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From:   Shengjiu Wang <shengjiu.wang@gmail.com>
Date:   Tue, 16 Jun 2020 10:13:35 +0800
Message-ID: <CAA+D8AMnCqzRRXFQ6rENbU5nTSuJpjd58t+Dhh+rpamoHjg7YA@mail.gmail.com>
Subject: Re: [PATCH v2] ASoC: fsl_ssi: Fix bclk calculation for mono channel
To:     Nicolin Chen <nicoleotsuka@gmail.com>
Cc:     Shengjiu Wang <shengjiu.wang@nxp.com>,
        Linux-ALSA <alsa-devel@alsa-project.org>,
        Timur Tabi <timur@kernel.org>, Xiubo Li <Xiubo.Lee@gmail.com>,
        linuxppc-dev@lists.ozlabs.org, Takashi Iwai <tiwai@suse.com>,
        Mark Brown <broonie@kernel.org>,
        Fabio Estevam <festevam@gmail.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Tue, Jun 16, 2020 at 9:59 AM Nicolin Chen <nicoleotsuka@gmail.com> wrote:
>
> On Tue, Jun 16, 2020 at 09:48:39AM +0800, Shengjiu Wang wrote:
> > On Tue, Jun 16, 2020 at 7:11 AM Nicolin Chen <nicoleotsuka@gmail.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@nxp.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.
>
> I think you have a point. Then would this condition work?
>
> +       /* ...but force 32 bits for stereo audio using I2S Master Mode */
> +       if (channels == 2 &&
> +           ssi->i2s_net & SSI_SCR_I2S_MODE_MASK == SSI_SCR_I2S_MODE_MASTER)
>
> Similar to yours but the code above it could look straightforward.

I think it should work.