2 files changed, 50 insertions, 3 deletions

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 2d76f022adc2..0b993511e0c5 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -780,8 +780,35 @@ EXPORT_SYMBOL(acpi_unmap_lsapic);
 
 int acpi_register_ioapic(acpi_handle handle, u64 phys_addr, u32 gsi_base)
 {
-        /* TBD */
-        return -EINVAL;
+        int ret = -ENOSYS;
+#ifdef CONFIG_ACPI_HOTPLUG_IOAPIC
+        int ioapic_id;
+        u64 addr;
+        struct ioapic_domain_cfg cfg = {
+                .type = IOAPIC_DOMAIN_DYNAMIC,
+                .ops = &acpi_irqdomain_ops,
+        };
+
+        ioapic_id = acpi_get_ioapic_id(handle, gsi_base, &addr);
+        if (ioapic_id < 0) {
+                unsigned long long uid;
+                acpi_status status;
+
+                status = acpi_evaluate_integer(handle, METHOD_NAME__UID,
+                                               NULL, &uid);
+                if (ACPI_FAILURE(status)) {
+                        acpi_handle_warn(handle, "failed to get IOAPIC ID.\n");
+                        return -EINVAL;
+                }
+                ioapic_id = (int)uid;
+        }
+
+        mutex_lock(&acpi_ioapic_lock);
+        ret  = mp_register_ioapic(ioapic_id, phys_addr, gsi_base, &cfg);
+        mutex_unlock(&acpi_ioapic_lock);
+#endif
+
+        return ret;
 }
 
 EXPORT_SYMBOL(acpi_register_ioapic);
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 4333a751937d..826f44f0a2bf 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -3861,7 +3861,13 @@ static int bad_ioapic_register(int idx)
 
 static int find_free_ioapic_entry(void)
 {
-        return nr_ioapics;
+        int idx;
+
+        for (idx = 0; idx < MAX_IO_APICS; idx++)
+                if (ioapics[idx].nr_registers == 0)
+                        return idx;
+
+        return MAX_IO_APICS;
 }
 
 /**
@@ -3874,6 +3880,7 @@ static int find_free_ioapic_entry(void)
 int mp_register_ioapic(int id, u32 address, u32 gsi_base,
                        struct ioapic_domain_cfg *cfg)
 {
+        bool hotplug = !!ioapic_initialized;
         struct mp_ioapic_gsi *gsi_cfg;
         int idx, ioapic, entries;
         u32 gsi_end;
@@ -3935,6 +3942,19 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
         ioapics[idx].irqdomain = NULL;
         ioapics[idx].irqdomain_cfg = *cfg;
 
+        /*
+         * If mp_register_ioapic() is called during early boot stage when
+         * walking ACPI/SFI/DT tables, it's too early to create irqdomain,
+         * we are still using bootmem allocator. So delay it to setup_IO_APIC().
+         */
+        if (hotplug) {
+                if (mp_irqdomain_create(idx)) {
+                        clear_fixmap(FIX_IO_APIC_BASE_0 + idx);
+                        return -ENOMEM;
+                }
+                alloc_ioapic_saved_registers(idx);
+        }
+
         if (gsi_cfg->gsi_end >= gsi_top)
                 gsi_top = gsi_cfg->gsi_end + 1;
         if (nr_ioapics <= idx)