[PATCH 0/2] arm64: dts: rockchip: Add pwm nodes for RK3528

[Chukun Pan]

Hi,

> Interesting, good that it works with the updated U-Boot. Main change
> compared to v1 is that it now use clock/reset id and DT closer to what
> has been merged in mainline Linux. It also has DT params to help
> initialize the two pwm regulators used by these boards.
>
> I will try with the old v1 U-Boot series and see if I can replicated
> your issue.

Hi, I found the reason. I did some experiments today:

pwm-regulator  pwm1 | pwm2 | pwm3
-----------------------------------
ArmSoM Sige1 |      | work | work |
Radxa E20C   | work | hang |      |
other 3528   | work | hang |      |

This looks weird, so I tested it further:

In the new series of u-boot:
```
--- a/arch/arm/dts/rk3528-radxa-e20c-u-boot.dtsi
+++ b/arch/arm/dts/rk3528-radxa-e20c-u-boot.dtsi
@@ -8,9 +8,9 @@
 };
 
 &vdd_arm {
-	regulator-init-microvolt = <953000>;
+	status = "disabled"; # Cancel changes, pwm works
 };
 
 &vdd_logic {
-	regulator-init-microvolt = <900000>;
+	status = "disabled"; # Cancel changes, kernel hang
 };
```

I looked at schematic and found an interesting thing:
1. ArmSoM Sige1 schematic: VDD_LOGIC Default 0.901V
2. Radxa E20C schematic: VDD_LOGIC No default voltage

Therefore, the default voltage of VDD_LOGIC (supply to
GPU and LOGIC) needs to be set to 0.9V when initializing.

This can be done by hardware or software (such as u-boot)
Should we support this in the kernel driver of regulator?

Thanks,
Chukun

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2.25.1