nx2:vi2: reply to 104 with the display's output format

GetHdrStatus returns a u64 output format after the result. The bare
success reply left it to stale reply words, and Fire Emblem: Fortune's
Weave set up HDR output from them: its tone map constants came out NaN
and every frame was black. Report format 1 (SDR) for the "default"
display.

Assisted-by: Claude Opus 5.5 (debugging and drafting)
Signed-off-by: duck912 <350528965+Duck912@users.noreply.github.com>

1 files changed, 23 insertions, 2 deletions

diff --git a/src/core/hle/service/nx2_gsv.h b/src/core/hle/service/nx2_gsv.h
index cb92bc107b..7ef4c2e0e3 100644
--- a/src/core/hle/service/nx2_gsv.h
+++ b/src/core/hle/service/nx2_gsv.h
@@ -1442,10 +1442,10 @@ public:
             {11, &INx2Vi2Session::ReturnEvent, "Unknown11"},
             {31, &INx2Vi2Session::GetVsyncEvent, "GetVsyncEvent (guessed)"},
             {32, &INx2Vi2Session::GetVsyncEvent, "GetDisplayVsyncEvent (guessed)"},
-            // Title 1 calls these ~75 times a second with the display name "default"; the
+            {104, &INx2Vi2Session::GetHdrStatus, "GetHdrStatus"},
+            // Title 1 calls this ~75 times a second with the display name "default"; the
             // auto stub's empty success reply works, but logged two lines per call (a 50 MB log
             // in an 18 minute session).
-            {104, &INx2Vi2Session::SucceedQuietly, "Unknown104 (display \"default\")"},
             {105, &INx2Vi2Session::SucceedQuietly, "Unknown105 (display \"default\")"},
             {228, &INx2Vi2Session::CancelClientBuffer, "CancelClientBuffer"},
             {229, &INx2Vi2Session::PresentClientBuffer, "PresentClientBuffer"},
@@ -1798,6 +1798,27 @@ private:
         TipcReplyWords(ctx, {1});
     }
 
+    // 104(u64 display name): result, u64 output format, u32 0. Format 1 is SDR. A bare success
+    // left the format to stale reply words and a game could set up HDR output from them.
+    void GetHdrStatus(HLERequestContext& ctx) {
+        const auto* packet = ctx.CommandBuffer();
+        const u64 name = u64{packet[2]} | (u64{packet[3]} << 32);
+        constexpr u64 DefaultDisplay = 0x00746c7561666564ULL; // "default"
+        Result result = Kernel::ResultInvalidCombination;
+        u64 format{};
+        if (packet[0] == 0x78 && packet[1] == 2) {
+            result = Result{ErrorModule::VI, 7};
+            if (name == DefaultDisplay) {
+                format = 1;
+                result = ResultSuccess;
+            }
+        }
+        IPC::ResponseBuilder rb{ctx, 5};
+        rb.Push(result.raw);
+        rb.Push(format);
+        rb.Push<u32>(0);
+    }
+
     // The same reply as the auto stub (success, no data), without its log lines.
     void SucceedQuietly(HLERequestContext& ctx) {
         IPC::ResponseBuilder rb{ctx, 2};