| Message ID | 20200825152551.1.I6d12081e37d27ba7580a1af877727d882935787a@changeid (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | CHROMIUM: arm64: dts: mt8183-elm: Set GPU power regulator to always on | expand |
:facepalm: sorry about the subject line. I'll fix it up in the next revision. On Tue, 25 Aug 2020 at 15:26, Anand K Mistry <amistry@google.com> wrote: > > Keep the da9212 BUCKB always-on. This works around an issue on Elm/Hana > devices where sometimes, the regulator is disabled before scpsys is > suspended, causing the suspension of scpsys to fail. > > Usually, the GPU and scpsys are suspended by the runtime PM before the > system is suspended, due to the GPU being idle. In this case, scpsys is > suspended inline with the GPU suspend, which then disables the > regulator. However, if the GPU is still active when system is suspended, > GPU suspend occurs but defers suspending scpsys to the PM's noirq phase. > Since GPU suspend disables the regulator, scpsys isn't powered and > suspending it fails with the following error: > [ 523.773227] mtk-scpsys 10006000.scpsys: Failed to power off domain mfg_2d > > On resume, scpsys is resumed in the noirq phase. Since scpsys requires > power from the regulator, which is still disabled at this point, > attempting to turn it on will hang the CPU. A HW watchdog eventually > reboots the system. > > The obvious solution would be to add a link to the regulator from scpsys > in the devicetree. This would prevent the regulator from being disabled > until scpsys is suspended. However, in the case where suspending scpsys > is deferred to the noirq phase, disabling the regulator will fail since > it is connected over I2C which requires IRQs to be enabled. Even in the > usual case where scpsys is suspended inline with the GPU, PM will always > attempt to resume scpsys in noirq. This will attempt to enable the > regulator, which will also fail due to being unable to communicate over > I2C. > > Since I2C can't be using with IRQs disabled, a workaround is to never > turn off the regulator. > > Measuring power on the GPU rail on a Elm DVT shows that the change in > power usage is negligible. The two relavent cases are S0 with an idle > GPU, and S3. > > In S0 with an idle GPU, current behaviour with the regulator off: > @@ NAME COUNT AVERAGE STDDEV MAX MIN > @@ gpu_mw 600 1.74 1.31 6.75 0.00 > ... and with the regulator on, but no load: > @@ NAME COUNT AVERAGE STDDEV MAX MIN > @@ gpu_mw 600 1.68 1.25 7.13 0.00 > The difference being well within the margin of error. > > In S3, current behaviour with the regulator off: > @@ NAME COUNT AVERAGE STDDEV MAX MIN > @@ gpu_mw 600 0.94 0.74 3.25 0.00 > ... and with the regulator on: > @@ NAME COUNT AVERAGE STDDEV MAX MIN > @@ gpu_mw 600 0.83 0.66 3.25 0.00 > > Signed-off-by: Anand K Mistry <amistry@google.com> > > --- > > arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi b/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi > index a5a12b2599a4..1294f27b21c1 100644 > --- a/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi > +++ b/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi > @@ -304,6 +304,7 @@ da9211_vgpu_reg: BUCKB { > regulator-min-microamp = <2000000>; > regulator-max-microamp = <3000000>; > regulator-ramp-delay = <10000>; > + regulator-always-on; > }; > }; > }; > -- > 2.28.0.297.g1956fa8f8d-goog >
diff --git a/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi b/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi index a5a12b2599a4..1294f27b21c1 100644 --- a/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi +++ b/arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi @@ -304,6 +304,7 @@ da9211_vgpu_reg: BUCKB { regulator-min-microamp = <2000000>; regulator-max-microamp = <3000000>; regulator-ramp-delay = <10000>; + regulator-always-on; }; }; };
Keep the da9212 BUCKB always-on. This works around an issue on Elm/Hana devices where sometimes, the regulator is disabled before scpsys is suspended, causing the suspension of scpsys to fail. Usually, the GPU and scpsys are suspended by the runtime PM before the system is suspended, due to the GPU being idle. In this case, scpsys is suspended inline with the GPU suspend, which then disables the regulator. However, if the GPU is still active when system is suspended, GPU suspend occurs but defers suspending scpsys to the PM's noirq phase. Since GPU suspend disables the regulator, scpsys isn't powered and suspending it fails with the following error: [ 523.773227] mtk-scpsys 10006000.scpsys: Failed to power off domain mfg_2d On resume, scpsys is resumed in the noirq phase. Since scpsys requires power from the regulator, which is still disabled at this point, attempting to turn it on will hang the CPU. A HW watchdog eventually reboots the system. The obvious solution would be to add a link to the regulator from scpsys in the devicetree. This would prevent the regulator from being disabled until scpsys is suspended. However, in the case where suspending scpsys is deferred to the noirq phase, disabling the regulator will fail since it is connected over I2C which requires IRQs to be enabled. Even in the usual case where scpsys is suspended inline with the GPU, PM will always attempt to resume scpsys in noirq. This will attempt to enable the regulator, which will also fail due to being unable to communicate over I2C. Since I2C can't be using with IRQs disabled, a workaround is to never turn off the regulator. Measuring power on the GPU rail on a Elm DVT shows that the change in power usage is negligible. The two relavent cases are S0 with an idle GPU, and S3. In S0 with an idle GPU, current behaviour with the regulator off: @@ NAME COUNT AVERAGE STDDEV MAX MIN @@ gpu_mw 600 1.74 1.31 6.75 0.00 ... and with the regulator on, but no load: @@ NAME COUNT AVERAGE STDDEV MAX MIN @@ gpu_mw 600 1.68 1.25 7.13 0.00 The difference being well within the margin of error. In S3, current behaviour with the regulator off: @@ NAME COUNT AVERAGE STDDEV MAX MIN @@ gpu_mw 600 0.94 0.74 3.25 0.00 ... and with the regulator on: @@ NAME COUNT AVERAGE STDDEV MAX MIN @@ gpu_mw 600 0.83 0.66 3.25 0.00 Signed-off-by: Anand K Mistry <amistry@google.com> --- arch/arm64/boot/dts/mediatek/mt8173-elm.dtsi | 1 + 1 file changed, 1 insertion(+)