Implement acpi_register_ioapic() and enhance mp_register_ioapic()
to support ACPI based IOAPIC hot-addition.

Signed-off-by: Jiang Liu <jiang....@linux.intel.com>
---
 arch/x86/kernel/acpi/boot.c    |   31 +++++++++++++++++++++++++++++--
 arch/x86/kernel/apic/io_apic.c |   22 +++++++++++++++++++++-
 2 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 3f6b665f5aa6..8205f6381d77 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -779,8 +779,35 @@ 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;
+       }
+
+       down_write(&acpi_ioapic_rwsem);
+       ret  = mp_register_ioapic(ioapic_id, phys_addr, gsi_base, &cfg);
+       up_write(&acpi_ioapic_rwsem);
+#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 59267659e5b1..4d9d87cc3259 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -3853,7 +3853,13 @@ 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;
 }
 
 /**
@@ -3869,6 +3875,7 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
        u32 gsi_end;
        int idx, ioapic, entries;
        struct mp_ioapic_gsi *gsi_cfg;
+       bool hotplug = !!ioapic_initialized;
 
        if (!address) {
                pr_warn("Bogus (zero) I/O APIC address found, skipping!\n");
@@ -3927,6 +3934,19 @@ 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)
-- 
1.7.10.4

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