cmd_i2c.c

/*
 * (C) Copyright 2009
 * Sergey Kubushyn, himself, ksi@koi8.net
 *
 * Changes for unified multibus/multiadapter I2C support.
 *
 * (C) Copyright 2001
 * Gerald Van Baren, Custom IDEAS, vanbaren@cideas.com.
 *
 * SPDX-License-Identifier:	GPL-2.0+
 */

/*
 * I2C Functions similar to the standard memory functions.
 *
 * There are several parameters in many of the commands that bear further
 * explanations:
 *
 * {i2c_chip} is the I2C chip address (the first byte sent on the bus).
 *   Each I2C chip on the bus has a unique address.  On the I2C data bus,
 *   the address is the upper seven bits and the LSB is the "read/write"
 *   bit.  Note that the {i2c_chip} address specified on the command
 *   line is not shifted up: e.g. a typical EEPROM memory chip may have
 *   an I2C address of 0x50, but the data put on the bus will be 0xA0
 *   for write and 0xA1 for read.  This "non shifted" address notation
 *   matches at least half of the data sheets :-/.
 *
 * {addr} is the address (or offset) within the chip.  Small memory
 *   chips have 8 bit addresses.  Large memory chips have 16 bit
 *   addresses.  Other memory chips have 9, 10, or 11 bit addresses.
 *   Many non-memory chips have multiple registers and {addr} is used
 *   as the register index.  Some non-memory chips have only one register
 *   and therefore don't need any {addr} parameter.
 *
 *   The default {addr} parameter is one byte (.1) which works well for
 *   memories and registers with 8 bits of address space.
 *
 *   You can specify the length of the {addr} field with the optional .0,
 *   .1, or .2 modifier (similar to the .b, .w, .l modifier).  If you are
 *   manipulating a single register device which doesn't use an address
 *   field, use "0.0" for the address and the ".0" length field will
 *   suppress the address in the I2C data stream.  This also works for
 *   successive reads using the I2C auto-incrementing memory pointer.
 *
 *   If you are manipulating a large memory with 2-byte addresses, use
 *   the .2 address modifier, e.g. 210.2 addresses location 528 (decimal).
 *
 *   Then there are the unfortunate memory chips that spill the most
 *   significant 1, 2, or 3 bits of address into the chip address byte.
 *   This effectively makes one chip (logically) look like 2, 4, or
 *   8 chips.  This is handled (awkwardly) by #defining
 *   CONFIG_SYS_I2C_EEPROM_ADDR_OVERFLOW and using the .1 modifier on the
 *   {addr} field (since .1 is the default, it doesn't actually have to
 *   be specified).  Examples: given a memory chip at I2C chip address
 *   0x50, the following would happen...
 *     i2c md 50 0 10   display 16 bytes starting at 0x000
 *                      On the bus: <S> A0 00 <E> <S> A1 <rd> ... <rd>
 *     i2c md 50 100 10 display 16 bytes starting at 0x100
 *                      On the bus: <S> A2 00 <E> <S> A3 <rd> ... <rd>
 *     i2c md 50 210 10 display 16 bytes starting at 0x210
 *                      On the bus: <S> A4 10 <E> <S> A5 <rd> ... <rd>
 *   This is awfully ugly.  It would be nice if someone would think up
 *   a better way of handling this.
 *
 * Adapted from cmd_mem.c which is copyright Wolfgang Denk (wd@denx.de).
 */

#include <common.h>
#include <bootretry.h>
#include <cli.h>
#include <command.h>
#include <edid.h>
#include <environment.h>
#include <i2c.h>
#include <malloc.h>
#include <asm/byteorder.h>
#include <linux/compiler.h>

DECLARE_GLOBAL_DATA_PTR;

/* Display values from last command.
 * Memory modify remembered values are different from display memory.
 */
static uchar	i2c_dp_last_chip;
static uint	i2c_dp_last_addr;
static uint	i2c_dp_last_alen;
static uint	i2c_dp_last_length = 0x10;

static uchar	i2c_mm_last_chip;
static uint	i2c_mm_last_addr;
static uint	i2c_mm_last_alen;

/* If only one I2C bus is present, the list of devices to ignore when
 * the probe command is issued is represented by a 1D array of addresses.
 * When multiple buses are present, the list is an array of bus-address
 * pairs.  The following macros take care of this */

