[RFC Patch V1 0/4] enhance IOAPIC core to support hotplug

[RFC Patch V1 0/4] enhance IOAPIC core to support hotplug

[Jiang Liu]

This patch set enhances IOAPIC core to support IOAPIC hotplug on x86
platforms. It's based on another patch set "use irqdomain to dynamically
allocate IRQ for IOAPIC" at https://lkml.org/lkml/2014/5/27/86

You may pull from 
https://github.com/jiangliu/linux.git ioapic/hotplug

Once passed review, we will use Yinghai's patches to glue IOAPIC
driver and ACPI PCI root driver to handle hotplug events.

Jiang Liu (4):
  x86, irq: refine mp_register_ioapic() to prepare for IOAPIC hotplug
  x86, irq, ACPI: introduce a rwsem to protect IOAPIC operations from
    hotplug
  x86, irq, ACPI: implement interface to support ACPI based IOAPIC
    hot-addition
  x86, irq, ACPI: implement interface to support ACPI based IOAPIC
    hot-removal

 arch/x86/include/asm/io_apic.h |    5 +-
 arch/x86/kernel/acpi/boot.c    |   44 +++++++--
 arch/x86/kernel/apic/io_apic.c |  207 ++++++++++++++++++++++++++++++----------
 3 files changed, 196 insertions(+), 60 deletions(-)

-- 
1.7.10.4

[RFC Patch V1 1/4] x86, irq: refine mp_register_ioapic() to prepare for IOAPIC hotplug

[Jiang Liu]

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
---
 arch/x86/include/asm/io_apic.h |    4 +-
 arch/x86/kernel/apic/io_apic.c |  143 ++++++++++++++++++++++++++--------------
 2 files changed, 94 insertions(+), 53 deletions(-)

diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
index 6b40122bec0c..64379c285435 100644
--- a/arch/x86/include/asm/io_apic.h
+++ b/arch/x86/include/asm/io_apic.h
@@ -181,8 +181,8 @@ extern int mp_find_ioapic_pin(int ioapic, u32 gsi);
 extern u32 mp_pin_to_gsi(int ioapic, int pin);
 extern int mp_map_gsi_to_irq(u32 gsi, unsigned int flags);
 extern void mp_unmap_irq(int irq);
-extern void __init mp_register_ioapic(int id, u32 address, u32 gsi_base,
-				      ioapic_create_domain_fn cb, void *arg);
+extern int mp_register_ioapic(int id, u32 address, u32 gsi_base,
+			      ioapic_create_domain_fn cb, void *arg);
 extern struct irq_domain *mp_irqdomain_create(int ioapic,
 		struct device_node *np, const struct irq_domain_ops *ops);
 extern int mp_irqdomain_map(struct irq_domain *domain, unsigned int virq,
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index c7c84d5c0e57..f70fa239f34b 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -85,6 +85,7 @@ int sis_apic_bug = -1;
 static DEFINE_RAW_SPINLOCK(ioapic_lock);
 static DEFINE_RAW_SPINLOCK(vector_lock);
 static DEFINE_MUTEX(ioapic_mutex);
+static int ioapic_initialized;
 
 struct mp_pin_info {
 	int trigger;
@@ -2920,19 +2921,40 @@ out:
  */
 #define PIC_IRQS	(1UL << PIC_CASCADE_IR)
 
-static void ioapic_create_irqdomains(void)
+static int ioapic_create_irqdomain(int idx)
 {
-	int i, size;
-	struct ioapic *ip;
+	int size;
+	struct ioapic *ip = &ioapics[idx];
 
