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

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Date: Fri, 17 May 2024 12:17:20 +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 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.

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