[v2] ACPI/arm64: add support for virtual cpuhotplug

[RFC PATCH v2 25/35] LoongArch: Use the __weak version of arch_unregister_cpu()

Posted by James Morse 2 years, 3 months ago

LoongArch provides its own arch_unregister_cpu(). This clears the
hotpluggable flag, then unregisters the CPU.

It isn't necessary to clear the hotpluggable flag when unregistering
a cpu. unregister_cpu() writes NULL to the percpu cpu_sys_devices
pointer, meaning cpu_is_hotpluggable() will return false, as
get_cpu_device() has returned NULL.

Remove arch_unregister_cpu() and use the __weak version.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/loongarch/kernel/topology.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/arch/loongarch/kernel/topology.c b/arch/loongarch/kernel/topology.c
index 8e4441c1ff39..5a75e2cc0848 100644
--- a/arch/loongarch/kernel/topology.c
+++ b/arch/loongarch/kernel/topology.c
@@ -16,13 +16,4 @@ int arch_register_cpu(int cpu)
 	return register_cpu(c, cpu);
 }
 EXPORT_SYMBOL(arch_register_cpu);
-
-void arch_unregister_cpu(int cpu)
-{
-	struct cpu *c = &per_cpu(cpu_devices, cpu);
-
-	c->hotpluggable = 0;
-	unregister_cpu(c);
-}
-EXPORT_SYMBOL(arch_unregister_cpu);
 #endif
-- 
2.39.2

Re: [RFC PATCH v2 25/35] LoongArch: Use the __weak version of arch_unregister_cpu()

Posted by Gavin Shan 2 years, 3 months ago

On 9/14/23 02:38, James Morse wrote:
> LoongArch provides its own arch_unregister_cpu(). This clears the
> hotpluggable flag, then unregisters the CPU.
> 
> It isn't necessary to clear the hotpluggable flag when unregistering
> a cpu. unregister_cpu() writes NULL to the percpu cpu_sys_devices
> pointer, meaning cpu_is_hotpluggable() will return false, as
> get_cpu_device() has returned NULL.
> 
> Remove arch_unregister_cpu() and use the __weak version.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>   arch/loongarch/kernel/topology.c | 9 ---------
>   1 file changed, 9 deletions(-)
> 
I think arch/x86/kernel/topology.c::arch_unregister_cpu() can be dropped either.

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/loongarch/kernel/topology.c b/arch/loongarch/kernel/topology.c
> index 8e4441c1ff39..5a75e2cc0848 100644
> --- a/arch/loongarch/kernel/topology.c
> +++ b/arch/loongarch/kernel/topology.c
> @@ -16,13 +16,4 @@ int arch_register_cpu(int cpu)
>   	return register_cpu(c, cpu);
>   }
>   EXPORT_SYMBOL(arch_register_cpu);
> -
> -void arch_unregister_cpu(int cpu)
> -{
> -	struct cpu *c = &per_cpu(cpu_devices, cpu);
> -
> -	c->hotpluggable = 0;
> -	unregister_cpu(c);
> -}
> -EXPORT_SYMBOL(arch_unregister_cpu);
>   #endif

Thanks,
Gavin

Re: [RFC PATCH v2 25/35] LoongArch: Use the __weak version of arch_unregister_cpu()

Posted by Jonathan Cameron 2 years, 3 months ago

On Wed, 13 Sep 2023 16:38:13 +0000
James Morse <james.morse@arm.com> wrote:

> LoongArch provides its own arch_unregister_cpu(). This clears the
> hotpluggable flag, then unregisters the CPU.
> 
> It isn't necessary to clear the hotpluggable flag when unregistering
> a cpu. unregister_cpu() writes NULL to the percpu cpu_sys_devices
> pointer, meaning cpu_is_hotpluggable() will return false, as
> get_cpu_device() has returned NULL.

Thought that looked odd earlier but didn't care enough to dig.
Seem unlikely state would persist for an unregistered cpu.
Great to see confirmation.

> 
> Remove arch_unregister_cpu() and use the __weak version.
> 
> Signed-off-by: James Morse <james.morse@arm.com>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>


> ---
>  arch/loongarch/kernel/topology.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/arch/loongarch/kernel/topology.c b/arch/loongarch/kernel/topology.c
> index 8e4441c1ff39..5a75e2cc0848 100644
> --- a/arch/loongarch/kernel/topology.c
> +++ b/arch/loongarch/kernel/topology.c
> @@ -16,13 +16,4 @@ int arch_register_cpu(int cpu)
>  	return register_cpu(c, cpu);
>  }
>  EXPORT_SYMBOL(arch_register_cpu);
> -
> -void arch_unregister_cpu(int cpu)
> -{
> -	struct cpu *c = &per_cpu(cpu_devices, cpu);
> -
> -	c->hotpluggable = 0;
> -	unregister_cpu(c);
> -}
> -EXPORT_SYMBOL(arch_unregister_cpu);
>  #endif

Re: [RFC PATCH v2 25/35] LoongArch: Use the __weak version of arch_unregister_cpu()

Posted by Russell King (Oracle) 2 years, 1 month ago

On Thu, Sep 14, 2023 at 03:41:11PM +0100, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:13 +0000
> James Morse <james.morse@arm.com> wrote:
> 
> > LoongArch provides its own arch_unregister_cpu(). This clears the
> > hotpluggable flag, then unregisters the CPU.
> > 
> > It isn't necessary to clear the hotpluggable flag when unregistering
> > a cpu. unregister_cpu() writes NULL to the percpu cpu_sys_devices
> > pointer, meaning cpu_is_hotpluggable() will return false, as
> > get_cpu_device() has returned NULL.
> 
> Thought that looked odd earlier but didn't care enough to dig.
> Seem unlikely state would persist for an unregistered cpu.
> Great to see confirmation.

Would it make sense to move this immedaitely after "LoongArch: Switch
over to GENERIC_CPU_DEVICES" ?

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