-	for_each_ioapic(i) {
-		ip = &ioapics[i];
-		size = sizeof(struct mp_pin_info) * mp_ioapic_pin_count(i);
-		ip->pin_info = kzalloc(size, GFP_KERNEL);
-		BUG_ON(!ip->pin_info);
-		if (ip->irqdomain_cb)
-			ip->irqdomain = ip->irqdomain_cb(i, ip->irqdomain_arg);
+	size = sizeof(struct mp_pin_info) * mp_ioapic_pin_count(idx);
+	ip->pin_info = kzalloc(size, GFP_KERNEL);
+	if (ip->pin_info == NULL && ioapic_initialized) {
+		pr_warn("failed to allocate memory IOAPIC pin_info.\n");
+		return -ENOMEM;
 	}
+	BUG_ON(!ip->pin_info);
+
+	if (ip->irqdomain_cb) {
+		ip->irqdomain = ip->irqdomain_cb(idx, ip->irqdomain_arg);
+		if (ip->irqdomain == NULL && ioapic_initialized) {
+			pr_warn("failed to create irqdomain for IOAPIC%d\n",
+				idx);
+			kfree(ip->pin_info);
+			ip->pin_info = NULL;
+			return -ENOMEM;
+		}
+		BUG_ON(!ip->irqdomain);
+	}
+
+	return 0;
+}
+
+static void ioapic_create_irqdomains(void)
+{
+	int idx;
+
+	for_each_ioapic(idx)
+		ioapic_create_irqdomain(idx);
 }
 
 void __init setup_IO_APIC(void)
@@ -2955,6 +2977,8 @@ void __init setup_IO_APIC(void)
 	init_IO_APIC_traps();
 	if (legacy_pic->nr_legacy_irqs)
 		check_timer();
+
+	ioapic_initialized = 1;
 }
 
 /*
@@ -3408,7 +3432,7 @@ io_apic_setup_irq_pin(unsigned int irq, int node, struct io_apic_irq_attr *attr)
 	return ret;
 }
 
-static int __init io_apic_get_redir_entries(int ioapic)
+static int io_apic_get_redir_entries(int ioapic)
 {
 	union IO_APIC_reg_01	reg_01;
 	unsigned long flags;
@@ -3455,7 +3479,7 @@ int __init arch_probe_nr_irqs(void)
 }
 
 #ifdef CONFIG_X86_32
-static int __init io_apic_get_unique_id(int ioapic, int apic_id)
+static int io_apic_get_unique_id(int ioapic, int apic_id)
 {
 	union IO_APIC_reg_00 reg_00;
 	static physid_mask_t apic_id_map = PHYSID_MASK_NONE;
@@ -3530,7 +3554,7 @@ static int __init io_apic_get_unique_id(int ioapic, int apic_id)
 	return apic_id;
 }
 
-static u8 __init io_apic_unique_id(u8 id)
+static u8 io_apic_unique_id(u8 id)
 {
 	if ((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) &&
 	    !APIC_XAPIC(apic_version[boot_cpu_physical_apicid]))
@@ -3539,7 +3563,7 @@ static u8 __init io_apic_unique_id(u8 id)
 		return id;
 }
 #else
-static u8 __init io_apic_unique_id(u8 id)
+static u8 io_apic_unique_id(u8 id)
 {
 	int i;
 	DECLARE_BITMAP(used, 256);
@@ -3553,7 +3577,7 @@ static u8 __init io_apic_unique_id(u8 id)
 }
 #endif
 
-static int __init io_apic_get_version(int ioapic)
+static int io_apic_get_version(int ioapic)
 {
 	union IO_APIC_reg_01	reg_01;
 	unsigned long flags;
@@ -3757,21 +3781,7 @@ int mp_find_ioapic_pin(int ioapic, u32 gsi)
 	return gsi - gsi_cfg->gsi_base;
 }
 
