how does CONFIG_PM_AUTOSLEEP work?

[xlin]

Hi,

I am running Linux3.10.17 on imx6sl evk. I am trying to put imx6sl evk into a low power mode when the system become idle. when configuring the kernel, I enabled the following PM related options-

CONFIG_SUSPEND=y

CONFIG_SUSPEND_FREEZER=y

CONFIG_PM_SLEEP=y

CONFIG_PM_SLEEP_SMP=y

CONFIG_PM_AUTOSLEEP=y

I understand that Freescale provides unit tests for PM functions by "echo xxxx > /sys/power/state". But I need something working automatically, which I think "CONFIG_PM_AUTOSLEEP=y" sounds like does, but it seems  doing nothing. Do I need extra steps to enable auto-sleep mode on Linux3.10.17?

Thanks,

Xinsi Lin

[KursadOney]

Xinsi,

This article might help: https://lwn.net/Articles/479841/

Also this one: https://events.linuxfoundation.org/images/stories/pdf/lcna_co2012_wysocki.pdf

Usually the kernel facilities provide the mechanism and the policy is left to the user space. The user space can keep track of the activity level and decide to put the system to sleep when it deems justified. The autosleep feature was ported over from Android (and as far as I know, not used very often elsewhere) and relies on a kernel heuristic and the setup to do power management decisions. This will still require the user space to configure wakeup sources and suspend blockers properly.

I believe we test PM_SLEEP and some of the modules have PM_RUNTIME_SLEEP support but I don't think we test PM_AUTOSLEEP, So I cannot guarantee how well it'll work with i.mx6. Please remember that only the "mem" and "standby" states are supported by i.mx6.

[xlin]

Thanks, Kursad, for your helpful pointers.

[gusarambula]

On the i.MX6 side I would just like to add to Kursad's answer (which was very clear) that you may also want to look at the information on the BSP Linux Low-level Power Management Driver contained on chapter 16 of the i.MX 6Dual/6Quad Linux Reference Manual, available as part of the BSP document bundle.