linux-kernel - Re: [PATCH v2] ASoC: fsl_ssi: Fix bclk calculation for mono channel

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Message-ID: <CAA+D8ANK079rFL-_kwYKkn=nvrsBJPHW8bWMTwNCwDVzHt0PdA@mail.gmail.com>
Date:   Tue, 16 Jun 2020 09:48:39 +0800
From:   Shengjiu Wang <shengjiu.wang@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Shengjiu Wang <shengjiu.wang@....com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Timur Tabi <timur@...nel.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, Takashi Iwai <tiwai@...e.com>,
        Mark Brown <broonie@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ASoC: fsl_ssi: Fix bclk calculation for mono channel

On Tue, Jun 16, 2020 at 7:11 AM Nicolin Chen <nicoleotsuka@...il.com> wrote:
>
> On Mon, Jun 15, 2020 at 01:56:18PM +0800, Shengjiu Wang wrote:
> > For mono channel, SSI will switch to Normal mode.
> >
> > In Normal mode and Network mode, the Word Length Control bits
> > control the word length divider in clock generator, which is
> > different with I2S Master mode (the word length is fixed to
> > 32bit), it should be the value of params_width(hw_params).
> >
> > The condition "slots == 2" is not good for I2S Master mode,
> > because for Network mode and Normal mode, the slots can also
> > be 2. Then we need to use (ssi->i2s_net & SSI_SCR_I2S_MODE_MASK)
> > to check if it is I2S Master mode.
>
> The fsl_ssi_set_bclk is only called when fsl_ssi_is_i2s_master,
> though I agree that that line of comments sounds confusing now.

Actually I think fsl_ssi_is_i2s_master is not accurate, it just checks
the Master mode,  but didn't check the I2S mode.

>
> > So we refine the famula for mono channel, otherwise there
>
> famula => formula?
>
> > will be sound issue for S24_LE.
> >
> > Fixes: b0a7043d5c2c ("ASoC: fsl_ssi: Caculate bit clock rate using slot number and width")
> > Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> > ---
> > changes in v2
> > - refine patch for Network mode and Normal mode.
> >
> >  sound/soc/fsl/fsl_ssi.c | 15 +++++++++++----
> >  1 file changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
> > index bad89b0d129e..cbf67d132fda 100644
> > --- a/sound/soc/fsl/fsl_ssi.c
> > +++ b/sound/soc/fsl/fsl_ssi.c
> > @@ -678,7 +678,8 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
> >       struct regmap *regs = ssi->regs;
> >       u32 pm = 999, div2, psr, stccr, mask, afreq, factor, i;
> >       unsigned long clkrate, baudrate, tmprate;
> > -     unsigned int slots = params_channels(hw_params);
> > +     unsigned int channels = params_channels(hw_params);
> > +     unsigned int slots;
> >       unsigned int slot_width = 32;
> >       u64 sub, savesub = 100000;
> >       unsigned int freq;
> > @@ -688,9 +689,15 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
> >       /* Override slots and slot_width if being specifically set... */
> >       if (ssi->slots)
> >               slots = ssi->slots;
> > -     /* ...but keep 32 bits if slots is 2 -- I2S Master mode */
> > -     if (ssi->slot_width && slots != 2)
> > -             slot_width = ssi->slot_width;
> > +     else
> > +             /* Apply two slots for mono channel, because DC = 2 */
> > +             slots = (channels == 1) ? 2 : channels;
> > +
> > +     /* ...but keep 32 bits if I2S Master mode */
> > +     if ((ssi->i2s_net & SSI_SCR_I2S_MODE_MASK) != SSI_SCR_I2S_MODE_MASTER ||
> > +         channels == 1)
> > +             slot_width = ssi->slot_width ? ssi->slot_width :
>
> This looks very complicated...can you review and try mine?
> (Basically, take 32-bit out of default but force it later)
>
> @@ -678,8 +678,9 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
>         struct regmap *regs = ssi->regs;
>         u32 pm = 999, div2, psr, stccr, mask, afreq, factor, i;
>         unsigned long clkrate, baudrate, tmprate;
> -       unsigned int slots = params_channels(hw_params);
> -       unsigned int slot_width = 32;
> +       unsigned int channels = params_channels(hw_params);
> +       unsigned int slot_width = params_width(hw_params);
> +       unsigned int slots = 2;
>         u64 sub, savesub = 100000;
>         unsigned int freq;
>         bool baudclk_is_used;
> @@ -688,10 +689,16 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
>         /* Override slots and slot_width if being specifically set... */
>         if (ssi->slots)
>                 slots = ssi->slots;
> -       /* ...but keep 32 bits if slots is 2 -- I2S Master mode */
> -       if (ssi->slot_width && slots != 2)
> +       if (ssi->slot_width)
>                 slot_width = ssi->slot_width;
>
> +       /*
> +        * ...but force 32 bits for stereo audio. Note that mono audio is also
> +        * sent in 2 slots via NORMAL mode, so check both slots and channels.
> +        */
> +       if (slots == 2 && channels == 2)
> +               slot_width = 32;

slots ==2 && channels ==2 does not mean the I2S Master mode.
For LEFT_J, it is also slots =2 & channels = 2, then the slot_width
should be params_width(hw_params).
and DSP_A/B also supports stereo.