Uploaded August 2025 | Updated September 2026, 2 hours ago
One of the main things still missing in FreeBSD for it to be usable on modern laptops is the ability to go to sleep. In the past, this was done using ACPI S3, but newer laptops have removed this in favour of S0ix, leaving FreeBSD without support for suspend on those machines.
This talk aims to get the casual user familiar enough with the terms and concepts behind power management, such that they can understand what's going on, what's already possible, what can be done, and be able to narrow down power management issues they might encounter.
Full description
This talk will cover:
The background and history of power management on FreeBSD, from APM, to ACPI S3, and finally to s2idle/S0ix, and how to know whether or not a given laptop supports S3 or S0ix or both.
What the full suspend process looks like with modern standby, going into details like ACPI D-states & power resources, SPMC DSMs (acpi_spmc), the AMD SMU (system management unit, amdsmu), etc. and some of the challenges encountered.
Specifics about sleep on AMD, such as USB4 power management in the HCM (host connection manager) and GPIO controller interrupt servicing.
Cover debugging with residency counters, with the SMU on AMD, _LPI objects, and LPIT on Intel.
Niceties and potential future work, such as idleness determination, a powertop equivalent, a built in amd_s2idle.py equivalent (for debugging sleep issues), etc.
One of the main things still missing in FreeBSD for it to be usable on modern laptops is the ability to go to sleep. In the past, this was done using ACPI S3, but newer laptops have removed this in favour of S0ix, leaving FreeBSD without support for suspend on those machines.
This talk aims to get the casual user familiar enough with the terms and concepts behind power management, such that they can understand what's going on, what's already possible, what can be done, and be able to narrow down power management issues they might encounter.
Full description
This talk will cover:
The background and history of power management on FreeBSD, from APM, to ACPI S3, and finally to s2idle/S0ix, and how to know whether or not a given laptop supports S3 or S0ix or both.
What the full suspend process looks like with modern standby, going into details like ACPI D-states & power resources, SPMC DSMs (acpi_spmc), the AMD SMU (system management unit, amdsmu), etc. and some of the challenges encountered.
Specifics about sleep on AMD, such as USB4 power management in the HCM (host connection manager) and GPIO controller interrupt servicing.
Cover debugging with residency counters, with the SMU on AMD, _LPI objects, and LPIT on Intel.
Niceties and potential future work, such as idleness determination, a powertop equivalent, a built in amd_s2idle.py equivalent (for debugging sleep issues), etc.
