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Date:   Thu, 30 Nov 2023 16:49:27 +0000
From:   Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To:     Russell King <rmk+kernel@armlinux.org.uk>
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Subject: Re: [PATCH 05/21] ACPI: Move ACPI_HOTPLUG_CPU to be disabled on
 arm64 and riscv
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        <E1r5R31-00Csyt-Jq@rmk-PC.armlinux.org.uk>
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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>