linux-kernel - Re: [PATCH v3] ASoC: wm8978: add missing BCLK divider setup

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Message-ID: <e78c9cc0-4a1f-4a22-9cba-a8213a7b9301@sirena.org.uk>
Date: Wed, 8 Oct 2025 13:12:39 +0100
From: Mark Brown <broonie@...nel.org>
To: Sune Brian <briansune@...il.com>
Cc: Charles Keepax <ckeepax@...nsource.cirrus.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ASoC: wm8978: add missing BCLK divider setup

On Tue, Oct 07, 2025 at 11:55:29PM +0800, Sune Brian wrote:
> Charles Keepax <ckeepax@...nsource.cirrus.com> 於 2025年10月7日 週二 下午11:21寫道：

> > Apologies but just realised there is still one small problem here.
> > You want to match the closest BCLK that is over your target rate,
> > if the BCLK is too slow the system won't work. As your bclk_divs
> > array is sorted I think you can do something like:

> Not too understand what is the issue.
> The idea is setting the initial value to max any diff that is smaller
> will update bclkdiv index,
> If the maximum LUT 32 still not met then it is what it is.
> mclk / 32 is the bclk, unless you want an error message.

Consider the case where the BCLK needed is 100 and SYSCLK is 198.
Dividing by 1 will result in an absolute difference of 98 and a BCLK of
198 while dividing by 2 will result in an absolute difference 1 and a
BCLK of 99 which is lower than the required BCLK.

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