linux-kernel - Re: [PATCH v2 1/1] arm64: dts: rockchip: rk3528: Add CPU frequency scaling support

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Message-Id: <20250730132026.214754-1-amadeus@jmu.edu.cn>
Date: Wed, 30 Jul 2025 21:20:26 +0800
From: Chukun Pan <amadeus@....edu.cn>
To: w@....eu
Cc: alchark@...il.com,
	amadeus@....edu.cn,
	conor+dt@...nel.org,
	devicetree@...r.kernel.org,
	heiko@...ech.de,
	jonas@...boo.se,
	krzk+dt@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-rockchip@...ts.infradead.org,
	ziyao@...root.org
Subject: Re: [PATCH v2 1/1] arm64: dts: rockchip: rk3528: Add CPU frequency scaling support

Hi,

> My point is that if you disable cpufreq, the CPU is running at 1.2V, which
> is even higher. I don't know why it's running at this voltage, maybe as
> the result of initializing some regulators, but that's what we're getting.
> So the question about safety of running between 1.13-1.15 resolves to
> "it's at least safer than running without cpufreq" in the current state.
>
> And as I mentioned it's clearly linux and not u-boot that is setting 1.2V,
> because under u-boot and during kernel selection and image loading, my
> board is at 0.95V. It's only once the kernel starts to boot that it bumps
> to 1.2V.

If opp-table is not configured, kernel will initialize the pwm-regulator
to maximum microvolts. This can be solved by configuring the pwm-regulator
in U-Boot (waiting for U-Boot to synchronize the DT of kernel 6.16):

```
&vdd_arm {
	regulator-init-microvolt = <953000>;
};

&vdd_logic {
	regulator-init-microvolt = <900000>;
};
```

Thanks,
Chukun

--
2.25.1