Power saving and screen locking in Sway

Pre-requirements

To enable power saving rules described in this post, you need to install these tools:

• swayidle - IDLE management daemon
• swaylock or swaylock-effects - screen locking utility for Wayland compositors
• ddcutil - program for managing monitor settings, such as brightness, color levels, and input source through DDC/CI (Display Data Channel Command Interface)
• power-profiles-daemon
  • Makes power profiles handling available over D-Bus
• cpupower - shows and sets processor power related values

Rules

The goal is to implement power saving rules for IDLE state:

• after 2 minutes: lower the brightness of the LCD
• after 4 minutes: lock the screen
• after 5 minutes: turn off LCD displays (turn off DPMS)
• after 30 minutes: suspend operating system

Final configuration

Add these lines to Sway’s config file:

exec_always killall -9 swayidle && swayidle -w \
  timeout 120  'ddcutil detect | awk "/Display/ {print \$2}" | xargs -I{} ddcutil setvcp 10 30 --display {}' \
  resume        'ddcutil detect | awk "/Display/ {print \$2}" | xargs -I{} ddcutil setvcp 10 100 --display {}' \
  timeout 240  'swaylock -f --fade-in 5 --grace 10' \
  timeout 300  'swaymsg "output * dpms off"' \
  resume      'swaymsg "output * dpms on"' \
  timeout 1800 'systemctl suspend' \
  before-sleep 'swaylock -f'

CPU powersaving

1. Enable power-profiles-daemon

   systemctl enable --now power-profiles-daemon
   

2. Activate power profile:

   powerprofilesctl set power-saver
   

   (instead of power-saver profile you can use other one; check what profiles are available by executing powerprofilesctl without arguments)

How it works

Control LCD through DDC/CI

Modern LCDs have DDC Command Interface implemented.

First, you should detect your displays:

ddcutil detect

Then you can inspect capabilities of DDC, for example:

ddcutil capabilities  --display 1

For example, my Dell U2417H returns these capabilities:

Model: U2417H
MCCS version: 2.1
Commands:
   Op Code: 01 (VCP Request)
   Op Code: 02 (VCP Response)
   Op Code: 03 (VCP Set)
   Op Code: 07 (Timing Request)
   Op Code: 0C (Save Settings)
   Op Code: E3 (Capabilities Reply)
   Op Code: F3 (Capabilities Request)
VCP Features:
   Feature: 02 (New control value)
   Feature: 04 (Restore factory defaults)
   Feature: 05 (Restore factory brightness/contrast defaults)
   Feature: 08 (Restore color defaults)
   Feature: 10 (Brightness)
   Feature: 12 (Contrast)
   Feature: 14 (Select color preset)
      Values:
         01: sRGB
         04: 5000 K
         05: 6500 K
         06: 7500 K
         08: 9300 K
         09: 10000 K
         0b: User 1
         0c: User 2
   Feature: 16 (Video gain: Red)
   Feature: 18 (Video gain: Green)
   Feature: 1A (Video gain: Blue)
   Feature: 60 (Input Source)
      Values:
         10: DisplayPort-2
         0f: DisplayPort-1
         11: HDMI-1
   Feature: AA (Screen Orientation)
      Values:
         01: 0 degrees
         02: 90 degrees
         03: 180 degrees
         04: 270 degrees
   Feature: AC (Horizontal frequency)
   Feature: AE (Vertical frequency)
   Feature: B6 (Display technology type)
   Feature: C6 (Application enable key)
   Feature: C8 (Display controller type)
   Feature: C9 (Display firmware level)
   Feature: D6 (Power mode)
      Values:
         01: DPM: On,  DPMS: Off
         04: DPM: Off, DPMS: Off
         05: Write only value to turn off display
   Feature: DC (Display Mode)
      Values:
         00: Standard/Default mode
         02: Mixed
         03: Movie
         05: Games
   Feature: DF (VCP Version)
   Feature: E0 (Manufacturer specific feature)
   Feature: E1 (Manufacturer specific feature)
   Feature: E2 (Manufacturer specific feature)
      Values: 00 01 02 04 0B 0C 0D 0F 10 11 13 14 19 (interpretation unavailable)
   Feature: F0 (Manufacturer specific feature)
      Values: 08 (interpretation unavailable)
   Feature: F1 (Manufacturer specific feature)
   Feature: F2 (Manufacturer specific feature)
   Feature: FD (Manufacturer specific feature)

We’re looking for VCP 0x10, which in VESA standard is a feature for controlling the Brightness, and we’ll use VCP set command 0x03 to set a new brightness value.

In the example below, the command is setting brightness (VCP 0x10) to 75 for LCD #1:

ddcutil setvcp 10 75 --display 1

When setting up timeout command for swayidle, remember to add command reversing the state after resume, like:

exec_always swayidle -w \
  timeout 120   'ddcutil setvcp 10 30 --display 1' \
  resume        'ddcutil setvcp 10 100 --display 1'

You can play with any features you want to control for power saving. Read full VESA DDC/CI Specification for more details.

Swaylock

For locking the screen I recommend to use swaylock, or more preferrably – swaylock-effects.

The example config ~/.config/swaylock/config could look like:

screenshots
clock
effect-blur=6x6
effect-vignette=0.5:0.5

color=1e1e2e

indicator-idle-visible
indicator-radius=140
indicator-thickness=12

key-hl-color=89b4fa
bs-hl-color=f38ba8
inside-color=313244
inside-clear-color=313244
inside-ver-color=313244
inside-wrong-color=313244

ring-color=45475a
ring-clear-color=89dceb
ring-ver-color=89b4fa
ring-wrong-color=f38ba8

text-color=cdd6f4
text-clear-color=cdd6f4
text-ver-color=cdd6f4
text-wrong-color=cdd6f4

show-failed-attempts

This configuration will take a screenshot, apply blur and vignette, and display the clock.

By using grace argument, you can set a gap between starting a screen lock (fading and bluring the screen) and requiring the password to unlock the screen. So by calling:

swaylock --grace 10 --fade-in 5

the screen will fade in 5 seconds, and require password after 10 seconds.

Remember to add -f argument (daemonize) when calling in swayidle. Without the -f argument, swayidle will wait until password is enetered!

exec_always swayidle -w \
  timeout 240  'swaylock -f --fade-in 5 --grace 10'

Turning off LCDs

You can turn on or off LCDs by swaymsg. Sway’s output command can control DPMS directly.

For turn off the LCDs you must call:

swaymsg "output * dpms off"

For turn on the LCDs you must call:

swaymsg "output * dpms on"

Apply these commadns as timeout and resume commands of swayidle:

exec_always swayidle -w \
  timeout 300  'swaymsg "output * dpms off"' \
  resume 'swaymsg "output * dpms on"'

AMD CPU freq scaling

For AMD CPUs like Ryzen, you must enable amd_pstate feature in Linux. To do that you must edit /etc/default/grub file and enable the feature in GRUB_CMDLINE_LINUX_DEFAULT line by adding:

amd_pstate=active

The full command line will look like:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash [...] amd_pstate=active"

Then you must update GRUB:

update-grub

Now you must reboot your PC. To verify if amd_pstate is working, you should call in the terminal:

# cat /sys/devices/system/cpu/amd_pstate/status
active

• Linux
• Sway
• Wayland