From 6fa3db464e3bbe60232169195713902113900806 Mon Sep 17 00:00:00 2001
From: sigsegv7 <ian@vegaa.systems>
Date: Thu, 14 Sep 2023 03:37:37 -0400
Subject: kernel: acpi: Add IRQ to GSI function

Signed-off-by: sigsegv7 <ian@vegaa.systems>
---
 sys/firmware/acpi/acpi_madt.c    | 34 ++++++++++++++++++++++++++++++++++
 sys/include/firmware/acpi/acpi.h |  1 +
 2 files changed, 35 insertions(+)

diff --git a/sys/firmware/acpi/acpi_madt.c b/sys/firmware/acpi/acpi_madt.c
index fde5dde..bf3007b 100644
--- a/sys/firmware/acpi/acpi_madt.c
+++ b/sys/firmware/acpi/acpi_madt.c
@@ -84,6 +84,40 @@ do_parse(void)
     }
 }
 
+/*
+ * Converts IRQ numbers to its corresponding
+ * Global System Interrupt (GSI) number.
+ *
+ * @irq: IRQ number.
+ */
+uint32_t
+irq_to_gsi(uint8_t irq)
+{
+    struct apic_header *hdr = NULL;
+    struct interrupt_override *override = NULL;
+    uint8_t *cur = NULL;
+    uint8_t *end = NULL;
+
+    cur = (uint8_t *)(madt + 1);
+    end = (uint8_t *)madt + madt->hdr.length;
+
+    while (cur < end) {
+        hdr = (void *)cur;
+
+        switch (hdr->type) {
+        case APIC_TYPE_INTERRUPT_OVERRIDE:
+            override = (struct interrupt_override *)cur;
+            if (override->source == irq) {
+                return override->interrupt;
+            }
+        }
+
+        cur += hdr->length;
+    }
+
+    return irq;
+}
+
 void
 acpi_parse_madt(void)
 {
diff --git a/sys/include/firmware/acpi/acpi.h b/sys/include/firmware/acpi/acpi.h
index 049ea58..a3882e2 100644
--- a/sys/include/firmware/acpi/acpi.h
+++ b/sys/include/firmware/acpi/acpi.h
@@ -34,6 +34,7 @@
 #include <sys/types.h>
 
 void acpi_init(void);
+uint32_t irq_to_gsi(uint8_t irq);
 void *acpi_query(const char *query);
 bool acpi_is_checksum_valid(struct acpi_header *hdr);
 struct acpi_root_sdt *acpi_get_root_sdt(void);
-- 
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