Re: [PATCH RFC 05/22] ACPI: Move ACPI_HOTPLUG_CPU to be disabled on arm64 and riscv

[Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>]

On Tue, 07 Nov 2023 10:29:44 +0000
Russell King <rmk+kernel@xxxxxxxxxxxxxxx> wrote:

> From: James Morse <james.morse@xxxxxxx>
> 
> 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@xxxxxxx>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>