-static __init int bad_ioapic(unsigned long address)
-{
-	if (nr_ioapics >= MAX_IO_APICS) {
-		pr_warn("WARNING: Max # of I/O APICs (%d) exceeded (found %d), skipping\n",
-			MAX_IO_APICS, nr_ioapics);
-		return 1;
-	}
-	if (!address) {
-		pr_warn("WARNING: Bogus (zero) I/O APIC address found in table, skipping!\n");
-		return 1;
-	}
-	return 0;
-}
-
-static __init int bad_ioapic_register(int idx)
+static int bad_ioapic_register(int idx)
 {
 	union IO_APIC_reg_00 reg_00;
 	union IO_APIC_reg_01 reg_01;
@@ -3790,30 +3800,43 @@ static __init int bad_ioapic_register(int idx)
 	return 0;
 }
 
-void __init mp_register_ioapic(int id, u32 address, u32 gsi_base,
-			       ioapic_create_domain_fn cb, void *arg)
+static int find_free_ioapic_entry(void)
+{
+	return nr_ioapics;
+}
+
+int mp_register_ioapic(int id, u32 address, u32 gsi_base,
+		       ioapic_create_domain_fn cb, void *arg)
 {
-	int idx = 0;
-	int entries;
+	u32 gsi_end;
+	int idx, ioapic, entries;
 	struct mp_ioapic_gsi *gsi_cfg;
 
-	if (bad_ioapic(address))
-		return;
+	if (!address) {
+		pr_warn("WARNING: Bogus (zero) I/O APIC address found in table, skipping!\n");
+		return -EINVAL;
+	}
+	for_each_ioapic(ioapic)
+		if (ioapics[ioapic].mp_config.apicaddr == address) {
+			pr_warn("address 0x%x conflicts with IOAPIC%d\n",
+				address, ioapic);
+			return -EEXIST;
+		}
 
-	idx = nr_ioapics;
+	idx = find_free_ioapic_entry();
+	if (idx >= MAX_IO_APICS) {
+		pr_warn("WARNING: Max # of I/O APICs (%d) exceeded (found %d), skipping\n",
+			MAX_IO_APICS, idx);
+		return -ENOSPC;
+	}
 
 	ioapics[idx].mp_config.type = MP_IOAPIC;
 	ioapics[idx].mp_config.flags = MPC_APIC_USABLE;
 	ioapics[idx].mp_config.apicaddr = address;
-	ioapics[idx].irqdomain_cb = cb;
-	ioapics[idx].irqdomain_arg = arg;
-	ioapics[idx].irqdomain = NULL;
-
 	set_fixmap_nocache(FIX_IO_APIC_BASE_0 + idx, address);
-
 	if (bad_ioapic_register(idx)) {
 		clear_fixmap(FIX_IO_APIC_BASE_0 + idx);
-		return;
+		return -ENODEV;
 	}
 
 	ioapics[idx].mp_config.apicid = io_apic_unique_id(id);
@@ -3824,24 +3847,43 @@ void __init mp_register_ioapic(int id, u32 address, u32 gsi_base,
 	 * and to prevent reprogramming of IOAPIC pins (PCI GSIs).
 	 */
 	entries = io_apic_get_redir_entries(idx);
+	gsi_end = gsi_base + entries - 1;
+	for_each_ioapic(ioapic) {
+		gsi_cfg = mp_ioapic_gsi_routing(idx);
+		if ((gsi_base >= gsi_cfg->gsi_base &&
+		     gsi_base <= gsi_cfg->gsi_end) ||
+		    (gsi_end >= gsi_cfg->gsi_base &&
+		     gsi_end <= gsi_cfg->gsi_end)) {
+			pr_warn("GSI range [%u-%u] for new IOAPIC conflicts with GSI[%u-%u]\n",
+				gsi_base, gsi_end,
+				gsi_cfg->gsi_base, gsi_cfg->gsi_end);
+			clear_fixmap(FIX_IO_APIC_BASE_0 + idx);
+			return -EEXIST;
+		}
+	}
 	gsi_cfg = mp_ioapic_gsi_routing(idx);
 	gsi_cfg->gsi_base = gsi_base;
-	gsi_cfg->gsi_end = gsi_base + entries - 1;
+	gsi_cfg->gsi_end = gsi_end;
 
