linux-kernel - Re: [RFC PATCH v2 5/5] ASoC: apple: Add macaudio machine driver

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Message-ID: <YqH2uCgaedf0HQPE@sirena.org.uk>
Date:   Thu, 9 Jun 2022 14:33:44 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Martin Povišer <povik+lin@...ebit.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Kettenis <kettenis@...nbsd.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>, asahi@...ts.linux.dev
Subject: Re: [RFC PATCH v2 5/5] ASoC: apple: Add macaudio machine driver

On Mon, Jun 06, 2022 at 09:19:10PM +0200, Martin Povišer wrote:

> +		/*
> +		 * Primary FE
> +		 *
> +		 * The mclk/fs ratio at 64 for the primary frontend is important
> +		 * to ensure that the headphones codec's idea of left and right
> +		 * in a stereo stream over I2S fits in nicely with everyone else's.
> +		 * (This is until the headphones codec's driver supports
> +		 * set_tdm_slot.)
> +		 *
> +		 * The low mclk/fs ratio precludes transmitting more than two
> +		 * channels over I2S, but that's okay since there is the secondary
> +		 * FE for speaker arrays anyway.
> +		 */
> +		.mclk_fs = 64,
> +	},

This seems weird - it looks like it's confusing MCLK and the bit clock
for the audio bus.  These are two different clocks.  Note that it's very
common for devices to require a higher MCLK/fs ratio to deliver the best
audio performance, 256fs is standard.

> +	{
> +		/*
> +		 * Secondary FE
> +		 *
> +		 * Here we want frames plenty long to be able to drive all
> +		 * those fancy speaker arrays.
> +		 */
> +		.mclk_fs = 256,
> +	}

Same thing here - this is at least confusing MCLK and the bit clock.

> +static bool macaudio_match_kctl_name(const char *pattern, const char *name)
> +{
> +	if (pattern[0] == '*') {
> +		int namelen, patternlen;
> +
> +		pattern++;
> +		if (pattern[0] == ' ')
> +			pattern++;
> +
> +		namelen = strlen(name);
> +		patternlen = strlen(pattern);
> +
> +		if (namelen > patternlen)
> +			name += (namelen - patternlen);
> +	}
> +
> +	return !strcmp(name, pattern);
> +}
> +
> +static int macaudio_limit_volume(struct snd_soc_card *card,
> +				 const char *pattern, int max)
> +{
> +	struct snd_kcontrol *kctl;
> +	struct soc_mixer_control *mc;
> +	int found = 0;
> +
> +	list_for_each_entry(kctl, &card->snd_card->controls, list) {
> +		if (!macaudio_match_kctl_name(pattern, kctl->id.name))
> +			continue;
> +
> +		found++;
> +		dev_dbg(card->dev, "limiting volume on '%s'\n", kctl->id.name);
> +
> +		/*
> +		 * TODO: This doesn't decrease the volume if it's already
> +		 * above the limit!
> +		 */
> +		mc = (struct soc_mixer_control *)kctl->private_value;
> +		if (max <= mc->max)
> +			mc->platform_max = max;
> +
> +	}
> +
> +	return found;
> +}

This shouldn't be open coded in a driver, please factor it out into the
core so we've got an API for "set limit X on control Y" then call that.

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