linux-kernel - Re: [PATCH v2] arm64: dts: rockchip: Add OPP voltage ranges to RK3399 OP1 SoC dtsi

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Message-ID: <f6bb3387-4396-45d4-9cb4-594d58095510@cherry.de>
Date: Wed, 6 Nov 2024 10:32:06 +0100
From: Quentin Schulz <quentin.schulz@...rry.de>
To: Dragan Simic <dsimic@...jaro.org>, linux-rockchip@...ts.infradead.org
Cc: heiko@...ech.de, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, alchark@...il.com
Subject: Re: [PATCH v2] arm64: dts: rockchip: Add OPP voltage ranges to RK3399
 OP1 SoC dtsi

Hi Dragan,

On 11/6/24 9:33 AM, Dragan Simic wrote:
> Add support for voltage ranges to the CPU, GPU and DMC OPPs defined in the
> SoC dtsi for Rockchip OP1, as a variant of the Rockchip RK3399.  This may be
> useful if there are any OP1-based boards whose associated voltage regulators
> are unable to deliver the exact voltages; otherwise, it causes no functional
> changes to the resulting OPP voltages at runtime.
> 
> These changes cannot cause stability issues or any kind of damage, because
> it's perfectly safe to use the highest voltage from an OPP group for each OPP
> in the same group.  The only possible negative effect of using higher voltages
> is wasted energy in form of some additionally generated heat.
> 
> Reported-by: Quentin Schulz <quentin.schulz@...rry.de>

Well, I merely highlighted that the voltage was different on OP1 
compared to RK3399 for the 600MHz OPP :)

So... If there's ONE SoC I'm pretty sure is working as expected it's the 
OP1 fitted on the Gru Chromebooks with the ChromiumOS kernel fork 
(though yes, I believe all Gru CB are EoL since August 2023). In the 6.1 
kernel fork, there's also no range: 
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/refs/heads/chromeos-6.1/arch/arm64/boot/dts/rockchip/rk3399-op1-opp.dtsi

So not sure we need to handle theoretical cases here. Will let 
maintainers decide on that one. FWIW, there are two other OP1 devices, 
the RockPi4A+ and RockPi4B+ which do not change the OPP either.

Cheers,
Quentin