linux-kernel - Re: [PATCH 2/3] arm64: dts: ti: k3-am62p-j722s: enable the bxs-4-64

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Message-ID: <20250815011621.rrdurnk6ueexwldw@hertz>
Date: Thu, 14 Aug 2025 20:16:21 -0500
From: Nishanth Menon <nm@...com>
To: Randolph Sapp <rs@...com>
CC: <vigneshr@...com>, <kristo@...nel.org>, <robh@...nel.org>,
        <krzk+dt@...nel.org>, <conor+dt@...nel.org>, <d-gole@...com>,
        <afd@...com>, <bb@...com>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <detheridge@...com>, <matt.coster@...tec.com>,
        Michael Walle
	<mwalle@...nel.org>
Subject: Re: [PATCH 2/3] arm64: dts: ti: k3-am62p-j722s: enable the bxs-4-64

On 15:40-20250814, Randolph Sapp wrote:
> On Wed Aug 13, 2025 at 1:42 PM CDT, Nishanth Menon wrote:
> > On 12:56-20250813, Randolph Sapp wrote:
> > [...]
> >
> >> >> +		reg = <0x00 0x0fd80000 0x00 0x80000>;
> >> >> +		clocks = <&k3_clks 237 1>;
> >> >> +		clock-names = "core";
> >> >> +		assigned-clocks = <&k3_clks 237 1>;
> >> >> +		assigned-clock-rates = <800000000>;
> >
> > btw, as per https://www.ti.com/lit/ds/symlink/tda4aen-q1.pdf (page 86)
> > 720MHz when vdd_core is 0.75v (default)
> > and 800MHz when vdd_core is 0.85v
> >
> > 0.85v is set in the board dts and higher OPPs are enabled depending on
> > board capability.
> >
> > You might want to check the assigned-clock-rates based on data sheet,
> > default should'nt need a assigned-clock-rate.
> 
> Are you suggesting that we set assigned-clock-rates in the board dts instead, or
> do you just want to do away with assigned-clock-rates in general and eat the
> perf difference?

The higher frequency is possible unless you know that the board is setup
for the higher voltage. So, set it board device tree file.

Look at what we did with OPP-High support on AM625 for example. That
frequency can only be reliably achieved if vdd_core is 0.85v. And base
SoC dtsi must assume safe default (min voltage of 0.75v) as the node is
enabled by default.

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D
https://ti.com/opensource