linux-kernel - Re: [PATCH v3 1/9] ASoC: sun4i-i2s: Adjust regmap settings

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Date:   Sat, 22 Dec 2018 00:44:07 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Code Kipper <codekipper@...il.com>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        "Andrea Venturi (pers)" <be17068@...rbole.bo.it>
Subject: Re: [PATCH v3 1/9] ASoC: sun4i-i2s: Adjust regmap settings

On Fri, Dec 21, 2018 at 11:21 PM <codekipper@...il.com> wrote:
>
> From: Marcus Cooper <codekipper@...il.com>
>
> Bypass the regmap cache when flushing the i2s FIFOs and modify the tables
> to reflect this.
>
> Signed-off-by: Marcus Cooper <codekipper@...il.com>
> ---
>  sound/soc/sunxi/sun4i-i2s.c | 29 +++++++++--------------------
>  1 file changed, 9 insertions(+), 20 deletions(-)
>
> diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c
> index d5ec1a20499d..64d073cb2aee 100644
> --- a/sound/soc/sunxi/sun4i-i2s.c
> +++ b/sound/soc/sunxi/sun4i-i2s.c
> @@ -548,9 +548,11 @@ static int sun4i_i2s_set_fmt(struct snd_soc_dai *dai, unsigned int fmt)
>  static void sun4i_i2s_start_capture(struct sun4i_i2s *i2s)
>  {
>         /* Flush RX FIFO */
> +       regcache_cache_bypass(i2s->regmap, true);
>         regmap_update_bits(i2s->regmap, SUN4I_I2S_FIFO_CTRL_REG,
>                            SUN4I_I2S_FIFO_CTRL_FLUSH_RX,
>                            SUN4I_I2S_FIFO_CTRL_FLUSH_RX);
> +       regcache_cache_bypass(i2s->regmap, false);

IIRC the flush cache bit is self-clearing. So you likely want to mark
this register as volatile. If it is marked as volatile, then all access
to that register bypasses the cache, so the regcache_cache_bypass calls
are unneeded.

However, looking at the code, the write would seem to be ignored if the
regmap is in the cache_only state. We only set this when the bus clock
is disabled. Under such a condition, bypassing the cache and forcing a
write would be unwise, as the system either drops the write, or stalls
altogether.

>
>         /* Clear RX counter */
>         regmap_write(i2s->regmap, SUN4I_I2S_RX_CNT_REG, 0);
> @@ -569,9 +571,11 @@ static void sun4i_i2s_start_capture(struct sun4i_i2s *i2s)
>  static void sun4i_i2s_start_playback(struct sun4i_i2s *i2s)
>  {
>         /* Flush TX FIFO */
> +       regcache_cache_bypass(i2s->regmap, true);
>         regmap_update_bits(i2s->regmap, SUN4I_I2S_FIFO_CTRL_REG,
>                            SUN4I_I2S_FIFO_CTRL_FLUSH_TX,
>                            SUN4I_I2S_FIFO_CTRL_FLUSH_TX);
> +       regcache_cache_bypass(i2s->regmap, false);
>
>         /* Clear TX counter */
>         regmap_write(i2s->regmap, SUN4I_I2S_TX_CNT_REG, 0);
> @@ -703,13 +707,7 @@ static const struct snd_soc_component_driver sun4i_i2s_component = {
>
>  static bool sun4i_i2s_rd_reg(struct device *dev, unsigned int reg)
>  {
> -       switch (reg) {
> -       case SUN4I_I2S_FIFO_TX_REG:
> -               return false;
> -
> -       default:
> -               return true;
> -       }
> +       return true;

I don't understand why this is relevant. Do you need to read back from the TX
FIFO?

If so, just drop the call-back altogether. If no callback is provided and no
rd_table is provided either, it defaults to all registers under max_register
(if max_register < 0) are readable.

However this seems like it deserves to be a separate patch (where you explain
in the commit log why it's needed).

Regards
ChenYu

>  }
>
>  static bool sun4i_i2s_wr_reg(struct device *dev, unsigned int reg)
> @@ -728,6 +726,8 @@ static bool sun4i_i2s_volatile_reg(struct device *dev, unsigned int reg)
>  {
>         switch (reg) {
>         case SUN4I_I2S_FIFO_RX_REG:
> +       case SUN4I_I2S_FIFO_TX_REG:
> +       case SUN4I_I2S_FIFO_STA_REG:
>         case SUN4I_I2S_INT_STA_REG:
>         case SUN4I_I2S_RX_CNT_REG:
>         case SUN4I_I2S_TX_CNT_REG:
> @@ -738,23 +738,12 @@ static bool sun4i_i2s_volatile_reg(struct device *dev, unsigned int reg)
>         }
>  }
>
> -static bool sun8i_i2s_rd_reg(struct device *dev, unsigned int reg)
> -{
> -       switch (reg) {
> -       case SUN8I_I2S_FIFO_TX_REG:
> -               return false;
> -
> -       default:
> -               return true;
> -       }
> -}
> -
>  static bool sun8i_i2s_volatile_reg(struct device *dev, unsigned int reg)
>  {
>         if (reg == SUN8I_I2S_INT_STA_REG)
>                 return true;
>         if (reg == SUN8I_I2S_FIFO_TX_REG)
> -               return false;
> +               return true;
>
>         return sun4i_i2s_volatile_reg(dev, reg);
>  }
> @@ -809,7 +798,7 @@ static const struct regmap_config sun8i_i2s_regmap_config = {
>         .reg_defaults   = sun8i_i2s_reg_defaults,
>         .num_reg_defaults       = ARRAY_SIZE(sun8i_i2s_reg_defaults),
>         .writeable_reg  = sun4i_i2s_wr_reg,
> -       .readable_reg   = sun8i_i2s_rd_reg,
> +       .readable_reg   = sun4i_i2s_rd_reg,
>         .volatile_reg   = sun8i_i2s_volatile_reg,
>  };
>
> --
> 2.20.1
>