linux-kernel - Re: [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt delivery mode

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Date:   Mon, 3 Jul 2017 09:44:09 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <xen-devel@...ts.xenproject.org>, <mingo@...nel.org>,
        <hpa@...or.com>, <ebiederm@...ssion.com>, <bhe@...hat.com>,
        <boris.ostrovsky@...cle.com>, <peterz@...radead.org>,
        <izumi.taku@...fujitsu.com>
Subject: Re: [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt
 delivery mode

Hi Thomas,

At 07/03/2017 01:37 AM, Thomas Gleixner wrote:
> On Fri, 30 Jun 2017, Dou Liyang wrote:
>> +static int __init apic_intr_mode_select(void)
>> +{
>> +	/* Check kernel option */
>> +	if (disable_apic) {
>> +		pr_info("APIC disabled via kernel command line\n");
>> +		return APIC_PIC;
>> +	}
>> +
>> +	/* Check BIOS */
>> +#ifdef CONFIG_X86_64
>> +	/* On 64-bit, the APIC must be integrated, Check local APIC only */
>> +	if (!boot_cpu_has(X86_FEATURE_APIC)) {
>> +		disable_apic = 1;
>> +		pr_info("APIC disabled by BIOS\n");
>> +		return APIC_PIC;
>> +	}
>> +#else
>> +	/*
>> +	 * On 32-bit, check whether there is a separate chip or integrated
>> +	 * APIC
>> +	 */
>> +
>> +	/* Has a local APIC ? */
>> +	if (!boot_cpu_has(X86_FEATURE_APIC) &&
>> +		APIC_INTEGRATED(boot_cpu_apic_version)) {
>
> This looks wrong. The existing logic is:
>
> 	if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config)
> 		return -1;
>
> 	if (!boot_cpu_has(X86_FEATURE_APIC) &&
> 	                APIC_INTEGRATED(boot_cpu_apic_version)) {
> 		pr_err(....);
>
> I know that this is magically the same because boot_cpu_apic_version is 0
> in the !boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config case, so you
> don't fall into that conditional,

I see, it an unnecessary and surplus thing I did.

  but it's completely non obvious and does
> not really make the code more understandable. Quite the contrary.

You are right.

>
>> +		disable_apic = 1;
>> +		pr_err(FW_BUG "Local APIC %d not detected, force emulation\n",
>> +				       boot_cpu_physical_apicid);
>> +		return APIC_PIC;
>> +	}
>> +
>> +	/* Has a separate chip ? */
>> +	if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
>> +		disable_apic = 1;
>> +
>> +		return APIC_PIC;
>> +	}
>
> So if you move exactly that check above the other then it's clear what's
> going on.

Will keep the order like the existing logic you gave above.

>
>> +#endif
>> +
>> +	/* Check MP table or ACPI MADT configuration */
>> +	if (!smp_found_config) {
>> +		disable_ioapic_support();
>> +
>> +		if (!acpi_lapic)
>> +			pr_info("APIC: ACPI MADT or MP tables are not detected\n");
>> +
>> +		return APIC_VIRTUAL_WIRE;
>> +	}
>> +
>> +	/* Other checks of APIC options will be done in each setup function */
>> +
>
> Please remove the extra new line. It's not helping readability.

Yes, remove right now.

Thanks,
	dou.

>
>> +	return APIC_SYMMETRIC_IO;
>> +}
>
> Thanks,
>
> 	tglx
>
>
>