I think this is the reason for the cap. This is the same in all kernels from 4.19.84 up to 5.5.0-rc2
Edit: Interesting. On 4.19.35 it is still capped, though more information in dmesg
[ 5.745212] cpu cpu0: Linked as a consumer to regulator.5
[ 5.745277] cpu cpu0: Dropping the link to regulator.5
[ 5.745464] cpu cpu0: Linked as a consumer to regulator.5
[ 5.746315] core: _opp_supported_by_regulators: OPP minuV: 1320000 maxuV: 1320000, not supported by regulator
[ 5.746328] cpu cpu0: _opp_add: OPP not supported by regulators (1056000000)
[ 5.746436] core: _opp_supported_by_regulators: OPP minuV: 1320000 maxuV: 1320000, not supported by regulator
[ 5.746443] cpu cpu0: _opp_add: OPP not supported by regulators (1104000000)
[ 5.746569] core: _opp_supported_by_regulators: OPP minuV: 1320000 maxuV: 1320000, not supported by regulator
[ 5.746579] cpu cpu0: _opp_add: OPP not supported by regulators (1152000000)
[ 5.746669] core: _opp_supported_by_regulators: OPP minuV: 1320000 maxuV: 1320000, not supported by regulator
[ 5.746676] cpu cpu0: _opp_add: OPP not supported by regulators (1200000000)
[ 5.746783] core: _opp_supported_by_regulators: OPP minuV: 1340000 maxuV: 1340000, not supported by regulator
[ 5.746790] cpu cpu0: _opp_add: OPP not supported by regulators (1224000000)
[ 5.746926] core: _opp_supported_by_regulators: OPP minuV: 1340000 maxuV: 1340000, not supported by regulator
[ 5.746935] cpu cpu0: _opp_add: OPP not supported by regulators (1248000000)
[ 5.747030] core: _opp_supported_by_regulators: OPP minuV: 1340000 maxuV: 1340000, not supported by regulator
[ 5.747038] cpu cpu0: _opp_add: OPP not supported by regulators (1296000000)
[ 5.747155] core: _opp_supported_by_regulators: OPP minuV: 1400000 maxuV: 1400000, not supported by regulator
[ 5.747163] cpu cpu0: _opp_add: OPP not supported by regulators (1344000000)
[ 5.747290] core: _opp_supported_by_regulators: OPP minuV: 1400000 maxuV: 1400000, not supported by regulator
[ 5.747299] cpu cpu0: _opp_add: OPP not supported by regulators (1368000000)
