linux-kernel - Re: [PATCH] ASoC: fsl_sai: Set SAI Channel Mode to Output Mode

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Message-ID: <20190902155218.GC5819@sirena.co.uk>
Date:   Mon, 2 Sep 2019 16:52:18 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Daniel Baluta <daniel.baluta@...il.com>
Cc:     Daniel Baluta <daniel.baluta@....com>,
        Fabio Estevam <festevam@...il.com>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        "S.j. Wang" <shengjiu.wang@....com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Timur Tabi <timur@...nel.org>,
        Cosmin-Gabriel Samoila <gabrielcsmo@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Cosmin-Gabriel Samoila <cosmin.samoila@....com>
Subject: Re: [PATCH] ASoC: fsl_sai: Set SAI Channel Mode to Output Mode

On Mon, Sep 02, 2019 at 04:35:56PM +0300, Daniel Baluta wrote:
> On Mon, Sep 2, 2019 at 3:42 PM Mark Brown <broonie@...nel.org> wrote:

> > This patch seems to do this unconditionally.  This is fine for
> > configurations where the SoC is the only thing driving the bus but will
> > mean that for TDM configurations where something else also drives some
> > of the slots we'll end up with both devices driving simultaneously.  The
> > safest thing would be to set this only if TDM isn't configured.

> I thought that the SAI IP is the single owner of the audio data lines,
> so even in TDM
> mode SAI IP (which is inside SoC) is the only one adding data on the bus.

> Now, you say that there could be two devices driving some of he masked
> slots right?

Doing that is the major point of TDM modes.  It could even be another
SAI on the same bus.

> I'm not sure how to really figure out that SAI is running in TDM mode.

As a first approximation you could just check if set_tdm_slots() has
been called, it might still be the only device but it's a good first
guess.

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