topic How did `echo mem > /sys/power/state ` do ? in i.MX Processors

How did `echo mem > /sys/power/state ` do ?

wangvictor — Wed, 29 Nov 2017 06:58:38 GMT

Hi All,

I'm using i.MX6 sabresd for my board and ubuntu 16.04 for my os system.

When I go into the sleeping mode I will run `echo mem > /sys/power/state `.

And the back light will turn off.

Here I got some questions:

1. Where will it turned off the back light when I run `echo mem > /sys/power/state ` and how do it know which back light pin I've defined.

2. Which device will it turned off ?

Any answers or documents can provide me to understand it?

Thanks in Advanced!

Re: How did `echo mem > /sys/power/state ` do ?

aravinthkumarja — Wed, 29 Nov 2017 13:00:47 GMT

Hi victor,

1) This is direct syscall. it will call the kernel functions and it will do the respective operation.

2) In kernel it will fetch pin details from dts. In dts configured device it get to off.

Regards,

Aravinth

Re: How did `echo mem > /sys/power/state ` do ?

wangvictor — Thu, 30 Nov 2017 02:30:52 GMT

@aravinthkumar jayaprakasam

1) Which kernel driver will it call could you give me a hint?

2) So if I defined it in the dts then it will be all set in the pmic detect?

Re: How did `echo mem > /sys/power/state ` do ?

art — Thu, 30 Nov 2017 09:31:02 GMT

Actually, when you execute the 'echo mem > /sys/power/state' command, the system goes to the "suspend-to-memory" power saving mode, turning most of the SoC IPs off. The display backlight is controlled by the backlight driver, you can check its definitions in the system .dts file.

You can find more information in the BSP documentation, please find it attached.

Have a great day,
Artur

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Re: How did `echo mem > /sys/power/state ` do ?

wangvictor — Thu, 30 Nov 2017 10:16:11 GMT

Artur Petukhov
Is the Soc IPs need the voltage which is from pmic?

I'm not quite sure what is the Soc IPs stand for.