linux-kernel - Re: [PATCH v1 04/10] ASoC: tegra: Support RT5631 by machine driver

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Message-ID: <Y/VEUaOIE1mk1utt@sirena.org.uk>
Date:   Tue, 21 Feb 2023 22:23:13 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Svyatoslav Ryhel <clamor95@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        Dmitry Osipenko <digetx@...il.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        linux-tegra@...r.kernel.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH v1 04/10] ASoC: tegra: Support RT5631 by machine driver

On Tue, Feb 21, 2023 at 08:32:05PM +0200, Svyatoslav Ryhel wrote:

> Add Realtek ALC5631/RT5631 codec support to the Tegra ASoC machine driver.
> The RT5631 codec is found on devices like ASUS Transformer TF201, TF700T
> and other Tegra-based Android tablets.
> 
> Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
> Signed-off-by: Ion Agorria <ion@...rria.com>

Your signoff should be last if you're the one sending this.

> +static unsigned int tegra_machine_mclk_rate_6mhz(unsigned int srate)
> +{
> +	unsigned int mclk;
> +
> +	switch (srate) {
> +	case 64000:
> +	case 88200:
> +	case 96000:
> +		mclk = 128 * srate;
> +		break;
> +	default:
> +		mclk = 256 * srate;
> +		break;
> +	}
> +	/* FIXME: Codec only requires >= 3MHz if OSR==0 */
> +	while (mclk < 6000000)
> +		mclk *= 2;

It feels like this is complicated enough and looks like the
clocking is flexible enough that it might be easier to just have
a table of values or otherwise enumerate standard rates, seeing
the code I feel like I need to worry about what happens if we
pick a clock rate over 6MHz (the loop could give a value over
that), and it's not clear why we have the switch statement rather
than just starting at a multiple of 128 and looping an extra time.

I suspect there's going to be no meaningful downside for having
the clock held at over 3MHz on a tablet form factor, the usual
issue would be power consumption but between the larger battery
size you tend to have on a tablet and the power draw of the
screen if that's on it's likely to be into the noise practially
speaking.

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