5 files changed, 43 insertions, 2 deletions

diff --git a/arch/i386/kernel/acpi/boot.c b/arch/i386/kernel/acpi/boot.c
index b7808a89d945..34ee500c26e5 100644
--- a/arch/i386/kernel/acpi/boot.c
+++ b/arch/i386/kernel/acpi/boot.c
@@ -833,6 +833,9 @@ acpi_process_madt(void)
                 if (!error) {
                         acpi_lapic = 1;
 
+#ifdef CONFIG_X86_GENERICARCH
+                        generic_bigsmp_probe();
+#endif
                         /*
                          * Parse MADT IO-APIC entries
                          */
diff --git a/arch/i386/kernel/mpparse.c b/arch/i386/kernel/mpparse.c
index ce838abb27d8..788efffa9930 100644
--- a/arch/i386/kernel/mpparse.c
+++ b/arch/i386/kernel/mpparse.c
@@ -65,6 +65,8 @@ int nr_ioapics;
 int pic_mode;
 unsigned long mp_lapic_addr;
 
+unsigned int def_to_bigsmp = 0;
+
 /* Processor that is doing the boot up */
 unsigned int boot_cpu_physical_apicid = -1U;
 /* Internal processor count */
@@ -213,6 +215,13 @@ static void __init MP_processor_info (struct mpc_config_processor *m)
                 ver = 0x10;
         }
         apic_version[m->mpc_apicid] = ver;
+        if ((num_processors > 8) &&
+            APIC_XAPIC(ver) &&
+            (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL))
+                def_to_bigsmp = 1;
+        else
+                def_to_bigsmp = 0;
+
         bios_cpu_apicid[num_processors - 1] = m->mpc_apicid;
 }
 
diff --git a/arch/i386/kernel/setup.c b/arch/i386/kernel/setup.c
index 9adbf710ec8d..294bcca985ab 100644
--- a/arch/i386/kernel/setup.c
+++ b/arch/i386/kernel/setup.c
@@ -1585,8 +1585,14 @@ void __init setup_arch(char **cmdline_p)
          */
         acpi_boot_table_init();
         acpi_boot_init();
-#endif
 
+#if defined(CONFIG_SMP) && defined(CONFIG_X86_PC)
+        if (def_to_bigsmp)
+                printk(KERN_WARNING "More than 8 CPUs detected and "
+                        "CONFIG_X86_PC cannot handle it.\nUse "
+                        "CONFIG_X86_GENERICARCH or CONFIG_X86_BIGSMP.\n");
+#endif
+#endif
 #ifdef CONFIG_X86_LOCAL_APIC
         if (smp_found_config)
                 get_smp_config();
diff --git a/arch/i386/mach-generic/bigsmp.c b/arch/i386/mach-generic/bigsmp.c
index 25883b44f625..037b2af1a1f4 100644
--- a/arch/i386/mach-generic/bigsmp.c
+++ b/arch/i386/mach-generic/bigsmp.c
@@ -47,7 +47,10 @@ static struct dmi_system_id __initdata bigsmp_dmi_table[] = {
 
 static __init int probe_bigsmp(void)
 { 
-        dmi_check_system(bigsmp_dmi_table);
+        if (def_to_bigsmp)
+                dmi_bigsmp = 1;
+        else
+                dmi_check_system(bigsmp_dmi_table);
         return dmi_bigsmp; 
 } 
 
diff --git a/arch/i386/mach-generic/probe.c b/arch/i386/mach-generic/probe.c
index 5497c65a8790..cea5b3ce4b57 100644
--- a/arch/i386/mach-generic/probe.c
+++ b/arch/i386/mach-generic/probe.c
@@ -30,6 +30,25 @@ struct genapic *apic_probe[] __initdata = {
         NULL,
 };
 
+static int cmdline_apic;
+
+void __init generic_bigsmp_probe(void)
+{
+        /*
+         * This routine is used to switch to bigsmp mode when
+         * - There is no apic= option specified by the user
+         * - generic_apic_probe() has choosen apic_default as the sub_arch
+         * - we find more than 8 CPUs in acpi LAPIC listing with xAPIC support
+         */
+
+        if (!cmdline_apic && genapic == &apic_default)
+                if (apic_bigsmp.probe()) {
+                        genapic = &apic_bigsmp;
+                        printk(KERN_INFO "Overriding APIC driver with %s\n",
+                               genapic->name);
+                }
+}
+
 void __init generic_apic_probe(char *command_line) 
 { 
         char *s;
@@ -52,6 +71,7 @@ void __init generic_apic_probe(char *command_line)
                 if (!changed)
                         printk(KERN_ERR "Unknown genapic `%s' specified.\n", s);
                 *p = old;
+                cmdline_apic = changed;
         } 
         for (i = 0; !changed && apic_probe[i]; i++) { 
                 if (apic_probe[i]->probe()) {