RE: S4 hibernate design document

obiwac <obiwac_at_freebsd.org> wrote on
Date: Thu, 16 Oct 2025 14:19:43 UTC :

> Hi again!
> 
> Following up on the previous email announcing the Foundation's intent to add S4
> hibernate support to FreeBSD [1], kib@ has started working on a more detailed
> design document for this:
> 
> https://hackmd.io/@eJNIw-SNShyq1LSp2azAcw/Bka-kXTpge
> 
> There are still a couple unsolved bits of the design, so we'd like to gather
> some more feedback on this document. If you could reply with any feedback
> within a week (before Oct 23rd) that would be ideal for us!
> 
> Thanks,
> Aymeric on behalf of the FreeBSD Foundation
> 
> [1] https://lists.freebsd.org/archives/freebsd-current/2025-August/008616.html

I'm not sure how it fits with the material referenced above, but I'll
note that ACPI references S4 handling in at least the following,
including some of the _OSC usage that is tied to USB4 handling . . .


6.2.11. _OSC (Operating System Capabilities)

. . .

Since platorm context is lost when the platorm enters the S4 sleeping state, OSPM
must re-evaluate _OSC upon wake from S4 to restore the previous platorm state.
This requirement will vary depending on the device specific _OSC func!onality.

. . .

6.2.11.1.2. Evaluation Conditions

. . .

Upon resume from S4. Platorm firmware will handle context restora!on when
resuming from S1-S3.

. . .

6.2.11.3. Operating System Capabilities (_OSC) for USB

. . .

Note: OSPM must re-invoke _OSC during S4 resume.

. . .

6.3. Device Insertion, Removal, and Status Objects

. . .

For removing devices, ACPI supports both hot removal (system is in the S0 state),
and warm removal (system is in a sleep state: S1-S4). This is done using the _EJx
control methods. Devices that can be ejected include an _EJx control method for
each sleeping state the device supports (a maximum of 2 _EJx objects can be listed).
For example, hot removal devices would supply an _EJ0; warm removal devices
would use one of _EJ1-EJ4. These control methods are used to signal the hardware
when an eject is to occur.

The sequence of events for dynamically removing a device goes as follows:

. . .


===
Mark Millard
marklmi at yahoo.com