From abca04c8f926d781a591f957c46f9c8d9a7a048b Mon Sep 17 00:00:00 2001
From: Shyanne <randomgirlisweird@gmail.com>
Date: Wed, 28 Jan 2026 00:18:21 -0500
Subject: [PATCH] [HLE] Stubbed IUserLocalCommuniationService:SetProtocol (106)

Should fix Animal Crossing: New Horizons crashing on LDN connection and potentially other titles with Switch 2 updates.
---
 .../IUserLocalCommunicationService.cs           | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/Ryujinx.HLE/HOS/Services/Ldn/UserServiceCreator/IUserLocalCommunicationService.cs b/src/Ryujinx.HLE/HOS/Services/Ldn/UserServiceCreator/IUserLocalCommunicationService.cs
index 62a86ad91..abf4153d0 100644
--- a/src/Ryujinx.HLE/HOS/Services/Ldn/UserServiceCreator/IUserLocalCommunicationService.cs
+++ b/src/Ryujinx.HLE/HOS/Services/Ldn/UserServiceCreator/IUserLocalCommunicationService.cs
@@ -487,6 +487,23 @@ namespace Ryujinx.HLE.HOS.Services.Ldn.UserServiceCreator
             return ResultCode.Success;
         }
 
+        [CommandCmif(106)] // 20.0.0+
+        // SetProtocol
+        public ResultCode SetProtocol(ServiceCtx context)
+        {
+            uint protocolValue =  context.RequestData.ReadUInt32();
+
+            // On NX only input value 1 or 3 is allowed, with an error being thrown otherwise.
+            if (protocolValue != 1 || protocolValue != 3)
+            {
+                throw new NotSupportedException($"Protocol value is {protocolValue}!!");
+            }
+            
+            Logger.Info?.PrintMsg(LogClass.ServiceLdn, $"Protocol value:  {protocolValue}");
+            Logger.Stub?.PrintMsg(LogClass.ServiceLdn, "IUserLocalCommunicationService SetProtocol: Stubbed.");
+            return ResultCode.Success;
+        }
+
         [CommandCmif(200)]
         // OpenAccessPoint()
         public ResultCode OpenAccessPoint(ServiceCtx context)