Fixes a kernel panic when booting with the GPU enabled

AMDGPUWakeHandler.xcodeproj/xcuserdata/hugopires.xcuserdatad/xcschemes/AMDGPUWakeHandler.xcscheme

@@ -0,0 +1,82 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "0900"
+   version = "1.3">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "0C955B6D1FADF33500EFC963"
+               BuildableName = "AMDGPUWakeHandler.kext"
+               BlueprintName = "AMDGPUWakeHandler"
+               ReferencedContainer = "container:AMDGPUWakeHandler.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      language = ""
+      shouldUseLaunchSchemeArgsEnv = "YES">
+      <Testables>
+      </Testables>
+      <AdditionalOptions>
+      </AdditionalOptions>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      language = ""
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "0C955B6D1FADF33500EFC963"
+            BuildableName = "AMDGPUWakeHandler.kext"
+            BlueprintName = "AMDGPUWakeHandler"
+            ReferencedContainer = "container:AMDGPUWakeHandler.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+      <AdditionalOptions>
+      </AdditionalOptions>
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "0C955B6D1FADF33500EFC963"
+            BuildableName = "AMDGPUWakeHandler.kext"
+            BlueprintName = "AMDGPUWakeHandler"
+            ReferencedContainer = "container:AMDGPUWakeHandler.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>

AMDGPUWakeHandler/AMDGPUWakeHandler.cpp

@@ -1,17 +1,51 @@
+// Based on the linux implementationn of apple-gmux
+// https://github.com/torvalds/linux/blob/master/drivers/platform/x86/apple-gmux.c
 
 #include <IOKit/IOLib.h>
 #include "AMDGPUWakeHandler.hpp"
 
 #define kMyNumberOfStates 2
 #define kIOPMPowerOff 0
 
+#define GMUX_IOSTART                0x700
+
+#define GMUX_PORT_SWITCH_DISPLAY    0x10
+#define GMUX_PORT_SWITCH_DDC        0x28
+#define GMUX_PORT_SWITCH_EXTERNAL   0x40
+#define GMUX_PORT_DISCRETE_POWER    0x50
+
+#define GMUX_SWITCH_DDC_IGD         0x1
+#define GMUX_SWITCH_DISPLAY_IGD     0x2
+#define GMUX_SWITCH_EXTERNAL_IGD    0x2
+
+#define GMUX_DISCRETE_POWER_OFF     0x0
+
 // This required macro defines the class's constructors, destructors,
 // and several other methods I/O Kit requires.
 OSDefineMetaClassAndStructors(AMDGPUWakeHandler, IOService)
 
-static inline void outb(unsigned short port, unsigned char value)
+static inline void outb(uint16_t port, uint8_t value)
+{
+    asm volatile ("outb %0, %1" : : "a"(value), "Nd"(port));
+}
+
+static inline uint8_t inb(uint16_t port)
 {
-    __asm__ __volatile__ ("outb %1, %0" : : "dN" (port), "a" (value));
+    uint8_t ret;
+    asm volatile ("inb %1, %0" : "=a"(ret) : "Nd"(port));
+    return ret;
+}
+
+void gmux_write8(uint16_t port, uint8_t val) {
+    outb(GMUX_IOSTART + port, val);
+}
+
+uint8_t gmux_read8(unsigned short port) {
+    return inb(GMUX_IOSTART + port);
+}
+
+uint8_t get_discrete_state() {
+    return gmux_read8(GMUX_PORT_DISCRETE_POWER);
 }
 
 // Define the driver's superclass.
@@ -35,6 +69,10 @@ IOService *AMDGPUWakeHandler::probe(IOService *provider,
 {
     IOService *result = super::probe(provider, score);
     IOLog("Probing\n");
+    if (get_discrete_state() != 0) {
+        IOLog("Failed to Load. Discrete GPU was powered on\n");
+        return 0;
+    }
     return result;
 }
 
@@ -64,10 +102,10 @@ void AMDGPUWakeHandler::stop(IOService *provider)
 void AMDGPUWakeHandler::disableGPU()
 {
     IOLog("Disabling GPU\n");
-    outb(0x728, 0x1);
-    outb(0x710, 0x2);
-    outb(0x740, 0x2);
-    outb(0x750, 0x0);
+    gmux_write8(GMUX_PORT_SWITCH_DDC, GMUX_SWITCH_DDC_IGD);
+    gmux_write8(GMUX_PORT_SWITCH_DISPLAY, GMUX_SWITCH_DISPLAY_IGD);
+    gmux_write8(GMUX_PORT_SWITCH_EXTERNAL, GMUX_SWITCH_EXTERNAL_IGD);
+    gmux_write8(GMUX_PORT_DISCRETE_POWER, GMUX_DISCRETE_POWER_OFF);
 }
 
 IOReturn AMDGPUWakeHandler::setPowerState ( unsigned long whichState, IOService * whatDevice )

README.md

@@ -2,7 +2,7 @@
 
 This kernel extension disables the AMD GPU after waking up from sleep. It is intended to be used on a 2011 MacBook Pro with a failed AMD GPU.
 
-**NOTE: this should only be used with the grub solution ([found here](https://gist.github.com/blackgate/17ac402e35d2f7e0f1c9708db3dc7a44)) or similar that prevents the AMD kexts from being loaded, otherwise it will kernel panic.**
+**NOTE: this should only be used with the grub solution ([found here](https://gist.github.com/blackgate/17ac402e35d2f7e0f1c9708db3dc7a44)) or similar that powers down the discrete GPU before booting macOS, otherwise it will fail to load.**
 
 ## Installation