#if defined(CONFIG_SYS_I2C_NOPROBES)
#if defined(CONFIG_SYS_I2C) || defined(CONFIG_I2C_MULTI_BUS)
static struct
{
	uchar	bus;
	uchar	addr;
} i2c_no_probes[] = CONFIG_SYS_I2C_NOPROBES;
#define GET_BUS_NUM	i2c_get_bus_num()
#define COMPARE_BUS(b,i)	(i2c_no_probes[(i)].bus == (b))
#define COMPARE_ADDR(a,i)	(i2c_no_probes[(i)].addr == (a))
#define NO_PROBE_ADDR(i)	i2c_no_probes[(i)].addr
#else		/* single bus */
static uchar i2c_no_probes[] = CONFIG_SYS_I2C_NOPROBES;
#define GET_BUS_NUM	0
#define COMPARE_BUS(b,i)	((b) == 0)	/* Make compiler happy */
#define COMPARE_ADDR(a,i)	(i2c_no_probes[(i)] == (a))
#define NO_PROBE_ADDR(i)	i2c_no_probes[(i)]
#endif	/* defined(CONFIG_SYS_I2C) */
#endif

#define DISP_LINE_LEN	16

/**
 * i2c_init_board() - Board-specific I2C bus init
 *
 * This function is the default no-op implementation of I2C bus
 * initialization. This function can be overriden by board-specific
 * implementation if needed.
 */
__weak
void i2c_init_board(void)
{
}

/* TODO: Implement architecture-specific get/set functions */

/**
 * i2c_get_bus_speed() - Return I2C bus speed
 *
 * This function is the default implementation of function for retrieveing
 * the current I2C bus speed in Hz.
 *
 * A driver implementing runtime switching of I2C bus speed must override
 * this function to report the speed correctly. Simple or legacy drivers
 * can use this fallback.
 *
 * Returns I2C bus speed in Hz.
 */
#if !defined(CONFIG_SYS_I2C)
/*
 * TODO: Implement architecture-specific get/set functions
 * Should go away, if we switched completely to new multibus support
 */
__weak
unsigned int i2c_get_bus_speed(void)
{
	return CONFIG_SYS_I2C_SPEED;
}

/**
 * i2c_set_bus_speed() - Configure I2C bus speed
 * @speed:	Newly set speed of the I2C bus in Hz
 *
 * This function is the default implementation of function for setting
 * the I2C bus speed in Hz.
 *
 * A driver implementing runtime switching of I2C bus speed must override
 * this function to report the speed correctly. Simple or legacy drivers
 * can use this fallback.
 *
 * Returns zero on success, negative value on error.
 */
__weak
int i2c_set_bus_speed(unsigned int speed)
{
	if (speed != CONFIG_SYS_I2C_SPEED)
		return -1;

	return 0;
}
#endif

/**
 * get_alen() - Small parser helper function to get address length
 *
 * Returns the address length.
 */
static uint get_alen(char *arg)
{
	int	j;
	int	alen;

	alen = 1;
	for (j = 0; j < 8; j++) {
		if (arg[j] == '.') {
			alen = arg[j+1] - '0';
			break;
		} else if (arg[j] == '\0')
			break;
	}
	return alen;
}

/**
 * do_i2c_read() - Handle the "i2c read" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c read {i2c_chip} {devaddr}{.0, .1, .2} {len} {memaddr}
 */
static int do_i2c_read ( cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	u_char	chip;
	uint	devaddr, alen, length;
	u_char  *memaddr;

	if (argc != 5)
		return CMD_RET_USAGE;

	/*
	 * I2C chip address
	 */
	chip = simple_strtoul(argv[1], NULL, 16);

	/*
	 * I2C data address within the chip.  This can be 1 or
	 * 2 bytes long.  Some day it might be 3 bytes long :-).
	 */
	devaddr = simple_strtoul(argv[2], NULL, 16);
	alen = get_alen(argv[2]);
	if (alen > 3)
		return CMD_RET_USAGE;

	/*
	 * Length is the number of objects, not number of bytes.
	 */
	length = simple_strtoul(argv[3], NULL, 16);

	/*
	 * memaddr is the address where to store things in memory
	 */
	memaddr = (u_char *)simple_strtoul(argv[4], NULL, 16);

	if (i2c_read(chip, devaddr, alen, memaddr, length) != 0) {
		puts ("Error reading the chip.\n");
		return 1;
	}
	return 0;
}

static int do_i2c_write(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	u_char	chip;
	uint	devaddr, alen, length;
	u_char  *memaddr;

	if (argc != 5)
		return cmd_usage(cmdtp);

