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

[Dou Liyang]

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