Detect and add keyboard input workaround for early AMI UEFI v2.0 systems

* Early AMI UEFI v2.0 firmwares, such as the ones found in Dell Optiplex 390s,
  are unable to process USB keyboard input when the USB bus is simultaneously
  being used to read data at high speed.
* To work around this, we need to stall the system at regular intervals, so
  that it gets a chance to process USB keyboard cancellation.
* A 5 ms delay for each 1 MB read appears to be enough (and should only add
  about 5 seconds extra time for each GB of data being read).

src/boot.c

@@ -28,6 +28,12 @@ EFI_HANDLE gMainImageHandle = NULL;
  */
 BOOLEAN gIsTestMode = FALSE;
 
+/*
+ * Amount of time to pause after a read, in order to give buggy UEFI
+ * firmwares enough time to process USB keyboard input (in μs).
+ */
+UINTN gPauseAfterRead = 0;
+
 /* Strings used for platform identification */
 #if defined(_M_X64) || defined(__x86_64__)
 STATIC CHAR16* Arch = L"x64";
@@ -316,6 +322,13 @@ EFI_STATUS EFIAPI efi_main(
 		goto out;
 	}
 
+	// Detect if we are booting on an early AMI UEFI v2.0 system
+	if (IsEarlyAmiUefi()) {
+		PrintWarning(L"Early AMI UEFI firmware detected!");
+		PrintWarning(L"This system may have trouble processing keyboard input.");
+		gPauseAfterRead = 5000;
+	}
+
 	// Detect if we are booting from an NTFS partition served by the buggy
 	// AMI NTFS driver and alert the user if that is the case.
 	if (IsProblematicNtfsDriver(DeviceHandle)) {

src/boot.h

@@ -71,6 +71,9 @@ extern EFI_HANDLE           gMainImageHandle;
 /* Set to true when we are running the GitHub Actions tests */
 extern BOOLEAN              gIsTestMode;
 
+/* Amount of time to pause after a read (in μs) */
+extern UINTN                gPauseAfterRead;
+
 /* Dimensions of the UEFI text console */
 typedef struct {
 	UINTN Cols;
@@ -378,6 +381,15 @@ STATIC __inline VOID _SafeStrCat(CHAR16* Destination, UINTN DestMax,
 **/
 BOOLEAN IsTestSystem(VOID);
 
+/**
+  Detect if we are running an early AMI UEFI v2.0 system, that can't process USB
+  keyboard inputs unless we give it time to breathe.
+
+  @retval TRUE   An AMI v2.0 UEFI firmware was detected.
+  @retval FALSE  The system is not AMI v2.0 UEFI.
+**/
+BOOLEAN IsEarlyAmiUefi(VOID);
+
 /**
   Detect if we are running of an NTFS partition with the buggy AMI NTFS file system
   driver (See: https://github.com/pbatard/AmiNtfsBug)

src/hash.c

@@ -340,6 +340,13 @@ EFI_STATUS HashFile(
 	for (ReadBytes = 0; ; ReadBytes += ReadSize) {
 		ReadSize = READ_BUFFERSIZE;
 		Status = File->Read(File, &ReadSize, Buffer);
+		// Early AMI UEFI v2.0 firmwares, such as the ones found in Dell
+		// Optiplex 390s, are unable to process USB keyboard input when
+		// the USB bus is simultaneously used to read data at high speed.
+		// So we pause these systems, to give them enough time to "breathe"
+		// and process USB keyboard cancellation.
+		if (gPauseAfterRead != 0)
+			Sleep(gPauseAfterRead);
 		if (EFI_ERROR(Status))
 			goto out;
 		if (ReadSize == 0)

src/system.c

@@ -1,6 +1,6 @@
 /*
  * uefi-md5sum: UEFI MD5Sum validator - System Information
- * Copyright © 2014-2023 Pete Batard <pete@akeo.ie>
+ * Copyright © 2014-2024 Pete Batard <pete@akeo.ie>
  * With parts from EDK © 1998  Intel Corporation
  *
  * This program is free software: you can redistribute it and/or modify
@@ -142,6 +142,19 @@ BOOLEAN IsTestSystem(VOID)
 	return FALSE;
 }
 
+/**
+  Detect if we are running an early AMI UEFI v2.0 system, that can't
+  process USB keyboard inputs unless we give it time to breathe.
+
+  @retval TRUE   An AMI v2.0 UEFI firmware was detected.
+  @retval FALSE  The system is not AMI v2.0 UEFI.
+**/
+BOOLEAN IsEarlyAmiUefi(VOID)
+{
+	return (StrCmp(gST->FirmwareVendor, L"American Megatrends") == 0 &&
+		gST->Hdr.Revision == 0x20000);
+}
+
 /**
   Return a driver name from a driver handle.
   Note that this call does not attempt to resolve the name of drivers