	/*
	 * memaddr is the address where to store things in memory
	 */
	memaddr = (u_char *)simple_strtoul(argv[1], NULL, 16);

	/*
	 * I2C chip address
	 */
	chip = simple_strtoul(argv[2], NULL, 16);

	/*
	 * I2C data address within the chip.  This can be 1 or
	 * 2 bytes long.  Some day it might be 3 bytes long :-).
	 */
	devaddr = simple_strtoul(argv[3], NULL, 16);
	alen = get_alen(argv[3]);
	if (alen > 3)
		return cmd_usage(cmdtp);

	/*
	 * Length is the number of objects, not number of bytes.
	 */
	length = simple_strtoul(argv[4], NULL, 16);

	while (length-- > 0) {
		if (i2c_write(chip, devaddr++, alen, memaddr++, 1) != 0) {
			puts("Error writing to the chip.\n");
			return 1;
		}
/*
 * No write delay with FRAM devices.
 */
#if !defined(CONFIG_SYS_I2C_FRAM)
		udelay(11000);
#endif
	}
	return 0;
}

/**
 * do_i2c_md() - Handle the "i2c md" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c md {i2c_chip} {addr}{.0, .1, .2} {len}
 */
static int do_i2c_md ( cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	u_char	chip;
	uint	addr, alen, length;
	int	j, nbytes, linebytes;

	/* We use the last specified parameters, unless new ones are
	 * entered.
	 */
	chip   = i2c_dp_last_chip;
	addr   = i2c_dp_last_addr;
	alen   = i2c_dp_last_alen;
	length = i2c_dp_last_length;

	if (argc < 3)
		return CMD_RET_USAGE;

	if ((flag & CMD_FLAG_REPEAT) == 0) {
		/*
		 * New command specified.
		 */

		/*
		 * I2C chip address
		 */
		chip = simple_strtoul(argv[1], NULL, 16);

		/*
		 * I2C data address within the chip.  This can be 1 or
		 * 2 bytes long.  Some day it might be 3 bytes long :-).
		 */
		addr = simple_strtoul(argv[2], NULL, 16);
		alen = get_alen(argv[2]);
		if (alen > 3)
			return CMD_RET_USAGE;

		/*
		 * If another parameter, it is the length to display.
		 * Length is the number of objects, not number of bytes.
		 */
		if (argc > 3)
			length = simple_strtoul(argv[3], NULL, 16);
	}

	/*
	 * Print the lines.
	 *
	 * We buffer all read data, so we can make sure data is read only
	 * once.
	 */
	nbytes = length;
	do {
		unsigned char	linebuf[DISP_LINE_LEN];
		unsigned char	*cp;

		linebytes = (nbytes > DISP_LINE_LEN) ? DISP_LINE_LEN : nbytes;

		if (i2c_read(chip, addr, alen, linebuf, linebytes) != 0)
			puts ("Error reading the chip.\n");
		else {
			printf("%04x:", addr);
			cp = linebuf;
			for (j=0; j<linebytes; j++) {
				printf(" %02x", *cp++);
				addr++;
			}
			puts ("    ");
			cp = linebuf;
			for (j=0; j<linebytes; j++) {
				if ((*cp < 0x20) || (*cp > 0x7e))
					puts (".");
				else
					printf("%c", *cp);
				cp++;
			}
			putc ('\n');
		}
		nbytes -= linebytes;
	} while (nbytes > 0);

	i2c_dp_last_chip   = chip;
	i2c_dp_last_addr   = addr;
	i2c_dp_last_alen   = alen;
	i2c_dp_last_length = length;

	return 0;
}

/**
 * do_i2c_mw() - Handle the "i2c mw" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c mw {i2c_chip} {addr}{.0, .1, .2} {data} [{count}]
 */
static int do_i2c_mw ( cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	uchar	chip;
	ulong	addr;
	uint	alen;
	uchar	byte;
	int	count;

	if ((argc < 4) || (argc > 5))
		return CMD_RET_USAGE;

	/*
	 * Chip is always specified.
	 */
	chip = simple_strtoul(argv[1], NULL, 16);

	/*
	 * Address is always specified.
	 */
	addr = simple_strtoul(argv[2], NULL, 16);
	alen = get_alen(argv[2]);
	if (alen > 3)
		return CMD_RET_USAGE;

	/*
	 * Value to write is always specified.
	 */
	byte = simple_strtoul(argv[3], NULL, 16);

