Linux 6.8 To Add Intel Idle Driver Support For Sierra Forest & Grand Ridge

The latest bits of future Intel CPU hardware support being queued for the mainline kernel is adding Intel Idle driver support for the upcoming Sierra Forest and Grand Ridge processors.

Queued this week in the power management subsystem's "linux-next" branch is adding support for Sierra Forest and Grand Ridge to the "intel_idle" driver for merging come Linux 6.8. Sierra Forest is the high core count, all-E-core server processor Intel is set to release in 2024. Grand Ridge is an upcoming Intel Atom SoC that has been rumored to be a 7nm ~24 core processor.

The Intel Idle driver for Linux is responsible for CPU idle time management for dealing with the processor's core and package idle states.

The Sierra Forest support in the Intel Idle driver sums up some of the processor's characteristics:

"Add Sierra Forest SoC C-states, which are C1, C1E, C6S, and C6SP.

Sierra Forest SoC is built with modules, each module includes 4 cores (Crestmont microarchitecture). There is one L2 cache per module, shared between the 4 cores.

There is no core C6 state, but there is C6S state, which has module scope: when all 4 cores request C6S, the entire module (4 cores + L2 cache) enters the low power state.

C6SP state has package scope - when all modules in the package enter C6S, the package enters the power state mode."

And the Intel Grand Ridge SoC support for Intel Idle:

Add Intel Grand Ridge SoC C-states, which are C1, C1E, and C6S.

The Grand Ridge SoC is built with modules, each module includes 4 cores (Crestmont microarchitecture). There is one L2 cache per module, shared between the 4 cores.

There is no core C6 state, but there is C6S state, which has module scope: when all 4 cores request C6S, the entire module (4 cores + L2 cache) enters the low power state.

The Linux 6.8 stable kernel should ship by mid-March which should be before either of these Intel processors reach customers for ensuring proper C-state support.