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

[Neil Armstrong]

Hi Marc,

On 10/02/2022 11:36, Marc Zyngier wrote:
> 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@xxxxxxxxx>
> > ---
> >  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).

The driver is the generic cpufreq and a generic clock driver, we do not
filter out the possible OPP frequencies because the possible freq
is large and depends on the die revision.

I don't see why we should filter out these frequencies so far.

Neil

> Thanks,
>
>          M.