Oliver Neukum wrote:
Doubtlessly the ACPI spec is a standard. ... The kernel is very close to this standard. ...
Nothing I've said is incompatible with ACPI models, including the USB portions of the ACPI 2.0 spec. It explicitly allows "full initialization and load" as the "restore" method after D3 (power off) states, and that's what Linux does today with USB after power off: disconnect() all, then enumerate.
Earlier I should have said that D2 is the ACPI-friendly name of the USB suspend state: power reduced, not power off. And also I think D3cold is a PCI-specific state... it's not in ACPI 2.0.
the spec mentions. It specifies the state transitions. It does not specify the _meaning_ of these states. Power management by switching off power has no place in such a spec unless nvram is featured.
Existence and use of any persistent memory is application/device specific. I'd expect the policies for dealing with it to live in userspace, or at least be driven from there.
Would you say "suspend-to-disk" is an ACPI G2 or G3 mode? G2 makes the most sense even though it needs bending to accomodate USB, where disassembly is most certainly safe.
- Dave
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