linux-kernel - Re: [PATCH v8 01/13] x86/apic: Construct a selector for the interrupt delivery mode

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Date:   Wed, 6 Sep 2017 18:17:28 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        mingo@...nel.org, hpa@...or.com, rjw@...ysocki.net, bp@...en8.de,
        indou.takao@...fujitsu.com, izumi.taku@...fujitsu.com
Subject: Re: [PATCH v8 01/13] x86/apic: Construct a selector for the
 interrupt delivery mode

Hi Dou,

On 08/28/17 at 11:20am, 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;
> +	}
> +

I am not very familiar with cpu registers, not sure if we can adjust
below code flow as:

	/* If APIC is integrated, check local APIC only */
	if (lapic_is_integrated() && !boot_cpu_has(X86_FEATURE_APIC)) {
		disable_apic = 1;
		pr_info("APIC disabled by BIOS\n");
		return APIC_PIC;
	}

	/* If APIC is on a separate chip, check if smp_found_config is found*/
	if (!lapic_is_integrated() && !smp_found_config) {
		disable_apic = 1;
		return APIC_PIC;
	}
	~~~~ Now, I haven't think of why smp_found_config has to be
             checked here.

In this way, we don't need the CONFIG_X86_64 checking since it's
contained in lapic_is_integrated() already. And the checking is obvious
for understanding. Just not very sure if the checking is adequate.

Just my personal opinion.

> +	/* 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 separate chip ? */
> +	if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
> +		disable_apic = 1;
> +
> +		return APIC_PIC;
> +	}
> +
> +	/* Has a local APIC ? */
> +	if (!boot_cpu_has(X86_FEATURE_APIC) &&
> +		APIC_INTEGRATED(boot_cpu_apic_version)) {
> +		disable_apic = 1;
> +		pr_err(FW_BUG "Local APIC %d not detected, force emulation\n",
> +				       boot_cpu_physical_apicid);
> +
> +		return APIC_PIC;
> +	}
> +#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;
> +	}
> +
> +	return APIC_SYMMETRIC_IO;
> +}
> +
>  /*
>   * An initial setup of the virtual wire mode.
>   */
> -- 
> 2.5.5
> 
> 
>