From 7ffd20ca3fc1e9d436683b2e34c4e2e47fac2c7f Mon Sep 17 00:00:00 2001
From: Francis Rowe <info@gluglug.org.uk>
Date: Tue, 23 Dec 2014 11:37:17 -0500
Subject: ich9deblob: move gbe functions to gbe/struct.h

---
(limited to 'resources/utilities/ich9deblob/gbe')

diff --git a/resources/utilities/ich9deblob/gbe/struct.h b/resources/utilities/ich9deblob/gbe/struct.h
index 294ff30..cbc2635 100644
--- a/resources/utilities/ich9deblob/gbe/struct.h
+++ b/resources/utilities/ich9deblob/gbe/struct.h
@@ -29,12 +29,19 @@
 #ifndef GBESTRUCT_H
 #define GBESTRUCT_H
 
+#include <stdio.h>
+#include <string.h>
+
 #define GBEREGIONSIZE 0x2000 // 8 KiB
 // These will have a modified descriptor+gbe based on what's in the factory.rom
 // These will be joined into a single 12KiB buffer (descriptor, then gbe) and saved to a file
 // NOTE: The GBE region of 8K is actually 2x 4K regions in a single region; both 4K blocks can be identical (and by default, are)
 // The 2nd one is a "backup", but we don't know when it's used. perhaps it's used when the checksum on the first one does not match?
 
+// ---------------------------------------------------------------------
+// Gbe struct representing the data
+// ---------------------------------------------------------------------
+
 struct GBEREGIONRECORD_4K {
 	unsigned char macAddress[6]; // 0x03 words, or 0x06 bytes
 	unsigned char otherStuff[120];  // 0x3c words, or 0x7E bytes
@@ -52,4 +59,70 @@ struct GBEREGIONRECORD_8K {
 	// lenovobios's gbe region) and then copy to main
 };
 
+// ---------------------------------------------------------------------
+// Gbe functions
+// ---------------------------------------------------------------------
+
+// Read a 16-bit unsigned int from a supplied region buffer
+unsigned short gbeGetRegionWordFrom8kBuffer(int index, char* regionData)
+{
+	return *((unsigned short*)(regionData + (index * 2)));
+}
+
+// checksum calculation for 8k gbe region (algorithm based on datasheet)
+// also works for 4k buffers, so long as isBackup remains false
+unsigned short gbeGetChecksumFrom8kBuffer(char* regionData, unsigned short desiredValue, char isBackup)
+{
+	int i;
+	
+	unsigned short regionWord; // store words here for adding to checksum
+	unsigned short checksum = 0; // this gbe's checksum
+	unsigned short offset = 0; // in bytes, from the start of the gbe region.
+	
+	// if isBackup is true, use 2nd gbe region ("backup" region)
+	if (isBackup) offset = 0x1000>>1; // this function uses *word* not *byte* indexes.
+
+	for (i = 0; i < 0x3F; i++) {
+		regionWord = gbeGetRegionWordFrom8kBuffer(i+offset, regionData);
+		checksum += regionWord;
+	}
+	checksum = desiredValue - checksum;
+	return checksum;
+}
+
+// checksum calculation for 4k gbe struct (algorithm based on datasheet)
+unsigned short gbeGetChecksumFrom4kStruct(struct GBEREGIONRECORD_4K gbeStruct4k, unsigned short desiredValue)
+{
+	char gbeBuffer4k[GBEREGIONSIZE>>1];
+	memcpy(&gbeBuffer4k, &gbeStruct4k, GBEREGIONSIZE>>1);
+	return gbeGetChecksumFrom8kBuffer(gbeBuffer4k, desiredValue, 0);
+}
+
+// modify the gbe region extracted from a factory.rom dump 
+struct GBEREGIONRECORD_8K deblobbedGbeStructFromFactory(struct GBEREGIONRECORD_8K factoryGbeStruct8k) 
+{	
+	// Correct the main gbe region. By default, the X200 (as shipped from Lenovo) comes
+	// with a broken main gbe region, where the backup gbe region is used instead. Modify
+	// the descriptor so that the main region is usable.
+	
+	struct GBEREGIONRECORD_8K deblobbedGbeStruct8k;
+	memcpy(&deblobbedGbeStruct8k, &factoryGbeStruct8k, GBEREGIONSIZE);
+	
+	deblobbedGbeStruct8k.backup.checkSum = gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.backup, 0xBABA);
+	memcpy(&deblobbedGbeStruct8k.main, &deblobbedGbeStruct8k.backup, GBEREGIONSIZE>>1);
+	
+	// Debugging:
+	// calculate the 0x3F'th 16-bit uint to make the desired final checksum for GBe
+	// observed checksum matches (from X200 factory.rom dumps) on main: 0x3ABA 0x34BA 0x40BA. spec defined as 0xBABA.
+	// X200 ships with a broken main gbe region by default (invalid checksum, and more)
+	// The "backup" gbe regions on these machines are correct, though, and is what the machines default to
+	// For libreboot's purpose, we can do much better than that by fixing the main one... below is only debugging
+	printf("\nfactory Gbe (main): calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(factoryGbeStruct8k.main, 0xBABA), factoryGbeStruct8k.main.checkSum);
+	printf("factory Gbe (backup) calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(factoryGbeStruct8k.backup, 0xBABA), factoryGbeStruct8k.backup.checkSum);
+	printf("\ndeblobbed Gbe (main): calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.main, 0xBABA), deblobbedGbeStruct8k.main.checkSum);
+	printf("deblobbed Gbe (backup) calculated Gbe checksum: 0x%hx and actual GBe checksum: 0x%hx\n", gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.backup, 0xBABA), deblobbedGbeStruct8k.backup.checkSum);
+	
+	return deblobbedGbeStruct8k;
+}
+
 #endif
--
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