From f85dbe582f13dc9f415f0e5e4a883f9173c60195 Mon Sep 17 00:00:00 2001
From: Undefine <undefine@undefine.pl>
Date: Fri, 6 Nov 2026 18:54:51 +0100
Subject: [PATCH] Kernel: Add read_generic_address

This will be needed to properly implement ACPI shutdown. It's also
missing PCI configuration space support unlike write_generic_address,
because it would require messing with the PCI subsystem and it's not
necessary for now.
---
 Kernel/Firmware/ACPI/GenericAddress.cpp | 54 +++++++++++++++++++++++++
 Kernel/Firmware/ACPI/GenericAddress.h   |  1 +
 2 files changed, 55 insertions(+)

diff --git a/Kernel/Firmware/ACPI/GenericAddress.cpp b/Kernel/Firmware/ACPI/GenericAddress.cpp
index b0e65e51ac1..4c48dbb130c 100644
--- a/Kernel/Firmware/ACPI/GenericAddress.cpp
+++ b/Kernel/Firmware/ACPI/GenericAddress.cpp
@@ -44,6 +44,60 @@ static ErrorOr<u8> get_bit_width(::ACPI::Structures::GenericAddressStructure con
     return AK::min(bit_width, structure.address_space == ::ACPI::GenericAddressStructure::AddressSpace::SystemIO ? 32 : 64);
 }
 
+ErrorOr<u64> read_generic_address(::ACPI::Structures::GenericAddressStructure const& structure)
+{
+    auto bit_width = TRY(get_bit_width(structure));
+
+    switch (structure.address_space) {
+    case ::ACPI::GenericAddressStructure::AddressSpace::SystemIO: {
+#if ARCH(X86_64)
+        IOAddress address(structure.address);
+        dbgln_if(ACPI_DEBUG, "ACPI: Reading from {}", address);
+
+        switch (bit_width) {
+        case 8:
+            return address.in<u8>();
+        case 16:
+            return address.in<u16>();
+        case 32:
+            return address.in<u32>();
+        default:
+            dbgln("ACPI: Tried to read an unsupported bit width from an IO port");
+            return EINVAL;
+        }
+#else
+        dbgln("ACPI: Tried to access SystemIO on a non x86 architecture");
+        return EINVAL;
+#endif
+    }
+
+    case ::ACPI::GenericAddressStructure::AddressSpace::SystemMemory: {
+        dbgln_if(ACPI_DEBUG, "ACPI: Reading from {}", PhysicalAddress(structure.address));
+
+        switch (bit_width) {
+        case 8:
+            return *TRY(Memory::map_typed<u8>(PhysicalAddress(structure.address)));
+        case 16:
+            return *TRY(Memory::map_typed<u16>(PhysicalAddress(structure.address)));
+        case 32:
+            return *TRY(Memory::map_typed<u32>(PhysicalAddress(structure.address)));
+        case 64:
+            return *TRY(Memory::map_typed<u64>(PhysicalAddress(structure.address)));
+
+        default:
+            dbgln("ACPI: Tried to read an unsupported bit width from SystemMemory");
+            return EINVAL;
+        }
+    }
+
+    default:
+        dbgln("ACPI: Tried to access an unsupported address space");
+        return EINVAL;
+    }
+
+    VERIFY_NOT_REACHED();
+}
+
 ErrorOr<void> write_generic_address(::ACPI::Structures::GenericAddressStructure const& structure, u64 value)
 {
     auto bit_width = TRY(get_bit_width(structure));
diff --git a/Kernel/Firmware/ACPI/GenericAddress.h b/Kernel/Firmware/ACPI/GenericAddress.h
index 3af8fb76227..68b79f425a2 100644
--- a/Kernel/Firmware/ACPI/GenericAddress.h
+++ b/Kernel/Firmware/ACPI/GenericAddress.h
@@ -11,6 +11,7 @@
 
 namespace Kernel::ACPI {
 
+ErrorOr<u64> read_generic_address(::ACPI::Structures::GenericAddressStructure const& structure);
 ErrorOr<void> write_generic_address(::ACPI::Structures::GenericAddressStructure const& structure, u64 value);
 
 }