linux-kernel - Re: [alsa-devel] [PATCH v2 1/2] ASoC: ak4118: Add support for AK4118 S/PDIF transceiver

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Message-ID: <CAJiuCcd_LAhODGGu=EBj4WBvx2PufcVbw=tO1+Mm+1Hj0k6BRw@mail.gmail.com>
Date:   Wed, 14 Nov 2018 16:24:44 +0100
From:   Clément Péron <peron.clem@...il.com>
To:     ricard.wanderlof@...s.com
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        alsa-devel@...a-project.org,
        Adrien Charruel <adrien.charruel@...ialet.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [alsa-devel] [PATCH v2 1/2] ASoC: ak4118: Add support for AK4118
 S/PDIF transceiver

Hi Ricard,

On Wed, 14 Nov 2018 at 16:07, Ricard Wanderlof
<ricard.wanderlof@...s.com> wrote:
>
>
> On Wed, 14 Nov 2018, Clément Péron wrote:
>
> > From: Adrien Charruel <adrien.charruel@...ialet.com>
> >
> > The AK4118A is a digital audio transceiver supporting 8 input channels
> > at 192kHz and with 24bits resolution.
> > It converts the S/PDIF signal to I2S format and is configurable over I2C.
> >
> > This driver introduce a minimal support of the AK4118, like selecting the
> > input channel, reading input frequency and detecting some errors.
>
> I'm curious, from what it seems, there is no checking that the input
> sample rate actually matches the configured sample rate? It's perfectly
> understandable for a driver which has 'minimal support', but it's
> something a user must be aware of; for instance if someone does
>
> arecord -r 48000 output.wav
>
> when the input data actually has a rate of 44100 Hz then the file will be
> written with a header specifying 44100 Hz but the data will actually be
> 48000 Hz.
>
> It's not an objection on my part, just an observation. I don't know how
> ALSA could enforce this in any way; ideally (barring automatic sample rate
> conversion) one would want an error message that the sample rate specified
> when opening the stream does not match the sample rate of the S/PDIF input
> data.

I'm quite new with linux audio driver but adding in ak4118_hw_params a
check like if params_rate(params) == ak4118_rate should do the job no
?

Regards,
Clement

>
> /Ricard
> --
> Ricard Wolf Wanderlof                           ricardw(at)axis.com
> Axis Communications AB, Lund, Sweden            www.axis.com
> Phone +46 46 272 2016                           Fax +46 46 13 61 30