_dai *dai, unsigned int fmt)
>                         /* BCLK and LRCLK master */
>                         val = SUN8I_I2S_CTRL_BCLK_OUT |
>                                 SUN8I_I2S_CTRL_LRCK_OUT;
> +                       i2s->bit_clk_master = true;
>                         break;
>                 case SND_SOC_DAIFMT_CBM_CFM:
>                         /* BCLK and LRCLK slave */
>                         val = 0;
> +                       i2s->bit_clk_master = false;
>                         break;
>                 default:
>                         dev_err(dai->dev, "Unsupported slave setting: %d\n",
> --
> 2.16.0
>
> --
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