linux-kernel - Re: [PATCH 1/2] ASoC: max98090: Add master clock handling

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Message-ID: <537E1D0A.6020303@wwwdotorg.org>
Date:	Thu, 22 May 2014 09:51:38 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Tushar Behera <tushar.behera@...aro.org>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
CC:	tiwai@...e.de, perex@...ex.cz, broonie@...nel.org,
	dianders@...omium.org, jerry.wong@...imintegrated.com
Subject: Re: [PATCH 1/2] ASoC: max98090: Add master clock handling

On 05/22/2014 03:17 AM, Tushar Behera wrote:
> If master clock is provided through device tree, then update
> the master clock frequency during set_sysclk.
> 
> Documentation has been updated to reflect the change.

> diff --git a/sound/soc/codecs/max98090.c b/sound/soc/codecs/max98090.c

> @@ -1929,6 +1930,11 @@ static int max98090_dai_set_sysclk(struct snd_soc_dai *dai,
>  	if (freq == max98090->sysclk)
>  		return 0;
>  
> +	if (!IS_ERR(max98090->mclk)) {
> +		freq = clk_round_rate(max98090->mclk, freq);
> +		clk_set_rate(max98090->mclk, freq);
> +	}

What are the intended semantics of set_sysclk()?
sound/soc/tegra/tegra_wm98090.c assumes that set_sysclk() is a
notification to the CODEC driver to tell it what rate the MCLK input is
set to (the rate is set before calling set_sysclk), whereas the code
above assumes that this function is to tell the CODEC to somehow
configure its input clock to be a particular rate. I have a feeling the
code above might fail on Tegra.

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