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    SubjectRe: [PATCH 05/21] ACPI: Move ACPI_HOTPLUG_CPU to be disabled on arm64 and riscv
    On Tue, 21 Nov 2023 13:44:15 +0000
    Russell King <rmk+kernel@armlinux.org.uk> wrote:

    > From: James Morse <james.morse@arm.com>
    >
    > Neither arm64 nor riscv support physical hotadd of CPUs that were not
    > present at boot. For arm64 much of the platform description is in static
    > tables which do not have update methods. arm64 does support HOTPLUG_CPU,
    > which is backed by a firmware interface to turn CPUs on and off.
    >
    > acpi_processor_hotadd_init() and acpi_processor_remove() are for adding
    > and removing CPUs that were not present at boot. arm64 systems that do this
    > are not supported as there is currently insufficient information in the
    > platform description. (e.g. did the GICR get removed too?)
    >
    > arm64 currently relies on the MADT enabled flag check in map_gicc_mpidr()
    > to prevent CPUs that were not described as present at boot from being
    > added to the system. Similarly, riscv relies on the same check in
    > map_rintc_hartid(). Both architectures also rely on the weak 'always fails'
    > definitions of acpi_map_cpu() and arch_register_cpu().
    >
    > Subsequent changes will redefine ACPI_HOTPLUG_CPU as making possible
    > CPUs present. Neither arm64 nor riscv support this.
    >
    > Disable ACPI_HOTPLUG_CPU for arm64 and riscv by removing 'default y' and
    > selecting it on the other three ACPI architectures. This allows the weak
    > definitions of some symbols to be removed.
    >
    > Signed-off-by: James Morse <james.morse@arm.com>
    > Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
    > Reviewed-by: Gavin Shan <gshan@redhat.com>
    > Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
    Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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