linux-kernel - Re: [PATCH v2] ASoC: fsl-asoc-card: Remove fsl_asoc_card_set_bias

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Message-ID: <20200802064351.GA24213@Asurada-Nvidia>
Date:   Sat, 1 Aug 2020 23:43:52 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@...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>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ASoC: fsl-asoc-card: Remove
 fsl_asoc_card_set_bias_level function

On Sun, Aug 02, 2020 at 10:22:35AM +0800, Shengjiu Wang wrote:

> > > +     /* Specific configuration for PLL */
> > > +     if (codec_priv->pll_id && codec_priv->fll_id) {
> > > +             if (priv->sample_format == SNDRV_PCM_FORMAT_S24_LE)
> > > +                     pll_out = priv->sample_rate * 384;
> > > +             else
> > > +                     pll_out = priv->sample_rate * 256;
> > > +
> > > +             ret = snd_soc_dai_set_pll(asoc_rtd_to_codec(rtd, 0),
> > > +                                       codec_priv->pll_id,
> > > +                                       codec_priv->mclk_id,
> > > +                                       codec_priv->mclk_freq, pll_out);
> > > +             if (ret) {
> > > +                     dev_err(dev, "failed to start FLL: %d\n", ret);
> > > +                     goto out;
> > > +             }
> > > +
> > > +             ret = snd_soc_dai_set_sysclk(asoc_rtd_to_codec(rtd, 0),
> > > +                                          codec_priv->fll_id,
> > > +                                          pll_out, SND_SOC_CLOCK_IN);
> >
> > Just came into my mind: do we need some protection here to prevent
> > PLL/SYSCLK reconfiguration if TX/RX end up with different values?
> >
> Sorry,  not really catching your point. could you please elaborate?
> Why do TX/RX end up with different values?

If TX and RX run concurrently but in different sample rates or
sample formats, pll_out would be overwritten to PLL/SYSCLK?

I remember imx-wm8962 uses SSI, having symmetric flags for rates/
channels/samplebits, but fsl-asoc-card might have (or will have)
other use case.

If all existing combinations don't have any problem, we can add
a protection later when we need.