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Content-Language: en-US To: Jonathan Cameron , Thomas Gleixner , Peter Zijlstra , linux-pm@vger.kernel.org, loongarch@lists.linux.dev, linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, x86@kernel.org, Russell King , "Rafael J . Wysocki" , Miguel Luis , James Morse , Salil Mehta , Jean-Philippe Brucker , Catalin Marinas , Will Deacon , Marc Zyngier , Hanjun Guo Cc: Ingo Molnar , Borislav Petkov , Dave Hansen , linuxarm@huawei.com, justin.he@arm.com, jianyong.wu@arm.com, Lorenzo Pieralisi , Sudeep Holla References: <20240426135126.12802-1-Jonathan.Cameron@huawei.com> <20240426135126.12802-14-Jonathan.Cameron@huawei.com> From: Gavin Shan In-Reply-To: <20240426135126.12802-14-Jonathan.Cameron@huawei.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/26/24 23:51, Jonathan Cameron wrote: > The ARM64 architecture does not support physical CPU HP today. > To avoid any possibility of a bug against such an architecture if defined > in future, check for the physical CPU HP case (not present) and > return an error on any such attempt. > > On ARM64 virtual CPU Hotplug relies on the status value that can be > queried via the AML method _STA for the CPU object. > > There are two conditions in which the CPU can be registered. > 1) ACPI disabled. > 2) ACPI enabled and the acpi_handle is available. > _STA evaluates to the CPU is both enabled and present. > (Note that in absence of the _STA method they are always in this > state). > > If neither of these conditions is met the CPU is not 'yet' ready > to be used and -EPROBE_DEFER is returned. > > Success occurs in the early attempt to register the CPUs if we > are booting with DT (no concept yet of vCPU HP) if not it succeeds > for already enabled CPUs when the ACPI Processor driver attaches to > them. Finally it may succeed via the CPU Hotplug code indicating that > the CPU is now enabled. > > For ACPI if CONFIG_ACPI_PROCESSOR the only path to get to > arch_register_cpu() with that handle set is via > acpi_processor_hot_add_init() which is only called from an ACPI bus > scan in which _STA has already been queried there is no need to > repeat it here. Add a comment to remind us of this in the future. > > Suggested-by: Rafael J. Wysocki > Tested-by: Miguel Luis > Signed-off-by: Jonathan Cameron > --- > V8: No change. (tags collected only) > --- > arch/arm64/kernel/smp.c | 53 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 53 insertions(+) > Reviewed-by: Gavin Shan