	/*
	 * Optional count
	 */
	if (argc == 5)
		count = simple_strtoul(argv[4], NULL, 16);
	else
		count = 1;

	while (count-- > 0) {
		if (i2c_write(chip, addr++, alen, &byte, 1) != 0)
			puts ("Error writing the chip.\n");
		/*
		 * Wait for the write to complete.  The write can take
		 * up to 10mSec (we allow a little more time).
		 */
/*
 * No write delay with FRAM devices.
 */
#if !defined(CONFIG_SYS_I2C_FRAM)
		udelay(11000);
#endif
	}

	return 0;
}

/**
 * do_i2c_crc() - Handle the "i2c crc32" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Calculate a CRC on memory
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c crc32 {i2c_chip} {addr}{.0, .1, .2} {count}
 */
static int do_i2c_crc (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	uchar	chip;
	ulong	addr;
	uint	alen;
	int	count;
	uchar	byte;
	ulong	crc;
	ulong	err;

	if (argc < 4)
		return CMD_RET_USAGE;

	/*
	 * Chip is always specified.
	 */
	chip = simple_strtoul(argv[1], NULL, 16);

	/*
	 * Address is always specified.
	 */
	addr = simple_strtoul(argv[2], NULL, 16);
	alen = get_alen(argv[2]);
	if (alen > 3)
		return CMD_RET_USAGE;

	/*
	 * Count is always specified
	 */
	count = simple_strtoul(argv[3], NULL, 16);

	printf ("CRC32 for %08lx ... %08lx ==> ", addr, addr + count - 1);
	/*
	 * CRC a byte at a time.  This is going to be slooow, but hey, the
	 * memories are small and slow too so hopefully nobody notices.
	 */
	crc = 0;
	err = 0;
	while (count-- > 0) {
		if (i2c_read(chip, addr, alen, &byte, 1) != 0)
			err++;
		crc = crc32 (crc, &byte, 1);
		addr++;
	}
	if (err > 0)
		puts ("Error reading the chip,\n");
	else
		printf ("%08lx\n", crc);

	return 0;
}

/**
 * mod_i2c_mem() - Handle the "i2c mm" and "i2c nm" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Modify memory.
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c mm{.b, .w, .l} {i2c_chip} {addr}{.0, .1, .2}
 *	i2c nm{.b, .w, .l} {i2c_chip} {addr}{.0, .1, .2}
 */
static int
mod_i2c_mem(cmd_tbl_t *cmdtp, int incrflag, int flag, int argc, char * const argv[])
{
	uchar	chip;
	ulong	addr;
	uint	alen;
	ulong	data;
	int	size = 1;
	int	nbytes;

	if (argc != 3)
		return CMD_RET_USAGE;

	bootretry_reset_cmd_timeout();	/* got a good command to get here */
	/*
	 * We use the last specified parameters, unless new ones are
	 * entered.
	 */
	chip = i2c_mm_last_chip;
	addr = i2c_mm_last_addr;
	alen = i2c_mm_last_alen;

	if ((flag & CMD_FLAG_REPEAT) == 0) {
		/*
		 * New command specified.  Check for a size specification.
		 * Defaults to byte if no or incorrect specification.
		 */
		size = cmd_get_data_size(argv[0], 1);

		/*
		 * Chip is always specified.
		 */
		chip = simple_strtoul(argv[1], NULL, 16);

		/*
		 * Address is always specified.
		 */
		addr = simple_strtoul(argv[2], NULL, 16);
		alen = get_alen(argv[2]);
		if (alen > 3)
			return CMD_RET_USAGE;
	}

	/*
	 * Print the address, followed by value.  Then accept input for
	 * the next value.  A non-converted value exits.
	 */
	do {
		printf("%08lx:", addr);
		if (i2c_read(chip, addr, alen, (uchar *)&data, size) != 0)
			puts ("\nError reading the chip,\n");
		else {
			data = cpu_to_be32(data);
			if (size == 1)
				printf(" %02lx", (data >> 24) & 0x000000FF);
			else if (size == 2)
				printf(" %04lx", (data >> 16) & 0x0000FFFF);
			else
				printf(" %08lx", data);
		}

		nbytes = cli_readline(" ? ");
		if (nbytes == 0) {
			/*
			 * <CR> pressed as only input, don't modify current
			 * location and move to next.
			 */
			if (incrflag)
				addr += size;
			nbytes = size;
			/* good enough to not time out */
			bootretry_reset_cmd_timeout();
		}
#ifdef CONFIG_BOOT_RETRY_TIME
		else if (nbytes == -2)
			break;	/* timed out, exit the command	*/
#endif
		else {
			char *endp;

