linux-kernel - Re: [PATCHv4 7/9] ASoC: fsl-asoc-card: add DT clock "cpu

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Date: Fri, 17 May 2024 05:05:35 -0400 (EDT)
From: Elinor Montmasson <elinor.montmasson@...oirfairelinux.com>
To: Mark Brown <broonie@...nel.org>
Cc: Liam Girdwood <lgirdwood@...il.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Conor Dooley <conor+dt@...nel.org>, 
	shengjiu wang <shengjiu.wang@...il.com>, 
	Xiubo Lee <Xiubo.Lee@...il.com>, Fabio Estevam <festevam@...il.com>, 
	Nicolin Chen <nicoleotsuka@...il.com>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, 
	linux-sound <linux-sound@...r.kernel.org>, 
	devicetree <devicetree@...r.kernel.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>, 
	alsa-devel <alsa-devel@...a-project.org>, 
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCHv4 7/9] ASoC: fsl-asoc-card: add DT clock "cpu_sysclk"
 with generic codec

From: "Mark Brown" <broonie@...nel.org>
Sent: Thursday, 16 May, 2024 14:13:19
> On Wed, May 15, 2024 at 03:54:09PM +0200, Elinor Montmasson wrote:
> 
>> Add an optional DT clock "cpu_sysclk" to get the CPU DAI system-clock
>> frequency when using the generic codec.
>> It is set for both Tx and Rx.
>> The way the frequency value is used is up to the CPU DAI driver
>> implementation.
> 
>> +		struct clk *cpu_sysclk = clk_get(&pdev->dev, "cpu_sysclk");
>> +		if (!IS_ERR(cpu_sysclk)) {
>> +			priv->cpu_priv.sysclk_freq[TX] = clk_get_rate(cpu_sysclk);
>> +			priv->cpu_priv.sysclk_freq[RX] = priv->cpu_priv.sysclk_freq[TX];
>> +			clk_put(cpu_sysclk);
>> +		}
> 
> I don't really understand the goal here - this is just reading whatever
> frequency happens to be set in the hardware when the driver starts up
> which if nothing else seems rather fragile?

The driver allow to set the sysclk frequency
of the CPU DAI through `priv->cpu_priv.sysclk_freq` when calling
`fsl_asoc_card_hw_params()`.
Currently it is hard-coded per use-case in the driver.

My reasoning was that with a generic codec/compatible, there might
be use-cases needing to use this parameter, so I exposed it here via DT.

Is it a bad idea to expose this parameter ? This is not a requirement for the
driver to work, most of the current compatibles do not use this parameter.
It is currently used only for `fsl,imx-audio-cs42888`.
In that case I can remove this commit.

Best regards,
Elinor Montmasson