-	/*
-	 * The number of IO-APIC IRQ registers (== #pins):
-	 */
-	ioapics[idx].nr_registers = entries;
+	ioapics[idx].irqdomain_cb = cb;
+	ioapics[idx].irqdomain_arg = arg;
+	ioapics[idx].irqdomain = NULL;
 
 	if (gsi_cfg->gsi_end >= gsi_top)
 		gsi_top = gsi_cfg->gsi_end + 1;
 
+	if (nr_ioapics <= idx)
+		nr_ioapics = idx + 1;
+
+	/* Set nr_registers to mark entry present */
+	ioapics[idx].nr_registers = entries;
+
 	pr_info("IOAPIC[%d]: apic_id %d, version %d, address 0x%x, GSI %d-%d\n",
 		idx, mpc_ioapic_id(idx),
 		mpc_ioapic_ver(idx), mpc_ioapic_addr(idx),
 		gsi_cfg->gsi_base, gsi_cfg->gsi_end);
 
-	nr_ioapics++;
+	return 0;
 }
 
 struct irq_domain *mp_irqdomain_create(int ioapic, struct device_node *np,
@@ -3852,8 +3894,7 @@ struct irq_domain *mp_irqdomain_create(int ioapic, struct device_node *np,
 	int hwirqs = mp_ioapic_pin_count(ioapic);
 
 	domain = irq_domain_add_linear(np, hwirqs, ops, (void *)(long)ioapic);
-	BUG_ON(!domain);
-	if (gsi_cfg->gsi_base == 0)
+	if (domain && gsi_cfg->gsi_base == 0)
 		irq_set_default_host(domain);
 
 	return domain;
-- 
1.7.10.4

Re: [RFC Patch V1 1/4] x86, irq: refine mp_register_ioapic() to prepare for IOAPIC hotplug

[Thomas Gleixner]

On Tue, 27 May 2014, Jiang Liu wrote:

> -static void ioapic_create_irqdomains(void)
> +static int ioapic_create_irqdomain(int idx)

...

> -static int __init io_apic_get_redir_entries(int ioapic)
> +static int io_apic_get_redir_entries(int ioapic)

Can you please split the functional changes from the trivial __init
removal ones?

Thanks,

	tglx

[RFC Patch V1 2/4] x86, irq, ACPI: introduce a rwsem to protect IOAPIC operations from hotplug

[Jiang Liu]

We are going to support ACPI based IOAPIC hotplug, so introduce a rwsem
to protect IOAPIC data structures from IOAPIC hotplug. We choose to
serialize in ACPI instead of in the IOAPIC core because:
1) currently we are only plan to support ACPI based IOAPIC hotplug
2) it's much more clean and easy
3) It does't affect IOAPIC discovered by devicetree, SFI and mppparse.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
---
 arch/x86/kernel/acpi/boot.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index c8e8fe67bbc8..a1b388e88bcb 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -75,6 +75,8 @@ int acpi_fix_pin2_polarity __initdata;
 static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
 #endif
 
+static DECLARE_RWSEM(acpi_ioapic_rwsem);
+
 #ifndef __HAVE_ARCH_CMPXCHG
 #warning ACPI uses CMPXCHG, i486 and later hardware
 #endif
@@ -495,8 +497,11 @@ void __init acpi_pic_sci_set_trigger(unsigned int irq, u16 trigger)
 
 int acpi_gsi_to_irq(u32 gsi, unsigned int *irqp)
 {
-	int irq = mp_map_gsi_to_irq(gsi, IOAPIC_MAP_ALLOC | IOAPIC_MAP_CHECK);
+	int irq;
 
+	down_read(&acpi_ioapic_rwsem);
+	irq = mp_map_gsi_to_irq(gsi, IOAPIC_MAP_ALLOC | IOAPIC_MAP_CHECK);
+	up_read(&acpi_ioapic_rwsem);
 	if (irq >= 0) {
 		*irqp = irq;
 		return 0;
@@ -537,7 +542,9 @@ static int acpi_register_gsi_ioapic(struct device *dev, u32 gsi,
 	int irq = gsi;
 
