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docs: Update CSME note about S0ix/TGL-U

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CSME should be enabled when S0ix is used for power savings during
suspend. TGL-U is just one case where we default as our TGL-U models
do not support S3. Other models may use S0ix as well, such as darp8 and
darp9 due to new batches just not working with S3 anymore [1].

[1]: https://github.com/system76/firmware-open/issues/507

Signed-off-by: Tim Crawford <tcrawford@system76.com>
This commit is contained in:
Tim Crawford
2024-03-01 11:40:37 -07:00
committed by Jeremy Soller
parent 120c2fd271
commit 7a60055f68
1 changed files with 11 additions and 8 deletions
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19
docs/intel-me.md
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@@ -55,15 +55,18 @@ ME: Current Operation Mode : 0
ME: Error Code : 0
```
## Tiger Lake-U
## S0ix
Models using TGL-U processors default to having the IME enabled. TGL-U removes
support for S3 and requires S0ix. This requires all CPU, PCH, and PCIe devices
to have ACPI defined low power states. With S0ix, the CPU has numerous states
for low power, with the lowest being C10. In order to reach this C10 state, the
IME must report that it is in a low power state. Disabling the ME with the HAP
bit keeps the CPU in the C8 state. This nearly triples the power usage in S0ix
suspend, from around 1 watt to around 3 watts.
S0ix (Modern Standby, s2idle) requires all CPU, PCH, and PCIe devices to have
ACPI defined low power states. The CPU has numerous states for low power, with
the lowest being C10. In order to reach this C10 state, the CSME must report
that it is in a low power state.
Disabling the CSME with the HAP bit or HECI command keeps the CPU in the C8
state. This nearly triples the power usage in S0ix suspend, from around 1 watt
to around 3 watts.
TGL-U removed support for S3 and requires S0ix.
[wiki]: https://en.wikipedia.org/wiki/Intel_Management_Engine