Fixed regulator without GPIO

Robotics & Edge Computing Jetson & Embedded Systems Jetson AGX Xavier
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1

Hi,

How are the fixed regulators get controlled (turn on/off) for the ones that has no GPIO binding in device-tree?

For example, the battery_reg:

hdr40_vdd_5v0: battery_reg: regulator@0 {
			compatible = "regulator-fixed";
			reg = <0>;
			regulator-name = "vdd-ac-bat";
			regulator-min-microvolt = <5000000>;
			regulator-max-microvolt = <5000000>;
			regulator-always-on;
		};

And p2822_vdd_fan:

p2822_vdd_fan: regulator@111 {
			compatible = "regulator-fixed";
			reg = <111>;
			regulator-name = "vdd-fan";
			regulator-min-microvolt = <5000000>;
			regulator-max-microvolt = <5000000>;
		};

The examples that I posted above has NO gpio = <XXX> binding. So, they cannot be turned on/off by GPIO. So, how are they get controlled? It would also be nice to understand it from devkit schematic as well.

Regards.

3

hello lunarking1028,

please check this topic for the definition in device tree to indicate the regulator names and its voltage.
you’re able to control it via kernel drivers.
thanks

4

Hi,

Thanks for your quick reply.
My question is about why it doesn’t have GPIO bindings in some of the fixed regulator.
Your link shows an example of how to use a GPIO binded fixed-regulator, which is NOT what I am looking for.

Also, the GPIO and fixed regulator in device-tree should match the hardware design.

Let me ask in a more specific way.
For example, the p2822_vdd_fan fixed regulator, it has NO GPIO for it:

p2822_vdd_fan: regulator@111 {
			compatible = "regulator-fixed";
			reg = <111>;
			regulator-name = "vdd-fan";
			regulator-min-microvolt = <5000000>;
			regulator-max-microvolt = <5000000>;
		};

And its consumer is the pwm-fan.

pwm-fan {
		vdd-fan-supply = <&p2822_vdd_fan>;
	}

When the fan is turned on/off, how its regulator get turned on/off? (fixed regulator, NO GPIO control) It seems it is a faked regulator?

Regards.

5

hello lunarking1028,

it’s an optional properties of GPIO to use for enable control,
please refer to kernel documentation,
for example, $L4T_Sources/r32.5.1/Linux_for_Tegra/source/public/kernel/kernel-4.9/Documentation/devicetree/bindings/regulator/fixed-regulator.txt
thanks

6

Hi,

As I said that “the GPIO and fixed regulator in device-tree should match the hardware design.” I cannot just pick any GPIO and put it there.

I checked devkit schematic, there is NO GPIO for enable/disable the power of fan. The fan’s power is VDD_5V which is enabled when carrier power is enabled.

So, again I still don’t see any need for that regulator there. Or It may be just a fake regulator to make the linux fan system happy.

Thanks.

7

Yes, it is just a fake one. It is for the driver because some drivers will check a regulator in their initialization.