Re: [PATCH v3 11/18] arm64: dts: mediatek: mt8192-asurada: Couple VGPU and VSRAM_OTHER regulators

[AngeloGioacchino Del Regno]

Il 01/03/23 05:53, Chen-Yu Tsai ha scritto:
> On Tue, Feb 28, 2023 at 6:47 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@xxxxxxxxxxxxx> wrote:
> > Add coupling for these regulators, as VSRAM_OTHER is used to power the
> > GPU SRAM, and they have a strict voltage output relation to satisfy in
> > order to ensure GPU stable operation.
> > While at it, also add voltage constraint overrides for the GPU SRAM
> > regulator "mt6359_vsram_others", but don't touch mt6315's vbuck1 as
> > its constraints are fine.
>
> The minimum voltage on vbuck1 matches the lowest OPP. However the maximum
> voltage is set to the maximum of the regulator itself. The MT8192 datasheet
> says the absolute maximum for the GPU is 0.8V, and the recommended range
> for 0.8V is 0.72V ~ 0.88V. The highest OPP we have is 0.8V, so I would
> just set the maximum voltage to that?

The point was that we'd never get vbuck1 at more than vsram+10mV because
of the constraints that are set with regulator-coupled-max-spread, but
thinking about it again, relying on that is *highly* suboptimal.

Yes, you're right, let's change the constraints on vbuck1 to 800mV: that's
going to be for v4.

Thanks!
Angelo

> ChenYu
>
> > Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
> > ---
> >   arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
> > index df477eb89f21..c8b6e1a9605b 100644
> > --- a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
> > +++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
> > @@ -447,6 +447,13 @@ &mt6359_vrf12_ldo_reg {
> >          regulator-always-on;
> >   };
> >
> > +&mt6359_vsram_others_ldo_reg {
> > +       regulator-min-microvolt = <750000>;
> > +       regulator-max-microvolt = <850000>;
> > +       regulator-coupled-with = <&mt6315_7_vbuck1>;
> > +       regulator-coupled-max-spread = <10000>;
> > +};
> > +
> >   &mt6359_vufs_ldo_reg {
> >          regulator-always-on;
> >   };
> > @@ -1411,6 +1418,8 @@ mt6315_7_vbuck1: vbuck1 {
> >                                  regulator-max-microvolt = <1193750>;
> >                                  regulator-enable-ramp-delay = <256>;
> >                                  regulator-allowed-modes = <0 1 2>;
> > +                               regulator-coupled-with = <&mt6359_vsram_others_ldo_reg>;
> > +                               regulator-coupled-max-spread = <10000>;
> >                          };
> >                  };
> >          };
> > --
> > 2.39.2