x86: Allow platforms to force enable apic

Some embedded x86 platforms don't setup the APIC in the
BIOS/bootloader and would be forced to add "lapic" on the kernel
command line. That's a bit akward.

Split out the force enable code from detect_init_APIC() and allow
platform code to call it from the platform setup. That avoids the
command line parameter and possible replication of the MSR dance in
the force enable code.

Signed-off-by: Thomas Gleixner <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Dirk Brandewie <[e-mail]>

arch/x86/include/asm/apic.h

···
 extern void setup_secondary_APIC_clock(void);
 extern int APIC_init_uniprocessor(void);
 extern void enable_NMI_through_LVT0(void);
+extern int apic_force_enable(void);
 
 /*
  * On 32bit this is mach-xxx local

arch/x86/kernel/apic/apic.c

···
 	return 0;
 }
 #else
+
+static int apic_verify(void)
+{
+	u32 features, h, l;
+
+	/*
+	 * The APIC feature bit should now be enabled
+	 * in `cpuid'
+	 */
+	features = cpuid_edx(1);
+	if (!(features & (1 << X86_FEATURE_APIC))) {
+		pr_warning("Could not enable APIC!\n");
+		return -1;
+	}
+	set_cpu_cap(&boot_cpu_data, X86_FEATURE_APIC);
+	mp_lapic_addr = APIC_DEFAULT_PHYS_BASE;
+
+	/* The BIOS may have set up the APIC at some other address */
+	rdmsr(MSR_IA32_APICBASE, l, h);
+	if (l & MSR_IA32_APICBASE_ENABLE)
+		mp_lapic_addr = l & MSR_IA32_APICBASE_BASE;
+
+	pr_info("Found and enabled local APIC!\n");
+	return 0;
+}
+
+int apic_force_enable(void)
+{
+	u32 h, l;
+
+	if (disable_apic)
+		return -1;
+
+	/*
+	 * Some BIOSes disable the local APIC in the APIC_BASE
+	 * MSR. This can only be done in software for Intel P6 or later
+	 * and AMD K7 (Model > 1) or later.
+	 */
+	rdmsr(MSR_IA32_APICBASE, l, h);
+	if (!(l & MSR_IA32_APICBASE_ENABLE)) {
+		pr_info("Local APIC disabled by BIOS -- reenabling.\n");
+		l &= ~MSR_IA32_APICBASE_BASE;
+		l |= MSR_IA32_APICBASE_ENABLE | APIC_DEFAULT_PHYS_BASE;
+		wrmsr(MSR_IA32_APICBASE, l, h);
+		enabled_via_apicbase = 1;
+	}
+	return apic_verify();
+}
+
 /*
  * Detect and initialize APIC
  */
 static int __init detect_init_APIC(void)
 {
-	u32 h, l, features;
-
 	/* Disabled by kernel option? */
 	if (disable_apic)
 		return -1;
···
 				"you can enable it with \"lapic\"\n");
 			return -1;
 		}
-		/*
-		 * Some BIOSes disable the local APIC in the APIC_BASE
-		 * MSR. This can only be done in software for Intel P6 or later
-		 * and AMD K7 (Model > 1) or later.
-		 */
-		rdmsr(MSR_IA32_APICBASE, l, h);
-		if (!(l & MSR_IA32_APICBASE_ENABLE)) {
-			pr_info("Local APIC disabled by BIOS -- reenabling.\n");
-			l &= ~MSR_IA32_APICBASE_BASE;
-			l |= MSR_IA32_APICBASE_ENABLE | APIC_DEFAULT_PHYS_BASE;
-			wrmsr(MSR_IA32_APICBASE, l, h);
-			enabled_via_apicbase = 1;
-		}
+		if (apic_force_enable())
+			return -1;
+	} else {
+		if (apic_verify())
+			return -1;
 	}
-	/*
-	 * The APIC feature bit should now be enabled
-	 * in `cpuid'
-	 */
-	features = cpuid_edx(1);
-	if (!(features & (1 << X86_FEATURE_APIC))) {
-		pr_warning("Could not enable APIC!\n");
-		return -1;
-	}
-	set_cpu_cap(&boot_cpu_data, X86_FEATURE_APIC);
-	mp_lapic_addr = APIC_DEFAULT_PHYS_BASE;
-
-	/* The BIOS may have set up the APIC at some other address */
-	rdmsr(MSR_IA32_APICBASE, l, h);
-	if (l & MSR_IA32_APICBASE_ENABLE)
-		mp_lapic_addr = l & MSR_IA32_APICBASE_BASE;
-
-	pr_info("Found and enabled local APIC!\n");
 
 	apic_pm_activate();