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

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  [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt delivery mode Dou Liyang <douly.fnst@cn.fujitsu.com> - 2017-06-30 06:10 +0200
    Re: [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt  delivery mode Thomas Gleixner <tglx@linutronix.de> - 2017-07-02 19:40 +0200
      Re: [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt  delivery mode Dou Liyang <douly.fnst@cn.fujitsu.com> - 2017-07-03 03:50 +0200

#1678449 — [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt delivery mode

Now, there are many switches in kernel which are used to determine
the final interrupt delivery mode, 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) CPU Capability: boot_cpu_has(X86_FEATURE_APIC)
4) MP table: smp_found_config
5) ACPI: acpi_lapic; acpi_ioapic; nr_ioapic

These switches are disordered and scattered and there are also some
dependencies with each other. These make the code difficult to
maintain and read.

Construct a selector to unify them into a single function, then,
Use this selector to get an interrupt delivery mode directly.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
---
 arch/x86/kernel/apic/apic.c | 60 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 2d75faf..88be65e 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1157,6 +1157,66 @@ void __init sync_Arb_IDs(void)
 			APIC_INT_LEVELTRIG | APIC_DM_INIT);
 }
 
+enum apic_intr_mode {
+	APIC_PIC,
+	APIC_VIRTUAL_WIRE,
+	APIC_SYMMETRIC_IO,
+};
+
+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)) {
+		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;
+	}
+#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 */
+
+	return APIC_SYMMETRIC_IO;
+}
+
 /*
  * An initial setup of the virtual wire mode.
  */
-- 
2.5.5

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#1679540 — Re: [PATCH v5 01/12] x86/apic: Construct a selector for the interrupt delivery mode

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

> +		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.

> +#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.

> +	return APIC_SYMMETRIC_IO;
> +}

Thanks,

	tglx

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#1679599 — 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
>
>
>

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