			data = simple_strtoul(console_buffer, &endp, 16);
			if (size == 1)
				data = data << 24;
			else if (size == 2)
				data = data << 16;
			data = be32_to_cpu(data);
			nbytes = endp - console_buffer;
			if (nbytes) {
				/*
				 * good enough to not time out
				 */
				bootretry_reset_cmd_timeout();
				if (i2c_write(chip, addr, alen, (uchar *)&data, size) != 0)
					puts ("Error writing the chip.\n");
#ifdef CONFIG_SYS_EEPROM_PAGE_WRITE_DELAY_MS
				udelay(CONFIG_SYS_EEPROM_PAGE_WRITE_DELAY_MS * 1000);
#endif
				if (incrflag)
					addr += size;
			}
		}
	} while (nbytes);

	i2c_mm_last_chip = chip;
	i2c_mm_last_addr = addr;
	i2c_mm_last_alen = alen;

	return 0;
}

/**
 * do_i2c_probe() - Handle the "i2c probe" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c probe {addr}
 *
 * Returns zero (success) if one or more I2C devices was found
 */
static int do_i2c_probe (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	int j;
	int addr = -1;
	int found = 0;
#if defined(CONFIG_SYS_I2C_NOPROBES)
	int k, skip;
	unsigned int bus = GET_BUS_NUM;
#endif	/* NOPROBES */

	if (argc == 2)
		addr = simple_strtol(argv[1], 0, 16);

	puts ("Valid chip addresses:");
	for (j = 0; j < 128; j++) {
		if ((0 <= addr) && (j != addr))
			continue;

#if defined(CONFIG_SYS_I2C_NOPROBES)
		skip = 0;
		for (k = 0; k < ARRAY_SIZE(i2c_no_probes); k++) {
			if (COMPARE_BUS(bus, k) && COMPARE_ADDR(j, k)) {
				skip = 1;
				break;
			}
		}
		if (skip)
			continue;
#endif
		if (i2c_probe(j) == 0) {
			printf(" %02X", j);
			found++;
		}
	}
	putc ('\n');

#if defined(CONFIG_SYS_I2C_NOPROBES)
	puts ("Excluded chip addresses:");
	for (k = 0; k < ARRAY_SIZE(i2c_no_probes); k++) {
		if (COMPARE_BUS(bus,k))
			printf(" %02X", NO_PROBE_ADDR(k));
	}
	putc ('\n');
#endif

	return (0 == found);
}

/**
 * do_i2c_loop() - Handle the "i2c loop" command-line command
 * @cmdtp:	Command data struct pointer
 * @flag:	Command flag
 * @argc:	Command-line argument count
 * @argv:	Array of command-line arguments
 *
 * Returns zero on success, CMD_RET_USAGE in case of misuse and negative
 * on error.
 *
 * Syntax:
 *	i2c loop {i2c_chip} {addr}{.0, .1, .2} [{length}] [{delay}]
 *	{length} - Number of bytes to read
 *	{delay}  - A DECIMAL number and defaults to 1000 uSec
 */
static int do_i2c_loop(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	u_char	chip;
	ulong	alen;
	uint	addr;
	uint	length;
	u_char	bytes[16];
	int	delay;

	if (argc < 3)
		return CMD_RET_USAGE;

	/*
	 * Chip is always specified.
	 */
	chip = simple_strtoul(argv[1], NULL, 16);

	/*
	 * Address is always specified.
	 */
	addr = simple_strtoul(argv[2], NULL, 16);
	alen = get_alen(argv[2]);
	if (alen > 3)
		return CMD_RET_USAGE;

	/*
	 * Length is the number of objects, not number of bytes.
	 */
	length = 1;
	length = simple_strtoul(argv[3], NULL, 16);
	if (length > sizeof(bytes))
		length = sizeof(bytes);

	/*
	 * The delay time (uSec) is optional.
	 */
	delay = 1000;
	if (argc > 3)
		delay = simple_strtoul(argv[4], NULL, 10);
	/*
	 * Run the loop...
	 */
	while (1) {
		if (i2c_read(chip, addr, alen, bytes, length) != 0)
			puts ("Error reading the chip.\n");
		udelay(delay);
	}

