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

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Message-ID: <826f6c22-d1f1-42ce-a8d1-2d5cb894a970@sirena.org.uk>
Date: Fri, 31 May 2024 14:05:28 +0100
From: Mark Brown <broonie@...nel.org>
To: Elinor Montmasson <elinor.montmasson@...oirfairelinux.com>
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

On Fri, May 31, 2024 at 08:46:55AM -0400, Elinor Montmasson wrote:
> From: "Mark Brown" <broonie@...nel.org>
> > On Fri, May 17, 2024 at 05:05:35AM -0400, Elinor Montmasson wrote:
> >> From: "Mark Brown" <broonie@...nel.org>
> >> > On Wed, May 15, 2024 at 03:54:09PM +0200, Elinor Montmasson wrote:

> >> >> +		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.

> > I'm having a hard time connecting your reply here with my comment.  This
> > isn't as far as I can see allowing the frequency to be explicitly
> > configured, it's just using whatever value happens to be programmed in
> > the clock when the driver starts.

> In v3 I used parameters `cpu-sysclk-freq-rx/tx` to explicitly
> set the frequency.
> In its review Rob Herring said that the clock bindings should
> be used, so that's why I changed it to use this `cpu_sysclk` clock.

So you're trying to use this as the audio clock?  There's no code that
enables the clock which seems worrying, and I'd expect that if the
device is using it's own clock the device would be querying it directly
via the clock API rather than this.  This all seems really confused.

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