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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>
75 lines
2.3 KiB
Markdown
75 lines
2.3 KiB
Markdown
# Intel Management Engine
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[Intel Management Engine][wiki] is a proprietary, mostly undocumented, firmware
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system that provides many extraneous features that are generally not usable or
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useful to our users, with multiple known vulnerabilities that compromise the
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entire system.
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The Intel ME is _required_ (since Nehalem, 2008), so cannot be removed. The
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[me\_cleaner] project is able to remove non-essential components, but does not
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support the ME version used on many of our systems. Instead, we [send a HECI
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command][CB52800] to tell the Intel ME to disable runtime components during
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early boot.
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Most Intel-based machines from System76 come with the IME disabled.
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## Configuring
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The IME can be enabled or disabled via the coreboot CMOS option `me_state`.
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The value can be set using coreboot's nvramtool.
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```
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make -C coreboot/util/nvramtool
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sudo ./coreboot/util/nvramtool/nvramtool -w me_state={Enable,Disable}
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```
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A restart is required for the change to take effect. On the boot after changing
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the value, the system will perform a global reset (power off again) to complete
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the change and ensure the IME is operating in a valid state.
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### Checking the state
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coreboot will log some IME data to cbmem during startup. This can be used to
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check if it is in the correct state.
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```
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make -C coreboot/util/cbmem
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sudo ./coreboot/util/cbmem/cbmem -c
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```
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When disabled it will report:
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```
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ME: Current Working State : 4
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ME: Current Operation State : 1
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ME: Current Operation Mode : 3
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ME: Error Code : 2
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```
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When enabled it will report:
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```
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ME: Current Working State : 5
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ME: Current Operation State : 1
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ME: Current Operation Mode : 0
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ME: Error Code : 0
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```
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## S0ix
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S0ix (Modern Standby, s2idle) requires all CPU, PCH, and PCIe devices to have
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ACPI defined low power states. The CPU has numerous states for low power, with
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the lowest being C10. In order to reach this C10 state, the CSME must report
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that it is in a low power state.
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Disabling the CSME with the HAP bit or HECI command keeps the CPU in the C8
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state. This nearly triples the power usage in S0ix suspend, from around 1 watt
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to around 3 watts.
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TGL-U removed support for S3 and requires S0ix.
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[wiki]: https://en.wikipedia.org/wiki/Intel_Management_Engine
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[me\_cleaner]: https://github.com/corna/me_cleaner
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[CB52800]: https://review.coreboot.org/c/coreboot/+/52800
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