linux-kernel - ASoC: Question regarding device-tree multi-lane I2S for Allwinner SoC

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Date:   Sun, 1 Nov 2020 18:30:15 +0100
From:   Clément Péron <peron.clem@...il.com>
To:     Rob Herring <robh+dt@...nel.org>, Mark Brown <broonie@...nel.org>,
        Maxime Ripard <mripard@...nel.org>
Cc:     Jernej Škrabec <jernej.skrabec@...l.net>,
        Chen-Yu Tsai <wens@...e.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Marcus Cooper <codekipper@...il.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Samuel Holland <samuel@...lland.org>
Subject: ASoC: Question regarding device-tree multi-lane I2S for Allwinner SoC

Hi device-tree and sound Maintainers,

I have a question regarding multi-lane i2S representation.

On the Allwinner SoC the I2S/PCM Interface can handle up to four lanes
as output or input.
For each lane we can enable up to sixteen slots.
And for each output slot we can choose which slot to map.

The only representation I found is for Amlogic device-tree they did
the following sound node :
/* 8ch hdmi interface */
dai-link-7 {
    sound-dai = <&tdmif_b>;
    dai-format = "i2s";
    dai-tdm-slot-tx-mask-0 = <1 1>;
    dai-tdm-slot-tx-mask-1 = <1 1>;
    dai-tdm-slot-tx-mask-2 = <1 1>;
    dai-tdm-slot-tx-mask-3 = <1 1>;
    mclk-fs = <256>;

    codec {
        sound-dai = <&tohdmitx TOHDMITX_I2S_IN_B>;
    };
};

This kind of representation gives the information that 2 slots should
be enabled as TX per lane but don't give which slot to map.
I was thinking about a representation per lane but maybe it's a bit
complicated  ?

    dai-format = "dsp_a";
    dai-tdm-slot-width = <32>;
    // Lane 0 : Output 8 channels 0-7 using TDM
    dai-tdm-slot-tx-mask-0 = <1 1 1 1 1 1 1 1>;
    dai-tdm-slot-chmap-0 = <0 1 2 3 4 5 6 7>;
    // Lane 1 : Output 3 channels 5-7 using TDM
    dai-tdm-slot-tx-mask-1 = <1 1 1>;
    dai-tdm-slot-chmap-1 = <5 6 7>;

I will only start to support HDMI, so 4 I2S lanes for now it should
look like this

    dai-format = "i2s";
    dai-tdm-slot-width = <32>;
    frame-inversion;
    // Lane 0 : Output channels 0,1
    dai-tdm-slot-tx-mask-0 = <1 1>;
    dai-tdm-slot-chmap-0 = <0 1>;
    // Lane 1: Output channels 2,3
    dai-tdm-slot-tx-mask-1 = <1 1>;
    dai-tdm-slot-chmap-1 = <2 3>;
    // Lane 2: Output channels 4,5
    dai-tdm-slot-tx-mask-2 = <1 1>;
    dai-tdm-slot-chmap-2 = <4 5>;
    // Lane 3: Output channels 6,7
    dai-tdm-slot-tx-mask-3 = <1 1>;
    dai-tdm-slot-chmap-3 = <6 7>;

What do you think? Do you have any remark / idea about this ?

Thanks for your help
Clement