ACPI: Add support for ResourceSource/IRQ domain mapping

ACPI extended IRQ resources may contain a ResourceSource to specify
an alternate interrupt controller. Introduce acpi_irq_get and use it
to implement ResourceSource/IRQ domain mapping.

The new API is similar to of_irq_get and allows re-initialization
of a platform resource from the ACPI extended IRQ resource, and
provides proper behavior for probe deferral when the domain is not
yet present when called.

Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Agustin Vega-Frias <agustinv@codeaurora.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 5b36974..8e577c2 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1153,4 +1153,14 @@
 static inline int parse_spcr(bool earlycon) { return 0; }
 #endif
 
+#if IS_ENABLED(CONFIG_ACPI_GENERIC_GSI)
+int acpi_irq_get(acpi_handle handle, unsigned int index, struct resource *res);
+#else
+static inline
+int acpi_irq_get(acpi_handle handle, unsigned int index, struct resource *res)
+{
+	return -EINVAL;
+}
+#endif
+
 #endif	/*_LINUX_ACPI_H*/