From 4fa5b8f2a5e73ffed770c7e47dd625ea62106f7e Mon Sep 17 00:00:00 2001
From: Rafal Kupiec <belliash@codingworkshop.eu.org>
Date: Fri, 2 Feb 2024 22:07:28 +0100
Subject: [PATCH] Implement AcGetApicBase()

---
 xtldr/modules/acpi/acpi.c          | 39 ++++++++++++++++++++++++++++++
 xtldr/modules/acpi/includes/acpi.h |  4 +++
 2 files changed, 43 insertions(+)

diff --git a/xtldr/modules/acpi/acpi.c b/xtldr/modules/acpi/acpi.c
index 6917253..005870d 100644
--- a/xtldr/modules/acpi/acpi.c
+++ b/xtldr/modules/acpi/acpi.c
@@ -48,6 +48,45 @@ AcGetAcpiDescriptionPointer(OUT PVOID *AcpiTable)
     return STATUS_EFI_NOT_FOUND;
 }
 
+/**
+ * Gets the Advanced Programmable Interrupt Controller (APIC) base address.
+ *
+ * @param ApicBase
+ *        Supplies a pointer to memory area where APIC base address will be stored.
+ *
+ * @return This routine returns an EFI status code.
+ *
+ * @since XT 1.0
+ */
+XTCDECL
+EFI_STATUS
+AcGetApicBase(OUT PVOID *ApicBase)
+{
+    PCPUID_REGISTERS CpuRegisters = NULL;
+
+    /* Get CPU features list */
+    CpuRegisters->Leaf = CPUID_GET_CPU_FEATURES;
+    CpuRegisters->SubLeaf = 0;
+    CpuRegisters->Eax = 0;
+    CpuRegisters->Ebx = 0;
+    CpuRegisters->Ecx = 0;
+    CpuRegisters->Edx = 0;
+    ArCpuId(CpuRegisters);
+
+    /* Check if APIC present */
+    if((CpuRegisters->Edx & CPUID_FEATURES_EDX_APIC) == 0)
+    {
+        /* APIC is not supported by the CPU */
+        return STATUS_EFI_UNSUPPORTED;
+    }
+
+    /* Get APIC base address */
+    *ApicBase = (PVOID)((UINT_PTR)ArReadModelSpecificRegister(0x1B) & 0xFFFFF000);
+
+    /* Return success */
+    return STATUS_EFI_SUCCESS;
+}
+
 /**
  * Gets RSDP (ACPI 1.0) from EFI system configuration
  *
diff --git a/xtldr/modules/acpi/includes/acpi.h b/xtldr/modules/acpi/includes/acpi.h
index 4bf4977..19fa8bb 100644
--- a/xtldr/modules/acpi/includes/acpi.h
+++ b/xtldr/modules/acpi/includes/acpi.h
@@ -18,6 +18,10 @@ XTCDECL
 EFI_STATUS
 AcGetAcpiDescriptionPointer(OUT PVOID *AcpiTable);
 
+XTCDECL
+EFI_STATUS
+AcGetApicBase(OUT PVOID *ApicBase);
+
 XTCDECL
 EFI_STATUS
 AcGetRsdpTable(OUT PVOID *AcpiTable);