[PATCH v2] ASoC: fsl_ssi: Fix bclk calculation for mono channel

[Nicolin Chen]

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 at 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 at 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.