Detect GC region based on the actual region value

The county code isn't 100% reliable for detecting the region.
For instance, some games released in Korea have the country
code E even though they're region-locked to NTSC-J consoles.

This commit makes the GC disc region detection match the Wii
disc region detection (apart from the region value being in
a different place on the disc).

2 files changed, 12 insertions, 6 deletions

diff --git a/Source/Core/DiscIO/Enums.h b/Source/Core/DiscIO/Enums.h
index cce235c38e..7aa06ef4a1 100644
--- a/Source/Core/DiscIO/Enums.h
+++ b/Source/Core/DiscIO/Enums.h
@@ -40,10 +40,10 @@ enum class Country
   NUMBER_OF_COUNTRIES
 };
 
-// Regions 0 - 2 and 4 match Nintendo's Wii region numbering.
+// Regions 0 - 2 and 4 match Nintendo's GameCube/Wii region numbering.
 enum class Region
 {
-  NTSC_J = 0,          // Japan and Taiwan
+  NTSC_J = 0,          // Japan and Taiwan (and South Korea for GameCube only)
   NTSC_U = 1,          // Mainly North America
   PAL = 2,             // Mainly Europe and Oceania
   UNKNOWN_REGION = 3,  // 3 seems to be unused? Anyway, we need an UNKNOWN_REGION. Let's put it here
diff --git a/Source/Core/DiscIO/VolumeGC.cpp b/Source/Core/DiscIO/VolumeGC.cpp
index 1a89917812..5941af4a56 100644
--- a/Source/Core/DiscIO/VolumeGC.cpp
+++ b/Source/Core/DiscIO/VolumeGC.cpp
@@ -60,14 +60,20 @@ std::string VolumeGC::GetGameID(const Partition& partition) const
 
 Region VolumeGC::GetRegion() const
 {
-  const std::optional<u8> country_code = ReadSwapped<u8>(3, PARTITION_NONE);
-  return country_code ? RegionSwitchGC(*country_code) : Region::UNKNOWN_REGION;
+  const std::optional<u32> region_code = ReadSwapped<u32>(0x458, PARTITION_NONE);
+  return region_code ? static_cast<Region>(*region_code) : Region::UNKNOWN_REGION;
 }
 
 Country VolumeGC::GetCountry(const Partition& partition) const
 {
-  const std::optional<u8> country_code = ReadSwapped<u8>(3, partition);
-  return country_code ? CountrySwitch(*country_code) : Country::COUNTRY_UNKNOWN;
+  // The 0 that we use as a default value is mapped to COUNTRY_UNKNOWN and UNKNOWN_REGION
+  const u8 country_byte = ReadSwapped<u8>(3, partition).value_or(0);
+  const Region region = GetRegion();
+
+  if (RegionSwitchGC(country_byte) != region)
+    return TypicalCountryForRegion(region);
+
+  return CountrySwitch(country_byte);
 }
 
 std::string VolumeGC::GetMakerID(const Partition& partition) const