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SubjectRe: [PATCH] MIPS: No need to check CPU 0 in {loongson3,bmips,octeon}_cpu_disable()
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On 12/15/2020 11:26 AM, liwei (GF) wrote:
> 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?

The early discussion is here:
https://patchwork.kernel.org/project/linux-mips/patch/1594896024-16624-1-git-send-email-chenhc@lemote.com/

As Jiaxun said, it seems that this is a software limitation.
I think the initial aim of commit 9cce844abf07 ("MIPS: CPU#0 is not
hotpluggable")
is to solve ltp test failure.

>
>> c->hotpluggable is 0 for CPU 0 and it will not generate a control
>> file in sysfs for this CPU:
>>
>> [root@linux loongson]# cat /sys/devices/system/cpu/cpu0/online
>> cat: /sys/devices/system/cpu/cpu0/online: No such file or directory
>> [root@linux 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()?

Yes, thank you, let me send a patch to do it.

Thanks,
Tiezhu

>
> Thanks,
> Wei
>
>> just remove them.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.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);
>>

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