linux-kernel - Re: [RFC PATCH 5/5] RISC-V: Support cpu hotplug.

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Date:   Tue, 21 Aug 2018 13:23:18 -0700
From:   Atish Patra <atish.patra@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "palmer@...ive.com" <palmer@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "anup@...infault.org" <anup@...infault.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        Damien Le Moal <Damien.LeMoal@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 5/5] RISC-V: Support cpu hotplug.

On 8/21/18 12:55 AM, Christoph Hellwig wrote:
>>   	if (!err) {
>> +
>> +#ifdef CONFIG_HOTPLUG_CPU
>> +		arch_send_call_function_single_ipi(cpu);
>> +#endif
> 
> Please just provide a stub version of arch_send_call_function_single_ipi
> for the !CONFIG_HOTPLUG_CPU case instead of the ifdef here.
> 

Done.

>> +#ifdef CONFIG_HOTPLUG_CPU
>> +int can_hotplug_cpu(void)
> 
> This should be a bool.
> 
>> +{
>> +	if (cpu_ops.cpu_die)
>> +		return 1;
>> +	else
>> +		return 0;
>> +}
> 
> 	return cpu_ops.cpu_die != NULL;
> 
>> +void default_cpu_die(unsigned int cpu)
>> +{
>> +	int sipval, sieval, scauseval;
>> +
>> +	/* clear all pending flags */
>> +	csr_write(sip, 0);
>> +	/* clear any previous scause data */
>> +	csr_write(scause, 0);
>> +
>> +	do {
>> +		wait_for_interrupt();
>> +		sipval = csr_read(sip);
>> +		sieval = csr_read(sie);
>> +		scauseval = csr_read(scause);
>> +	/* only break if wfi returns for an enabled interrupt */
>> +	} while ((sipval & sieval) == 0 &&
>> +		 scauseval != INTERRUPT_CAUSE_SOFTWARE);
>> +
>> +	boot_sec_cpu();
>> +}
> 
> I suspect all of this except for the boot_sec_cpu() should go into
> a helper in irq.c.  

ok. I will try that. That will also solve interrupt cause declarations 
issue. So I can drop patch 4.

Also as-is this probably doesn't work as scauseval
> will have INTERRUPT_CAUSE_FLAG set, making the comparism never true.
> 

Oops. Thanks for catching that. scauseval is declared as int which made 
this code to work. Fixed it.


Regards,
Atish