Introduce ACPI_IRQ_MODEL_GIC which is needed for ARM64 as GIC is
used, and then register device's gsi with the core IRQ subsystem.

acpi_register_gsi() is similar to DT based irq_of_parse_and_map(),
since gsi is unique in the system, so use hwirq number directly
for the mapping.

Originally-by: Amit Daniel Kachhap [off-list ref]
Signed-off-by: Hanjun Guo <redacted>
---
 arch/arm64/kernel/acpi.c |   73 ++++++++++++++++++++++++++++++++++++++++++++++
 drivers/acpi/bus.c       |    3 ++
 include/linux/acpi.h     |    1 +
 3 files changed, 77 insertions(+)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index 35dff11..354b912 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c

@@ -37,6 +37,12 @@ EXPORT_SYMBOL(acpi_pci_disabled);
 static int enabled_cpus;	/* Processors (GICC) with enabled flag in MADT */
 
 /*
+ * Since we're on ARM, the default interrupt routing model
+ * clearly has to be GIC.
+ */
+enum acpi_irq_model_id acpi_irq_model = ACPI_IRQ_MODEL_GIC;
+
+/*
  * __acpi_map_table() will be called before page_init(), so early_ioremap()
  * or early_memremap() should be called here to for ACPI table mapping.
  */

@@ -194,6 +200,73 @@ void __init acpi_smp_init_cpus(void)
 	pr_info("%d CPUs enabled, %d CPUs total\n", enabled_cpus, total_cpus);
 }
 
+int acpi_gsi_to_irq(u32 gsi, unsigned int *irq)
+{
+	*irq = irq_find_mapping(NULL, gsi);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(acpi_gsi_to_irq);