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System76 Power Management

system76-power is a utility for managing graphics and power profiles.

Switchable Graphics

Switchable graphics is a feature for laptops and all-in-one PCs. It is not supported on desktops.

A reboot is required for changes to take effect after switching modes.

Integrated

The integrated graphics controller on the Intel or AMD CPU is used exclusively.

Lower graphical performance with a longer battery life.

External displays connected to the dGPU ports cannot be used.

NVIDIA

The dGPU (NVIDIA) is used exclusively.

Higher graphical performance at the expense of a shorter battery life.

Allows using external displays.

Hybrid

Enables PRIME render offloading. The iGPU is used as the primary renderer, with the ability to have specific applications render using the dGPU.

PRIME render offloading requires the 435.17 NVIDIA drivers or later.

Applications must use GLVND to take advantage of this feature, so may not render on the dGPU even when requested. Vulkan applications must be launched with __NV_PRIME_RENDER_OFFLOAD=1 to render on the dGPU. GLX applications must be launched with __NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia to render on the dGPU.

Display offload sinks ("reverse PRIME") require 450.57 NVIDIA drivers or later. This feature allows using external displays while in this mode.

GPU support for run-time power management is required for the device to enter a low power state when not used. Only Turing cards and newer fully implement this functionality. Support for run-time power manage can be checked in the supported-gpus.json file provided by the driver. e.g.:

$ cat /sys/bus/pci/devices/0000:01:00.0/device
0x1f15
$ jq '.chips[] | select(.devid=="0x1F15")' < /usr/share/doc/nvidia-driver-460/supported-gpus.json
{
  "devid": "0x1F15",
  "name": "GeForce RTX 2060",
  "features": [
    "dpycbcr420",
    "dpgsynccompatible",
    "hdmi4k60rgb444",
    "hdmigsynccompatible",
    "geforce",
    "runtimepm",
    "vdpaufeaturesetJ"
  ]
}

Compute

The integrated graphics controller is used exclusively for rendering. The dGPU is made available as a compute node.

Power Profiles

Balanced

• Set the sync data to disk to 15s
• Enables laptop mode feature in kernel
• Enables SCSI/SATA link time power management
• Controls the Intel PState values if they exist

Performance

• Uses settings from Balanced
• Uses ACPI Platform profile if the hardware is supported by the kernel

Battery

• Uses settings from Performance
• Sets Screen brightness to a lower value
• Turns keyboard backlight off

Hotplug detection

The dbus signal HotPlugDetect is sent when a display is plugged into a port connected to the dGPU. If in integrated or compute mode, the GNOME extension will prompt to switch to hybrid mode so the display can be used.

Adding hotplug detection

Intel-based systems

The GPIO (sideband) port and pins for the display ports can be determined with the schematics and output of coreboot-collector. The schematics will indicate which GPIOs are display ports (*_HPD). The corresponding GPP_* entry in coreboot-collector.txt will have the port/pin tuple.

Muxed DisplayPort

Some models have muxed DisplayPort ouput from mDP and USB-C. These units have a separate data switch pin that is used to determine which output is used.

AMD-based systems

A MMIO region for FCH GPIO controls is used to detect external display plug events. Display ports use *_HPD as Intel systems, but may not map to a literal GPIO (e.g., HDMI_HPD maps to DP3_HPD on kudu6). Generating a diff from coreboot-collector in NVIDIA mode before and after plugging in a display should provide the GPIO number.