linux-kernel - Re: [PATCH] ASoC: fsl_sai: Clean code for synchronize mode

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Date:   Tue, 4 Aug 2020 09:39:44 +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>,
        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] ASoC: fsl_sai: Clean code for synchronize mode

On Tue, Aug 4, 2020 at 5:57 AM Nicolin Chen <nicoleotsuka@...il.com> wrote:
>
> On Mon, Aug 03, 2020 at 04:04:23PM +0800, Shengjiu Wang wrote:
>
> > > > clock generation. The TCSR.TE is no need to enabled when only RX
> > > > is enabled.
> > >
> > > You are correct if there's only RX running without TX joining.
> > > However, that's something we can't guarantee. Then we'd enable
> > > TE after RE is enabled, which is against what RM recommends:
> > >
> > > # From 54.3.3.1 Synchronous mode in IMX6SXRM
> > > # If the receiver bit clock and frame sync are to be used by
> > > # both the transmitter and receiver, it is recommended that
> > > # the receiver is the last enabled and the first disabled.
> > >
> > > I remember I did this "ugly" design by strictly following what
> > > RM says. If hardware team has updated the RM or removed this
> > > limitation, please quote in the commit logs.
> >
> > There is no change in RM and same recommandation.
> >
> > My change does not violate the RM. The direction which generates
> > the clock is still last enabled.
>
> Using Tx syncing with Rx clock for example,
> T1: arecord (non-stop) => set RE
> T2: aplay => set TE then RE (but RE is already set at T1)
>
> Anything that I am missing?

This is a good example.
We have used this change locally for a long time, so I think it is
safe to do this change, a little different with the recommandation.

>
> > > > +             if (!sai->synchronous[TX] && sai->synchronous[RX] && !tx) {
> > > > +                     regmap_update_bits(sai->regmap, FSL_SAI_xCSR((!tx), ofs),
> > > > +                                        FSL_SAI_CSR_TERE, FSL_SAI_CSR_TERE);
> > > > +             } else if (!sai->synchronous[RX] && sai->synchronous[TX] && tx) {
> > > > +                     regmap_update_bits(sai->regmap, FSL_SAI_xCSR((!tx), ofs),
> > > > +                                        FSL_SAI_CSR_TERE, FSL_SAI_CSR_TERE);
> > >
> > > Two identical regmap_update_bits calls -- both on !tx (RX?)
> > The content for regmap_update_bits is the same, but the precondition
> > is different.
> > The first one is for tx=false and enable TCSR.TE. (TX generate clock)
> > The second one is for tx=true and enable RSCR.RE (RX generate clock)
>
> Why not merge them?
>
> +               if ((!sai->synchronous[TX] && sai->synchronous[RX] && !tx) ||
> +                  ((!sai->synchronous[RX] && sai->synchronous[TX] && tx) {

oh, yes, good point!

best regards
wang shengjiu