 #ifdef CONFIG_X86_IO_APIC
+	down_read(&acpi_ioapic_rwsem);
 	irq = mp_register_gsi(dev, gsi, trigger, polarity);
+	up_read(&acpi_ioapic_rwsem);
 #endif
 
 	return irq;
@@ -546,7 +553,9 @@ static int acpi_register_gsi_ioapic(struct device *dev, u32 gsi,
 static void acpi_unregister_gsi_ioapic(u32 gsi)
 {
 #ifdef CONFIG_X86_IO_APIC
+	down_read(&acpi_ioapic_rwsem);
 	mp_unregister_gsi(gsi);
+	up_read(&acpi_ioapic_rwsem);
 #endif
 }
 
@@ -1198,7 +1207,9 @@ static void __init acpi_process_madt(void)
 			/*
 			 * Parse MADT IO-APIC entries
 			 */
+			down_write(&acpi_ioapic_rwsem);
 			error = acpi_parse_madt_ioapic_entries();
+			up_write(&acpi_ioapic_rwsem);
 			if (!error) {
 				acpi_set_irq_model_ioapic();
 
-- 
1.7.10.4

[RFC Patch V1 3/4] x86, irq, ACPI: implement interface to support ACPI based IOAPIC hot-addition

[Jiang Liu]

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

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
---
 arch/x86/kernel/acpi/boot.c    |   18 ++++++++++++++++--
 arch/x86/kernel/apic/io_apic.c |   24 +++++++++++++++++++++---
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index a1b388e88bcb..d807e16f8fec 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -655,8 +655,22 @@ 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_X86_IO_APIC
+	unsigned long long uid;
+	acpi_status status;
+
+	status = acpi_evaluate_integer(handle, METHOD_NAME__UID, NULL, &uid);
+	if (ACPI_FAILURE(status))
+		uid = 0;
+
+	down_write(&acpi_ioapic_rwsem);
+	ret  = mp_register_ioapic((int)uid, phys_addr, gsi_base,
+				  acpi_create_irqdomain, NULL);
+	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 f70fa239f34b..4bddff760ff4 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -3802,7 +3802,13 @@ 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;
 }
 
 int mp_register_ioapic(int id, u32 address, u32 gsi_base,
@@ -3818,8 +3824,15 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
 	}
 	for_each_ioapic(ioapic)
 		if (ioapics[ioapic].mp_config.apicaddr == address) {
-			pr_warn("address 0x%x conflicts with IOAPIC%d\n",
-				address, ioapic);
+			/*
+			 * IOAPIC unit may also be visible in PCI scope.
+			 * When ioapic PCI driver's probe() is called,
+			 * the IOAPIC unit may have already been initialized
+			 * at boot time.
+			 */
+			if (!ioapic_initialized)
+				pr_warn("address 0x%x conflicts with IOAPIC%d\n",
+					address, ioapic);
 			return -EEXIST;
 		}
 
@@ -3875,6 +3888,11 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
 	if (nr_ioapics <= idx)
 		nr_ioapics = idx + 1;
 
+	if (ioapic_initialized && ioapic_create_irqdomain(idx)) {
+		clear_fixmap(FIX_IO_APIC_BASE_0 + idx);
+		return -ENOMEM;
+	}
+
 	/* Set nr_registers to mark entry present */
 	ioapics[idx].nr_registers = entries;
 
-- 
1.7.10.4

[RFC Patch V1 4/4] x86, irq, ACPI: implement interface to support ACPI based IOAPIC hot-removal

[Jiang Liu]

