linux-kernel - Re: [PATCH] MIPS: No need to check CPU 0 in {loongson3,bmips,octeon}_cpu

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Date:   Tue, 15 Dec 2020 11:26:59 +0800
From:   "liwei (GF)" <liwei391@...wei.com>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Florian Fainelli <f.fainelli@...il.com>
CC:     <linux-mips@...r.kernel.org>,
        <bcm-kernel-feedback-list@...adcom.com>,
        <linux-kernel@...r.kernel.org>, Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH] MIPS: No need to check CPU 0 in
 {loongson3,bmips,octeon}_cpu_disable()

Hi,

On 2020/11/25 18:11, Tiezhu Yang wrote:
> After commit 9cce844abf07 ("MIPS: CPU#0 is not hotpluggable"),

Why CPU#0 is not hotpluggable on MIPS? Does that unrealizable?

> c->hotpluggable is 0 for CPU 0 and it will not generate a control
> file in sysfs for this CPU:
> 
> [root@...ux loongson]# cat /sys/devices/system/cpu/cpu0/online
> cat: /sys/devices/system/cpu/cpu0/online: No such file or directory
> [root@...ux loongson]# echo 0 > /sys/devices/system/cpu/cpu0/online
> bash: /sys/devices/system/cpu/cpu0/online: Permission denied
> 
> So no need to check CPU 0 in {loongson3,bmips,octeon}_cpu_disable(),

missing cps_cpu_disable()?

Thanks,
Wei

> just remove them.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>  arch/mips/cavium-octeon/smp.c | 3 ---
>  arch/mips/kernel/smp-bmips.c  | 3 ---
>  arch/mips/loongson64/smp.c    | 3 ---
>  3 files changed, 9 deletions(-)
> 
> diff --git a/arch/mips/cavium-octeon/smp.c b/arch/mips/cavium-octeon/smp.c
> index 076db9a..66ce552 100644
> --- a/arch/mips/cavium-octeon/smp.c
> +++ b/arch/mips/cavium-octeon/smp.c
> @@ -290,9 +290,6 @@ static int octeon_cpu_disable(void)
>  {
>  	unsigned int cpu = smp_processor_id();
>  
> -	if (cpu == 0)
> -		return -EBUSY;
> -
>  	if (!octeon_bootloader_entry_addr)
>  		return -ENOTSUPP;
>  
> diff --git a/arch/mips/kernel/smp-bmips.c b/arch/mips/kernel/smp-bmips.c
> index 1dbfb5a..359b176 100644
> --- a/arch/mips/kernel/smp-bmips.c
> +++ b/arch/mips/kernel/smp-bmips.c
> @@ -362,9 +362,6 @@ static int bmips_cpu_disable(void)
>  {
>  	unsigned int cpu = smp_processor_id();
>  
> -	if (cpu == 0)
> -		return -EBUSY;
> -
>  	pr_info("SMP: CPU%d is offline\n", cpu);
>  
>  	set_cpu_online(cpu, false);
> diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
> index aa0cd72..b8c1fc3 100644
> --- a/arch/mips/loongson64/smp.c
> +++ b/arch/mips/loongson64/smp.c
> @@ -544,9 +544,6 @@ static int loongson3_cpu_disable(void)
>  	unsigned long flags;
>  	unsigned int cpu = smp_processor_id();
>  
> -	if (cpu == 0)
> -		return -EBUSY;
> -
>  	set_cpu_online(cpu, false);
>  	calculate_cpu_foreign_map();
>  	local_irq_save(flags);
>