From 4ef54169af74f47d0000a45392eea450df553993 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Henrik=20Rydg=C3=A5rd?= <hrydgard@gmail.com>
Date: Sat, 2 Dec 2023 11:34:59 +0100
Subject: [PATCH] Add a compat.ini setting to allow delayed GPU readbacks, for
 experimentation.

---
 Core/Compatibility.cpp                  |  1 +
 Core/Compatibility.h                    |  1 +
 GPU/Common/FramebufferManagerCommon.cpp | 12 ++++++++++--
 assets/compat.ini                       | 12 +++++++++---
 4 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/Core/Compatibility.cpp b/Core/Compatibility.cpp
index 29a8874039..5e2c1205dd 100644
--- a/Core/Compatibility.cpp
+++ b/Core/Compatibility.cpp
@@ -134,6 +134,7 @@ void Compatibility::CheckSettings(IniFile &iniFile, const std::string &gameID) {
 	CheckSetting(iniFile, gameID, "Fontltn12Hack", &flags_.Fontltn12Hack);
 	CheckSetting(iniFile, gameID, "LoadCLUTFromCurrentFrameOnly", &flags_.LoadCLUTFromCurrentFrameOnly);
 	CheckSetting(iniFile, gameID, "ForceUMDReadSpeed", &flags_.ForceUMDReadSpeed);
+	CheckSetting(iniFile, gameID, "AllowDelayedReadbacks", &flags_.AllowDelayedReadbacks);
 }
 
 void Compatibility::CheckVRSettings(IniFile &iniFile, const std::string &gameID) {
diff --git a/Core/Compatibility.h b/Core/Compatibility.h
index a917d17e5e..7cff655b0d 100644
--- a/Core/Compatibility.h
+++ b/Core/Compatibility.h
@@ -104,6 +104,7 @@ struct CompatFlags {
 	bool Fontltn12Hack;
 	bool LoadCLUTFromCurrentFrameOnly;
 	bool ForceUMDReadSpeed;
+	bool AllowDelayedReadbacks;
 };
 
 struct VRCompat {
diff --git a/GPU/Common/FramebufferManagerCommon.cpp b/GPU/Common/FramebufferManagerCommon.cpp
index e76c6ffa97..a3cdde39e8 100644
--- a/GPU/Common/FramebufferManagerCommon.cpp
+++ b/GPU/Common/FramebufferManagerCommon.cpp
@@ -2125,7 +2125,11 @@ bool FramebufferManagerCommon::NotifyFramebufferCopy(u32 src, u32 dst, int size,
 		if (srcH == 0 || srcY + srcH > srcBuffer->bufferHeight) {
 			WARN_LOG_ONCE(btdcpyheight, G3D, "Memcpy fbo download %08x -> %08x skipped, %d+%d is taller than %d", src, dst, srcY, srcH, srcBuffer->bufferHeight);
 		} else if (!g_Config.bSkipGPUReadbacks && (!srcBuffer->memoryUpdated || channel == RASTER_DEPTH)) {
-			ReadFramebufferToMemory(srcBuffer, 0, srcY, srcBuffer->width, srcH, channel, Draw::ReadbackMode::BLOCK);
+			Draw::ReadbackMode readbackMode = Draw::ReadbackMode::BLOCK;
+			if (PSP_CoreParameter().compat.flags().AllowDelayedReadbacks) {
+				readbackMode = Draw::ReadbackMode::OLD_DATA_OK;
+			}
+			ReadFramebufferToMemory(srcBuffer, 0, srcY, srcBuffer->width, srcH, channel, readbackMode);
 			srcBuffer->usageFlags = (srcBuffer->usageFlags | FB_USAGE_DOWNLOAD) & ~FB_USAGE_DOWNLOAD_CLEAR;
 		}
 		return false;
@@ -2649,7 +2653,11 @@ bool FramebufferManagerCommon::NotifyBlockTransferBefore(u32 dstBasePtr, int dst
 				if (tooTall) {
 					WARN_LOG_ONCE(btdheight, G3D, "Block transfer download %08x -> %08x dangerous, %d+%d is taller than %d", srcBasePtr, dstBasePtr, srcRect.y, srcRect.h, srcRect.vfb->bufferHeight);
 				}
-				ReadFramebufferToMemory(srcRect.vfb, static_cast<int>(srcX * srcXFactor), srcY, static_cast<int>(srcRect.w_bytes * srcXFactor), srcRect.h, RASTER_COLOR, Draw::ReadbackMode::BLOCK);
+				Draw::ReadbackMode readbackMode = Draw::ReadbackMode::BLOCK;
+				if (PSP_CoreParameter().compat.flags().AllowDelayedReadbacks) {
+					readbackMode = Draw::ReadbackMode::OLD_DATA_OK;
+				}
+				ReadFramebufferToMemory(srcRect.vfb, static_cast<int>(srcX * srcXFactor), srcY, static_cast<int>(srcRect.w_bytes * srcXFactor), srcRect.h, RASTER_COLOR, readbackMode);
 				srcRect.vfb->usageFlags = (srcRect.vfb->usageFlags | FB_USAGE_DOWNLOAD) & ~FB_USAGE_DOWNLOAD_CLEAR;
 			}
 		}
diff --git a/assets/compat.ini b/assets/compat.ini
index cac7e2377c..c0c1da77f0 100644
--- a/assets/compat.ini
+++ b/assets/compat.ini
@@ -1649,7 +1649,7 @@ NPEG90002 = true  # Demo
 SYPH04036 = true  # Prototype?
 
 [ForceUMDReadSpeed]
-# Aces of War required slow read speed (even in Real PSP) see #11062
+# Aces of War required slow read speed (even in Real PSP), see #11062
 ULES00590 = true
 ULJM05075 = true
 # Sengoku Musou 3Z Special DLC see #9993
@@ -1660,11 +1660,11 @@ ULJM06024 = true
 NPUG30038 = true
 NPEG00036 = true
 
-# Doko Demo Issho,load savedata error see #18420
+# Doko Demo Issho, load savedata error see #18420
 UCJS10002 = true
 UCJS18002 = true
 
-# Driver 76 ,see #16904 #12054
+# Driver 76, see #16904 #12054
 ULUS10235 = true
 ULES00740 = true
 
@@ -1682,3 +1682,9 @@ ULJS00290 = true
 ULKS46254 = true
 ULJS19057 = true
 NPJH50263 = true
+
+[AllowDelayedReadbacks]
+# NOTE: This only affects Vulkan currently.
+# Added for easy experimentation. Many games using readbacks do not work well delaying them, though.
+# For example, Motorstorm lighting adaptation goes into self-oscillation (!)
+# UCES01250 = true