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https://github.com/pop-os/system76-power

System76 Power Management
https://github.com/pop-os/system76-power

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System76 Power Management

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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"

  ]

}

```



[GLVND]: https://gitlab.freedesktop.org/glvnd/libglvnd



### 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.



[GNOME extension]: https://github.com/pop-os/gnome-shell-extension-system76-power



### 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.



[coreboot-collector]: https://github.com/system76/coreboot-collector