Disable async compute for D3D12 [Hold] (#301)

* disable async on d3d12

* Change doc

Author: FrancescoC-unity

com.unity.render-pipelines.high-definition/Documentation~/Frame-Settings.md

@@ -93,6 +93,7 @@ These settings control lighting features for your rendering components. Here you
 ### Asynchronous Compute Shaders
 
 These settings control which effects, if any, can make use execute compute Shader commands in parallel.
+Note that these settings will have an effect only if asynchronous compute is supported by the target platform.
 
 | **Property**                       | **Description**                                              |
 | ---------------------------------- | ------------------------------------------------------------ |

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Settings/FrameSettings.cs

@@ -765,7 +765,8 @@ internal static void Sanitize(ref FrameSettings sanitizedFrameSettings, Camera c
             sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.Distortion] &= renderPipelineSettings.supportDistortion && !msaa && !preview;
             sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.LowResTransparent] &= renderPipelineSettings.lowresTransparentSettings.enabled;
 
-            bool async = sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.AsyncCompute] &= SystemInfo.supportsAsyncCompute;
+            // NOTE: We currently disable async compute on D3D12 for an issue we have with constant buffer update. TODO We need to renable it when case 1238431 is resolved
+            bool async = sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.AsyncCompute] &= (SystemInfo.supportsAsyncCompute && SystemInfo.graphicsDeviceType != GraphicsDeviceType.Direct3D12);
             sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.LightListAsync] &= async;
             sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.SSRAsync] &= (async && !rayTracingActive);
             sanitizedFrameSettings.bitDatas[(int)FrameSettingsField.SSAOAsync] &= (async && !rayTracingActive);