linux-kernel - Re: [PATCH] ASoC: codecs: dmic: Use channel map for configs with a single mic

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Message-ID: <20180105120455.GA9076@sirena.org.uk>
Date:   Fri, 5 Jan 2018 12:04:55 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@...com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bhumika Goyal <bhumirks@...il.com>,
        huang lin <hl@...k-chips.com>,
        Brian Norris <briannorris@...omium.org>,
        Dylan Reid <dgreid@...omium.org>
Subject: Re: [PATCH] ASoC: codecs: dmic: Use channel map for configs with a
 single mic

On Fri, Jan 05, 2018 at 11:45:43AM +0100, Arnaud Pouliquen wrote:

> >> +             num-channels = <1>;

> In your implementation seems not linked to hardware but software...

> DMIC driver description specifies the channels_max to 8 channels.
> I suppose that it is used for DMIC codecs that integrate filters and are
> connected to CPU DAI with I2S/PCM links. But it can be also used for
> DMIC connected to CPU DAI with a SPI link (in this case decimation
> filter in on Soc side).

The intention with the DMIC CODEC is that it's used when the CPU
directly has PDM inputs and the DMICs are just directly wired to it
(stereo is obviously the norm here but some SoCs may bunch things up
further for use with mic arrays).

> If we continue to support both use cases, specify the number of channels
> seems reasonable but this should be use to change the max channel
> constraint, not to declare a control.

Yes, that would seem the most obvious thing - it's how we handle things
like CPU DAIs that support very high channel counts when connected to
stereo CODECs for example.  It's not obvious why we'd use a channel map
here instead.

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