ibm,opal/power-mgt/occ device tree entries

This node exports the per-chip pstate table properties to kernel.

Example:

occ@7ffddf8000 {
       ibm,pstate-vdds = [45 45 46 46 46 47 48 49 4a 4b 4c 4d 4f 50 51 52 53 54 55 57 58 59 5a 5b 5c 5d 5e 5f 5f 60 61 62 63 64 65 65 66 67 68 69 6a 6a 6b 6c 6d 6e 6f 70 70 71];
       ibm,chip-id = <0x1>;
       phandle = <0x100003b8>;
       ibm,pstate-vcss = [3b 3d 3f 41 42 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f 50 50 51 52 53 54 55 56 56 57 57 58 58 59 59 5a 5a 5b 5b 5c 5c 5d 5d 5e 5e 5f 5f 60 60 61 61 62 62];
       reg = <0x7f 0xfddf8000 0xb98>;
};

ibm,chip-id

This property denotes the ID of chip to which OCC belongs to.

reg

This tuple gives the statring address of the OPAL data in HOMER and the size of the OPAL data.

The top-level /ibm,opal/power-mgt contains :

#size-cells = <1>
#address-cells = <2>

ibm,pstate-vcss ibm,pstate-vdds

These properties list a voltage-identifier of each of the pstates listed in ibm,pstate-ids for the Vcs and Vdd values used for that pstate in that chip. Each VID is a single byte.

ibm,opal/power-mgt/freq-domain-mask

This property is a bitmask which will have different value depending upon the generation of the processor. Frequency domain would indicate group of CPUs which would share same frequency. Bitwise AND is taken between this bitmask value and PIR of cpu. All the CPUs lying in the same frequency domain will have same result for AND. Thus frequency management can be done based on frequency domain. A frequency domain may be a core or a quad, etc depending upon the generation of the processor.

For example, for POWER8 0xFFF8 indicates core wide frequency domain. Taking AND with the PIR of CPUs will yield us a frequency domain which is core wide distribution as last 3 bits have been masked which represent the threads.

For POWER9, 0xFFF0 indicates quad wide frequency domain. Taking AND with the PIR of CPUs will yield us frequency domain which is quad wise distribution as last 4 bits have been masked which represent the cores.

ibm,opal/power-mgt/domain-runs-at

There are two strategies in which the OCC can change the frequency of the cores in the quad on P9. 1) FREQ_MAX_IN_DOMAIN : the OCC sets the frequency of the quad to the maximum of the latest frequency requested by each of the component cores. 2) FREQ_MOST_RECENTLY_SET : the OCC sets the frequency of the quad to the most recent frequency value requested by the CPUs in the quad

In case of P8, the domain is the core and the strategy by default is FREQ_MOST_RECENTLY_SET since the PMCRs of the threads in the core are mirrored. However on P9, the domain is quad and the strategy is FREQ_MAX_IN_DOMAIN since each core has its own PMCR.

domain-runs-at denotes the strategy which OCC is using to change the frequency of a frequency domain.