This series is a backport of the ACPI PPTT 6.3 thread flag feature for supporting arm64 systems.
The background is that some arm64 implementations are broken, in that they incorrectly advertise that a CPU is mutli-threaded, when it is not - the HiSilicon Taishanv110 rev 2, aka tsv110, being an example.
This leads to the system topology being incorrect. The reason being that arm64 topology code uses a combination of ACPI PPTT (Processor Properties Topology Table) and the system MPIDR (Multiprocessor Affinity Register) MT bit to determine the topology.
Until ACPI 6.3, the PPTT did not have any method to determine whether a CPU was multi-threaded, so only the MT bit is used - hence the broken topology for some systems.
In ACPI 6.3, a PPTT thread flag was introduced, which - when supported - would be used by the kernel to determine really if a CPU is multi-threaded or not, so that we don't get incorrect topology.
RFC originally sent for 4.19: https://lkml.org/lkml/2019/10/10/724 Jeremy Linton (2): ACPI/PPTT: Add support for ACPI 6.3 thread flag arm64: topology: Use PPTT to determine if PE is a thread
arch/arm64/kernel/topology.c | 19 ++++++++++--- drivers/acpi/pptt.c | 52 ++++++++++++++++++++++++++++++++++++ include/linux/acpi.h | 5 ++++ 3 files changed, 72 insertions(+), 4 deletions(-)