PowerManagement [FreeBSD WIKI]

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**Session Leader:** bwidawsk

[[https://hackmd.io/VaJFdkU7QWeKSjWO8odNkA|hackmd]] (content has been migrated to this page)

Previous Generation
  * <del>S1</del>
  * <del>S2</del>
  * S3
  * S4 - useful as BIOS reinits all hardware on resume

Opportunistic Idle (Runtime PM)
  * power down USB devices, SATA, etc?
  * We can switch PCI devices without drivers to D3, but this is disabled by default (hw.pci.do_power_nodriver=0) as it breaks things

Next Generation
  * Intel's Low Power Idle (s0i1, s0i3 - aka s0ix)
    * Some systems going forward just don't support S3
    * S3 Emulation (Linux "suspend to idle")
    * Opportunistic Idle
    * https://www.uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf

turbostat is in ports, replacement for powertop

Known S3 Issues
  * LCD on various laptops (often KMS fixes this)
  * nvidia(4)
  * em(4) on some systems does not survive resume (Thinkpad X220)
  * Some Samsung nvd(4) drives will need nvme(4) code to suspend/resume successfully
  * Some devices have broken timecounters on resume (either frozen, or racing)
  * S4 may be useful as a base suspend/resume when S3 doesn't work