linux-kernel - Re: [PATCH v2 1/3] ASoC: wm8782: Handle maximum audio rate at runtime

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Message-ID: <20230914093731.GS103419@ediswmail.ad.cirrus.com>
Date:   Thu, 14 Sep 2023 09:37:31 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     John Watts <contact@...kia.org>
CC:     <alsa-devel@...a-project.org>, Liam Girdwood <lgirdwood@...il.com>,
        "Mark Brown" <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, <patches@...nsource.cirrus.com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] ASoC: wm8782: Handle maximum audio rate at runtime

On Thu, Sep 14, 2023 at 07:27:03PM +1000, John Watts wrote:
> On Thu, Sep 14, 2023 at 09:21:07AM +0000, Charles Keepax wrote:
> > On Thu, Sep 14, 2023 at 03:15:50AM +1000, John Watts wrote:
> > > The wm8782 supports up to 192kHz audio when pins are set correctly.
> > > Instead of hardcoding which rates are supported enable them all
> > > then refer to a max_rate variable at runtime.
> > > 
> > > Signed-off-by: John Watts <contact@...kia.org>
> > > ---
> > > +static int wm8782_dai_hw_params(struct snd_pcm_substream *component,
> > > +			    struct snd_pcm_hw_params *params,
> > > +			    struct snd_soc_dai *dai)
> > > +{
> > > +	struct wm8782_priv *priv =
> > > +		snd_soc_component_get_drvdata(dai->component);
> > > +
> > > +	if (params_rate(params) > priv->max_rate)
> > > +		return -EINVAL;
> > > +
> > > +	return 0;
> > > +}
> > 
> > We should be setting this as a constraint in startup, rather
> > than returning an error in hw_params. That will let user-space
> > know the supported rates and allow it to resample if necessary.
> 
> How do you do this? The struct with the rate is statically defined.
> 

You can programmatically add additional constraints, commonly
this will be done from the startup callback on the DAI. See
something like arizona_startup in sound/soc/codecs/arizona.c for
an example, that enables 44.1/48k rates based on clocks but the
principle should be similar.

Thanks,
Charles