linux-kernel - Re: [PATCH] sound/soc/codecs/wm8978: add missing BCLK divider setup

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Message-ID: <aOUDbF/i4+9PXc1j@opensource.cirrus.com>
Date: Tue, 7 Oct 2025 13:11:24 +0100
From: Charles Keepax <ckeepax@...nsource.cirrus.com>
To: Sune Brian <briansune@...il.com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sound/soc/codecs/wm8978: add missing BCLK divider setup

On Tue, Oct 07, 2025 at 07:22:10PM +0800, Sune Brian wrote:
> Charles Keepax <ckeepax@...nsource.cirrus.com> 於 2025年10月7日 週二 下午6:30寫道：
> > On Fri, Oct 03, 2025 at 05:13:04PM +0800, Brian Sune wrote:
> > > The original WM8978 codec driver did not set the BCLK (bit clock)
> > > divider, which can cause audio clocks to be incorrect or unstable
> > > depending on the sample rate and word length.
> >
> > This isn't totally accurate, the driver expects it will be set
> > through the set_clkdiv callback. Which one could probably argue
> > is a bit of a more legacy approach, but probably worth calling
> > that out here.
> 
> According to actual hardware tests and the WM8978 driver study.
> There are no bclk register setup in the entire driver. So I am not sure
> How could this even set through the callback? The IC itself requires
> 2-wires register load and this can't be done via software level.

/*
 * Configure WM8978 clock dividers.
 */
static int wm8978_set_dai_clkdiv(struct snd_soc_dai *codec_dai,
				 int div_id, int div)
{
	struct snd_soc_component *component = codec_dai->component;
	struct wm8978_priv *wm8978 = snd_soc_component_get_drvdata(component);
	int ret = 0;

	switch (div_id) {
	case WM8978_OPCLKRATE:
		...
	case WM8978_BCLKDIV:
		if (div & ~0x1c)
			return -EINVAL;
		snd_soc_component_update_bits(component, WM8978_CLOCKING, 0x1c, div); <<---- HERE
		break;
	default:
		return -EINVAL;
	}

	dev_dbg(component->dev, "%s: ID %d, value %u\n", __func__, div_id, div);

	return ret;
}

Its not missing its right there. That said your way is probably
slightly more standard these days, but we should take care of the
interaction between the two.

Thanks,
Charles