linux-kernel - Re: [PATCH v2 2/2] arm64: dts: meson: remove CPU opps below 1GHz for SM1 boards

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Message-ID: <8211344a481dd40f260106bdd3f03bfb@kernel.org>
Date:   Thu, 10 Feb 2022 10:36:02 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Christian Hewitt <christianshewitt@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] arm64: dts: meson: remove CPU opps below 1GHz for
 SM1 boards

On 2022-02-10 10:06, Christian Hewitt wrote:
> Amlogic SM1 devices experience CPU stalls and random board wedges when
> the system idles and CPU cores clock down to lower opp points. Recent
> vendor kernels include a change to remove 100-250MHz and other distro
> sources also remove the 500/667MHz points. Unless all 100-667Mhz opps
> are removed or the CPU governor forced to performance stalls are still
> observed, so let's remove them to improve stability and uptime.
> 
> Fixes: 3d9e76483049 ("arm64: dts: meson-sm1-sei610: enable DVFS")
> Signed-off-by: Christian Hewitt <christianshewitt@...il.com>
> ---
>  arch/arm64/boot/dts/amlogic/meson-sm1.dtsi | 20 --------------------
>  1 file changed, 20 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/amlogic/meson-sm1.dtsi
> b/arch/arm64/boot/dts/amlogic/meson-sm1.dtsi
> index 3c07a89bfd27..80737731af3f 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-sm1.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-sm1.dtsi
> @@ -95,26 +95,6 @@
>  		compatible = "operating-points-v2";
>  		opp-shared;
> 
> -		opp-100000000 {
> -			opp-hz = /bits/ 64 <100000000>;
> -			opp-microvolt = <730000>;
> -		};
> -
> -		opp-250000000 {
> -			opp-hz = /bits/ 64 <250000000>;
> -			opp-microvolt = <730000>;
> -		};
> -
> -		opp-500000000 {
> -			opp-hz = /bits/ 64 <500000000>;
> -			opp-microvolt = <730000>;
> -		};
> -
> -		opp-667000000 {
> -			opp-hz = /bits/ 64 <666666666>;
> -			opp-microvolt = <750000>;
> -		};
> -
>  		opp-1000000000 {
>  			opp-hz = /bits/ 64 <1000000000>;
>  			opp-microvolt = <770000>;

That's not nearly enough. If that's an actual issue, the driver
should be updated not to use these OPPs, and you can't assume
that people will just update their DT (mine comes from u-boot,
and it is unlikely I will update it anytime soon).

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...