Date: Wed, 5 Apr 2017 13:46:34 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Dou Liyang <douly.fnst@cn.fujitsu.com>
cc: x86@kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org,
        ebiederm@xmission.com, bhe@redhat.com, hpa@zytor.com,
        izumi.taku@jp.fujitsu.com
Subject: Re: [RFC PATCH 2/6] x86/apic: Construct a framework for setuping
 APIC mode as soon as possible
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References: <1490799333-18242-1-git-send-email-douly.fnst@cn.fujitsu.com> <1490799333-18242-3-git-send-email-douly.fnst@cn.fujitsu.com>
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On Wed, 29 Mar 2017, Dou Liyang wrote:

> Now, there are two ways to setup local apic and io-apic in X86 arch:
>   1. In an SMP-capable system, it will be done when preparing the
> cpus in native_smp_prepare_boot_cpu().
>   2. If UP_LATE_INIT is y, it will be done in smp_init()
> 
> And, there are many switches in kernel which can determine the way of
> APIC mode setup, as shown below:
> 
>   1. kconfig :
>      CONFIG_X86_64; CONFIG_X86_LOCAL_APIC; CONFIG_x86_IO_APIC
>   2. kernel option: disable_apic; skip_ioapic_setup
>   3. BIOS : boot_cpu_has(X86_FEATURE_APIC)
>   4. MP table: smp_found_config
>   5. ACPI: acpi_lapic; acpi_ioapic; nr_ioapic
> 
> The setup is late which cause the dump-capture kernel hangs with 'notsc'
> option in 1st kernel option. and the use of these switches is messily.
> 
> Before make the APIC mode setup earlier, construct a framework first to
> prepare for the work and make the logic clear.

Calling that a framework is slightly exaggerated. It's a selector function
for the interrupt delivery mode.

>  #ifdef CONFIG_X86_X2APIC
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index f4fc949..bf4ccd0 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -1153,6 +1153,63 @@ void __init sync_Arb_IDs(void)
>  			APIC_INT_LEVELTRIG | APIC_DM_INIT);
>  }
>  
> +enum apic_bsp_mode {
> +	APIC_BSP_MODEL_PIC = 0,
> +	APIC_BSP_MODEL_VIRTUAL_WIRE,
> +	APIC_BSP_MODEL_SYMMETRIC_IO,
> +	APIC_BSP_MODEL_COUNT
> +};
> +
> +static int __init apic_bsp_mode_check(void)
> +{
> +
> +	/* Check kernel option */
> +	if (disable_apic) {
> +		pr_info("APIC disabled by kernel option\n");

kernel option is ambiguous. "APIC disabled via kernel command line" is telling
clearly where this comes from.

> +		return APIC_BSP_MODEL_PIC;
> +	}
> +	/* Check BOIS */
> +#ifdef CONFIG_X86_64
> +	/* On 64-bit, The APIC is integrated, So, must have APIC feature */
> +	if (!boot_cpu_has(X86_FEATURE_APIC)) {
> +		disable_apic = 1;
> +		pr_info("Apic disabled by BIOS\n");

Please use APIC consistently. 

> +		return APIC_BSP_MODEL_PIC;
> +	}
> +#else
> +	if (!boot_cpu_has(X86_FEATURE_APIC) &&
> +		APIC_INTEGRATED(boot_cpu_apic_version)) {
> +		pr_err("BIOS bug, local APIC #%d not detected!...\n",
> +			boot_cpu_physical_apicid);

Please make that

		pr_err(FW_BUG, "Local APIC %d not detected, force emulation",
		       boot_cpu_physical_apicid);

and for consistency reasosns this should also set disable_apic to 1.

> +		return APIC_BSP_MODEL_PIC;
> +	}
> +#endif
> +	/*
> +	 * Check MP table, if neither an integrated nor a separate chip
> +	 * doesn't exist.
> +	 */
> +	if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
> +		pr_info("BOIS don't support APIC, and no SMP configuration.\n");

s/BOIS/BIOS/

and for consistency reasosns this should also set disable_apic to 1.


> +		return APIC_BSP_MODEL_PIC;
> +	}
> +
> +	/* Check MP table, ps: if the virtual wire has been setup */
> +	if (!smp_found_config) {
> +		disable_ioapic_support();
> +
> +		/* Check local APIC, if SMP_NO_CONFIG */
> +		if (!acpi_lapic)
> +			pr_info("SMP motherboard not detected\n");
> +
> +		return APIC_BSP_MODEL_VIRTUAL_WIRE;
> +	}
> +
> +	/* Other checks of ACPI options will be done in each setup function */
> +
> +	return APIC_BSP_MODEL_SYMMETRIC_IO;
> +}
> +
>  /*
>   * Setup the through-local-APIC virtual wire mode.
>   */
> @@ -1202,6 +1259,22 @@ void apic_virture_wire_mode_setup(void)
>  	apic_write(APIC_LVT1, value);
>  }
>  
> +/* init the interrupt routing model for the BSP */
> +void __init init_bsp_APIC(void)
> +{
> +	switch (apic_bsp_mode_check()) {
> +	case APIC_BSP_MODEL_PIC:
> +		pr_info("Keep in PIC mode(8259)\n");
> +		return;
> +	case APIC_BSP_MODEL_VIRTUAL_WIRE:
> +		pr_info("switch to virtual wire model.\n");

Please consistenly start sentences with upper case letters.

Thanks,

	tglx