Implement acpi_unregister_ioapic() to support ACPI based IOAPIC hot-removal.
An IOAPIC could only be removed when all its pins are unused.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
---
 arch/x86/include/asm/io_apic.h |    1 +
 arch/x86/kernel/acpi/boot.c    |   13 ++++++++----
 arch/x86/kernel/apic/io_apic.c |   46 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
index 64379c285435..256ec8d9050c 100644
--- a/arch/x86/include/asm/io_apic.h
+++ b/arch/x86/include/asm/io_apic.h
@@ -183,6 +183,7 @@ extern int mp_map_gsi_to_irq(u32 gsi, unsigned int flags);
 extern void mp_unmap_irq(int irq);
 extern int mp_register_ioapic(int id, u32 address, u32 gsi_base,
 			      ioapic_create_domain_fn cb, void *arg);
+extern int mp_unregister_ioapic(u32 gsi_base);
 extern struct irq_domain *mp_irqdomain_create(int ioapic,
 		struct device_node *np, const struct irq_domain_ops *ops);
 extern int mp_irqdomain_map(struct irq_domain *domain, unsigned int virq,
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index d807e16f8fec..c17cc0510040 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -672,15 +672,20 @@ int acpi_register_ioapic(acpi_handle handle, u64 phys_addr, u32 gsi_base)
 
 	return ret;
 }
-
 EXPORT_SYMBOL(acpi_register_ioapic);
 
 int acpi_unregister_ioapic(acpi_handle handle, u32 gsi_base)
 {
-	/* TBD */
-	return -EINVAL;
-}
+	int ret = -ENOSYS;
+
+#ifdef CONFIG_X86_IO_APIC
+	down_write(&acpi_ioapic_rwsem);
+	ret  = mp_unregister_ioapic(gsi_base);
+	up_write(&acpi_ioapic_rwsem);
+#endif
 
+	return ret;
+}
 EXPORT_SYMBOL(acpi_unregister_ioapic);
 
 static int __init acpi_parse_sbf(struct acpi_table_header *table)
diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 4bddff760ff4..4343247d15b1 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2949,6 +2949,18 @@ static int ioapic_create_irqdomain(int idx)
 	return 0;
 }
 
+static void ioapic_destroy_irqdomain(int idx)
+{
+	if (ioapics[idx].irqdomain) {
+		irq_domain_remove(ioapics[idx].irqdomain);
+		ioapics[idx].irqdomain = NULL;
+	}
+	if (ioapics[idx].pin_info) {
+		kfree(ioapics[idx].pin_info);
+		ioapics[idx].pin_info = NULL;
+	}
+}
+
 static void ioapic_create_irqdomains(void)
 {
 	int idx;
@@ -3904,6 +3916,40 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
 	return 0;
 }
 
+int mp_unregister_ioapic(u32 gsi_base)
+{
+	int ioapic, pin;
+	int found = 0;
+	struct mp_pin_info *pin_info;
+
+	for_each_ioapic(ioapic)
+		if (ioapics[ioapic].gsi_config.gsi_base == gsi_base) {
+			found = 1;
+			break;
+		}
+	if (!found) {
+		pr_warn("can't find IOAPIC for GSI %d\n", gsi_base);
+		return -ENODEV;
+	}
+
+	for_each_pin(ioapic, pin) {
+		pin_info = mp_pin_info(ioapic, pin);
+		if (pin_info->count) {
+			pr_warn("pin%d on IOAPIC%d is still in use.\n",
+				pin, ioapic);
+			return -EBUSY;
+		}
+	}
+
+	/* Mark entry not present */
+	ioapics[ioapic].nr_registers  = 0;
+	ioapic_destroy_irqdomain(ioapic);
+	clear_fixmap(FIX_IO_APIC_BASE_0 + ioapic);
+	memset(&ioapics[ioapic], 0, sizeof(ioapics[ioapic]));
+
+	return 0;
+}
+
 struct irq_domain *mp_irqdomain_create(int ioapic, struct device_node *np,
 				       const struct irq_domain_ops *ops)
 {
-- 
1.7.10.4