linux-kernel - Re: [PATCH RFC 05/22] ACPI: Move ACPI_HOTPLUG

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Date:   Mon, 13 Nov 2023 20:01:27 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, linux-csky@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-parisc@...r.kernel.org, Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com,
        James Morse <james.morse@....com>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Subject: Re: [PATCH RFC 05/22] ACPI: Move ACPI_HOTPLUG_CPU to be disabled on
 arm64 and riscv


On 11/13/23 18:56, Russell King (Oracle) wrote:
> On Mon, Nov 13, 2023 at 10:29:39AM +1000, Gavin Shan wrote:
>> On 11/7/23 20:29, Russell King (Oracle) wrote:
>>> From: James Morse <james.morse@....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@....com>
>>> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
>>> ---
>>> Changes since RFC:
>>>    * Expanded conditions to avoid ACPI_HOTPLUG_CPU being enabled when
>>>      HOTPLUG_CPU isn't.
>>> Changes since RFC v3:
>>>    * Dropped ia64 changes
>>> ---
>>>    arch/loongarch/Kconfig        |  1 +
>>>    arch/x86/Kconfig              |  1 +
>>>    drivers/acpi/Kconfig          |  1 -
>>>    drivers/acpi/acpi_processor.c | 18 ------------------
>>>    4 files changed, 2 insertions(+), 19 deletions(-)
>>>
>>
>> With the following nits addressed:
>>
>> Reviewed-by: Gavin Shan <gshan@...hat.com>
>>
>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>>> index d889a0b97bc1..64620e90c12c 100644
>>> --- a/arch/loongarch/Kconfig
>>> +++ b/arch/loongarch/Kconfig
>>> @@ -5,6 +5,7 @@ config LOONGARCH
>>>    	select ACPI
>>>    	select ACPI_GENERIC_GSI if ACPI
>>>    	select ACPI_MCFG if ACPI
>>> +	select ACPI_HOTPLUG_CPU if ACPI_PROCESSOR && HOTPLUG_CPU
>>>    	select ACPI_PPTT if ACPI
>>>    	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
>>>    	select ARCH_BINFMT_ELF_STATE
>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>> index 3762f41bb092..dbdcfc708369 100644
>>> --- a/arch/x86/Kconfig
>>> +++ b/arch/x86/Kconfig
>>> @@ -59,6 +59,7 @@ config X86
>>>    	#
>>>    	select ACPI_LEGACY_TABLES_LOOKUP	if ACPI
>>>    	select ACPI_SYSTEM_POWER_STATES_SUPPORT	if ACPI
>>> +	select ACPI_HOTPLUG_CPU			if ACPI_PROCESSOR && HOTPLUG_CPU
>>>    	select ARCH_32BIT_OFF_T			if X86_32
>>>    	select ARCH_CLOCKSOURCE_INIT
>>>    	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
>>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>>> index f819e760ff19..a3acfc750fce 100644
>>> --- a/drivers/acpi/Kconfig
>>> +++ b/drivers/acpi/Kconfig
>>> @@ -310,7 +310,6 @@ config ACPI_HOTPLUG_CPU
>>>    	bool
>>>    	depends on ACPI_PROCESSOR && HOTPLUG_CPU
>>>    	select ACPI_CONTAINER
>>> -	default y
>>>    config ACPI_PROCESSOR_AGGREGATOR
>>>    	tristate "Processor Aggregator"
>>> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
>>> index 0f5218e361df..4fe2ef54088c 100644
>>> --- a/drivers/acpi/acpi_processor.c
>>> +++ b/drivers/acpi/acpi_processor.c
>>> @@ -184,24 +184,6 @@ static void __init acpi_pcc_cpufreq_init(void) {}
>>>    /* Initialization */
>>>    #ifdef CONFIG_ACPI_HOTPLUG_CPU
>>> -int __weak acpi_map_cpu(acpi_handle handle,
>>> -		phys_cpuid_t physid, u32 acpi_id, int *pcpu)
>>> -{
>>> -	return -ENODEV;
>>> -}
>>> -
>>> -int __weak acpi_unmap_cpu(int cpu)
>>> -{
>>> -	return -ENODEV;
>>> -}
>>> -
>>> -int __weak arch_register_cpu(int cpu)
>>> -{
>>> -	return -ENODEV;
>>> -}
>>> -
>>> -void __weak arch_unregister_cpu(int cpu) {}
>>> -
>>
>> Since we're here, EXPORT_SYMBOL() can be dropped for these functions on
>> x86 and loongarch because they're not called from a module?
> 
> I'm confused, and don't understand your comment. You've r-b the
> previous two patches that remove the EXPORT_SYMBOL()s for
> arch_register_cpu() and arch_unregister_cpu() from x86 and loongarch.
> So it seems your comment is already addressed, and thus makes no
> sense.
> 
> Please clarify.
> 

Exactly, I must be looking into wrong code when reviewing this patch.
Please ignore my comments and my r-b still valid. Sorry for the
unnecessary confusion.

Thanks,
Gavin