/*
* gbe/gbe.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>
/* Size of gbe region in bytes */
#define GBEREGIONSIZE_8K 0x2000
/*
* 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)
* this function uses *word* not *byte* indexes, hence the bit shift.
*/
if (isBackup) offset = 0x1000>>1;
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_8K>>1];
memcpy(&gbeBuffer4k, &gbeStruct4k, GBEREGIONSIZE_8K>>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
* it so that the main region is usable.
*/
struct GBEREGIONRECORD_8K deblobbedGbeStruct8k;
memcpy(&deblobbedGbeStruct8k, &factoryGbeStruct8k, GBEREGIONSIZE_8K);
deblobbedGbeStruct8k.backup.checkSum = gbeGetChecksumFrom4kStruct(deblobbedGbeStruct8k.backup, 0xBABA);
memcpy(&deblobbedGbeStruct8k.main, &deblobbedGbeStruct8k.backup, GBEREGIONSIZE_8K>>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