radeontool

Turn off the laptop backlight

$ radeontool light off

$ radeontool light on

$ radeontool dac off

$ radeontool dac on

$ radeontool regs

$ radeontool regmatch [pattern]

$ radeontool regset [pattern] [value]

radeontool [options] [command]

radeontool is a utility for controlling hardware features on ATI Radeon-based graphics cards, primarily used on laptops. It provides direct access to backlight control, external display output, and low-level register manipulation.
The tool communicates directly with the graphics hardware through memory-mapped I/O, allowing control over features not exposed through standard display drivers. Common uses include scripted backlight control for power management and debugging display issues.

light [on|off]

Control the laptop panel backlight power state

Control external video output (VGA/DVI) power state

Control LCD stretching when running non-native resolutions

Display a sampling of important register values

Show registers whose names match the wildcard pattern

Set registers matching the wildcard pattern to value

Enable verbose debugging output

Skip the first n Radeon cards and operate on card n+1

Root privileges required for most operations due to direct hardware access via /dev/mem.
Register manipulation is dangerous: Using regset incorrectly can cause system instability or permanent hardware damage. Only modify registers if you understand the consequences.
Not all features work on all cards: Compatibility varies between Radeon generations. Test commands carefully on your specific hardware.

radeontool was created by David Airlie as part of the Linux open-source graphics effort. It emerged in the early 2000s when ATI Radeon cards required userspace tools to control features not yet supported by the kernel drivers.

xrandr(1), xbacklight(1), aticonfig(1)