// SPDX-License-Identifier: GPL-2.0-or-later
/*
    Retrieve encoded MAC address from 24C16 serial 2-wire EEPROM,
    decode it and store it in the associated adapter struct for
    use by dvb_net.c

    This card appear to have the 24C16 write protect held to ground,
    thus permitting normal read/write operation. Theoretically it
    would be possible to write routines to burn a different (encoded)
    MAC address into the EEPROM.

    Robert Schlabbach   GMX
    Michael Glaum       KVH Industries
    Holger Waechtler    Convergence

    Copyright (C) 2002-2003 Ralph Metzler <rjkm@metzlerbros.de>
                            Metzler Brothers Systementwicklung GbR


*/

#include <asm/errno.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/i2c.h>
#include <linux/etherdevice.h>

#include "ttpci-eeprom.h"

#if 1
#define dprintk(x...) do { printk(x); } while (0)
#else
#define dprintk(x...) do { } while (0)
#endif


static int check_mac_tt(u8 *buf)
{
        int i;
        u16 tmp = 0xffff;

        for (i = 0; i < 8; i++) {
                tmp  = (tmp << 8) | ((tmp >> 8) ^ buf[i]);
                tmp ^= (tmp >> 4) & 0x0f;
                tmp ^= (tmp << 12) ^ ((tmp & 0xff) << 5);
        }
        tmp ^= 0xffff;
        return (((tmp >> 8) ^ buf[8]) | ((tmp & 0xff) ^ buf[9]));
}

static int getmac_tt(u8 * decodedMAC, u8 * encodedMAC)
{
        u8 xor[20] = { 0x72, 0x23, 0x68, 0x19, 0x5c, 0xa8, 0x71, 0x2c,
                       0x54, 0xd3, 0x7b, 0xf1, 0x9E, 0x23, 0x16, 0xf6,
                       0x1d, 0x36, 0x64, 0x78};
        u8 data[20];
        int i;

        /* In case there is a sig check failure have the orig contents available */
        memcpy(data, encodedMAC, 20);

        for (i = 0; i < 20; i++)
                data[i] ^= xor[i];
        for (i = 0; i < 10; i++)
                data[i] = ((data[2 * i + 1] << 8) | data[2 * i])
                        >> ((data[2 * i + 1] >> 6) & 3);

        if (check_mac_tt(data))
                return -ENODEV;

        decodedMAC[0] = data[2]; decodedMAC[1] = data[1]; decodedMAC[2] = data[0];
        decodedMAC[3] = data[6]; decodedMAC[4] = data[5]; decodedMAC[5] = data[4];
        return 0;
}

int ttpci_eeprom_decode_mac(u8 *decodedMAC, u8 *encodedMAC)
{
        u8 xor[20] = { 0x72, 0x23, 0x68, 0x19, 0x5c, 0xa8, 0x71, 0x2c,
                       0x54, 0xd3, 0x7b, 0xf1, 0x9E, 0x23, 0x16, 0xf6,
                       0x1d, 0x36, 0x64, 0x78};
        u8 data[20];
        int i;

        memcpy(data, encodedMAC, 20);

        for (i = 0; i < 20; i++)
                data[i] ^= xor[i];
        for (i = 0; i < 10; i++)
                data[i] = ((data[2 * i + 1] << 8) | data[2 * i])
                        >> ((data[2 * i + 1] >> 6) & 3);

        if (check_mac_tt(data))
                return -ENODEV;

        decodedMAC[0] = data[2];
        decodedMAC[1] = data[1];
        decodedMAC[2] = data[0];
        decodedMAC[3] = data[6];
        decodedMAC[4] = data[5];
        decodedMAC[5] = data[4];
        return 0;
}
EXPORT_SYMBOL(ttpci_eeprom_decode_mac);

static int ttpci_eeprom_read_encodedMAC(struct i2c_adapter *adapter, u8 * encodedMAC)
{
        int ret;
        u8 b0[] = { 0xcc };

        struct i2c_msg msg[] = {
                { .addr = 0x50, .flags = 0, .buf = b0, .len = 1 },
                { .addr = 0x50, .flags = I2C_M_RD, .buf = encodedMAC, .len = 20 }
        };

        /* dprintk("%s\n", __func__); */

        ret = i2c_transfer(adapter, msg, 2);

        if (ret != 2)           /* Assume EEPROM isn't there */
                return (-ENODEV);

        return 0;
}


int ttpci_eeprom_parse_mac(struct i2c_adapter *adapter, u8 *proposed_mac)
{
        int ret;
        u8 encodedMAC[20];
        u8 decodedMAC[6];

        ret = ttpci_eeprom_read_encodedMAC(adapter, encodedMAC);

        if (ret != 0) {         /* Will only be -ENODEV */
                dprintk("Couldn't read from EEPROM: not there?\n");
                eth_zero_addr(proposed_mac);
                return ret;
        }

        ret = getmac_tt(decodedMAC, encodedMAC);
        if( ret != 0 ) {
                dprintk("adapter failed MAC signature check\n");
                dprintk("encoded MAC from EEPROM was %*phC",
                        (int)sizeof(encodedMAC), &encodedMAC);
                eth_zero_addr(proposed_mac);
                return ret;
        }

        memcpy(proposed_mac, decodedMAC, 6);
        dprintk("adapter has MAC addr = %pM\n", decodedMAC);
        return 0;
}

EXPORT_SYMBOL(ttpci_eeprom_parse_mac);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Ralph Metzler, Marcus Metzler, others");
MODULE_DESCRIPTION("Decode dvb_net MAC address from EEPROM of PCI DVB cards made by Siemens, Technotrend, Hauppauge");