linux-kernel - Re: [PATCH] LoongArch: Give chance to build under !CONFIG

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Date: Wed, 27 Mar 2024 05:30:58 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: maobibo <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Arnd Bergmann <arnd@...db.de>,
 Marc Zyngier <maz@...nel.org>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
 loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Give chance to build under !CONFIG_SMP

Hi Bibo,

On 3/26/24 20:58, maobibo wrote:
> 
> 
> On 2024/3/26 下午2:21, Tiezhu Yang wrote:
>> In the current code, SMP is selected in Kconfig for LoongArch, the users
>> can not unset it, this is reasonable for a multiprocessor machine. But as
>> the help info of config SMP said, if you have a system with only one CPU,
>> say N. On a uniprocessor machine, the kernel will run faster if you say N
>> here.
>>
>> The Loongson-2K0500 is a single-core CPU for applications like industrial
>> control, printing terminals, and BMC (Baseboard Management Controller),
>> there are many development boards, products and solutions on the market,
>> so it is better and necessary to give a chance to build under !CONFIG_SMP
>> for a uniprocessor machine.

..

>> +++ b/arch/loongarch/include/asm/smp.h
>> @@ -6,6 +6,7 @@
>>   #ifndef __ASM_SMP_H
>>   #define __ASM_SMP_H
>> +#ifdef CONFIG_SMP
>>   #include <linux/atomic.h>
>>   #include <linux/bitops.h>
>>   #include <linux/linkage.h>
>> @@ -101,4 +102,8 @@ static inline void __cpu_die(unsigned int cpu)
>>   }
>>   #endif
>> +#else /* !CONFIG_SMP */
>> +#define cpu_logical_map(cpu)    0
> It is unsafe here though physical cpuid of BSP is 0 always.
> It is better to use __cpu_logical_map[cpu] or read_csr_cpuid()
> 
>> +#endif

..

>> +++ b/arch/loongarch/power/suspend.c
>> @@ -44,7 +44,9 @@ void loongarch_common_resume(void)
>>   {
>>       sync_counter();
>>       local_flush_tlb_all();
>> +#ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
>>       csr_write64(per_cpu_offset(0), PERCPU_BASE_KS);
>> +#endif
> It is another issue, CONFIG_HAVE_SETUP_PER_CPU_AREA should not depend on 
> NUMA. PERCPU_BASE_KS should be set even for UP.

Thanks for your review and suggestions.

Let me wait for some days, if no more comments, I will address in v3 
since the v2 has been sent.

Thanks,
Tiezhu