/*
 *  gbe/struct.h
 *  This file is part of the ich9deblob utility from the libreboot project
 *
 *  Copyright (C) 2014 Steve Shenton <sgsit@libreboot.org>
 *                     Francis Rowe <info@gluglug.org.uk>
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
// Purpose: provide struct representing gbe region.
// Map actual buffers of this regions, directly to instances of these
// structs. This makes working with gbe really easy.
 
// bit fields used, corresponding to datasheet. See links to datasheets
// and documentation in ich9deblob.c

#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
	unsigned short checkSum; // when added to the sum of all words above, this should be 0xBABA
	unsigned char padding1[3968];
};

// main and backup region in gbe
struct GBEREGIONRECORD_8K {
	struct GBEREGIONRECORD_4K main;
	struct GBEREGIONRECORD_4K backup;
	// Backup region:
	// This is actually "main" on X200, since the real main has a bad checksum
	// and other errors. You should do what you need on this one (if modifying
	// 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