	/* NOTREACHED */
	return 0;
}

/*
 * The SDRAM command is separately configured because many
 * (most?) embedded boards don't use SDRAM DIMMs.
 *
 * FIXME: Document and probably move elsewhere!
 */
#if defined(CONFIG_CMD_SDRAM)
static void print_ddr2_tcyc (u_char const b)
{
	printf ("%d.", (b >> 4) & 0x0F);
	switch (b & 0x0F) {
	case 0x0:
	case 0x1:
	case 0x2:
	case 0x3:
	case 0x4:
	case 0x5:
	case 0x6:
	case 0x7:
	case 0x8:
	case 0x9:
		printf ("%d ns\n", b & 0x0F);
		break;
	case 0xA:
		puts ("25 ns\n");
		break;
	case 0xB:
		puts ("33 ns\n");
		break;
	case 0xC:
		puts ("66 ns\n");
		break;
	case 0xD:
		puts ("75 ns\n");
		break;
	default:
		puts ("?? ns\n");
		break;
	}
}

static void decode_bits (u_char const b, char const *str[], int const do_once)
{
	u_char mask;

	for (mask = 0x80; mask != 0x00; mask >>= 1, ++str) {
		if (b & mask) {
			puts (*str);
			if (do_once)
				return;
		}
	}
}

/*
 * Syntax:
 *	i2c sdram {i2c_chip}
 */
static int do_sdram (cmd_tbl_t * cmdtp, int flag, int argc, char * const argv[])
{
	enum { unknown, EDO, SDRAM, DDR2 } type;

	u_char	chip;
	u_char	data[128];
	u_char	cksum;
	int	j;

	static const char *decode_CAS_DDR2[] = {
		" TBD", " 6", " 5", " 4", " 3", " 2", " TBD", " TBD"
	};

	static const char *decode_CAS_default[] = {
		" TBD", " 7", " 6", " 5", " 4", " 3", " 2", " 1"
	};

	static const char *decode_CS_WE_default[] = {
		" TBD", " 6", " 5", " 4", " 3", " 2", " 1", " 0"
	};

	static const char *decode_byte21_default[] = {
		"  TBD (bit 7)\n",
		"  Redundant row address\n",
		"  Differential clock input\n",
		"  Registerd DQMB inputs\n",
		"  Buffered DQMB inputs\n",
		"  On-card PLL\n",
		"  Registered address/control lines\n",
		"  Buffered address/control lines\n"
	};

	static const char *decode_byte22_DDR2[] = {
		"  TBD (bit 7)\n",
		"  TBD (bit 6)\n",
		"  TBD (bit 5)\n",
		"  TBD (bit 4)\n",
		"  TBD (bit 3)\n",
		"  Supports partial array self refresh\n",
		"  Supports 50 ohm ODT\n",
		"  Supports weak driver\n"
	};

	static const char *decode_row_density_DDR2[] = {
		"512 MiB", "256 MiB", "128 MiB", "16 GiB",
		"8 GiB", "4 GiB", "2 GiB", "1 GiB"
	};

	static const char *decode_row_density_default[] = {
		"512 MiB", "256 MiB", "128 MiB", "64 MiB",
		"32 MiB", "16 MiB", "8 MiB", "4 MiB"
	};

	if (argc < 2)
		return CMD_RET_USAGE;

	/*
	 * Chip is always specified.
	 */
	chip = simple_strtoul (argv[1], NULL, 16);

	if (i2c_read (chip, 0, 1, data, sizeof (data)) != 0) {
		puts ("No SDRAM Serial Presence Detect found.\n");
		return 1;
	}

	cksum = 0;
	for (j = 0; j < 63; j++) {
		cksum += data[j];
	}
	if (cksum != data[63]) {
		printf ("WARNING: Configuration data checksum failure:\n"
			"  is 0x%02x, calculated 0x%02x\n", data[63], cksum);
	}
	printf ("SPD data revision            %d.%d\n",
		(data[62] >> 4) & 0x0F, data[62] & 0x0F);
	printf ("Bytes used                   0x%02X\n", data[0]);
	printf ("Serial memory size           0x%02X\n", 1 << data[1]);

	puts ("Memory type                  ");
	switch (data[2]) {
	case 2:
		type = EDO;
		puts ("EDO\n");
		break;
	case 4:
		type = SDRAM;
		puts ("SDRAM\n");
		break;
	case 8:
		type = DDR2;
		puts ("DDR2\n");
		break;
	default:
		type = unknown;
		puts ("unknown\n");
		break;
	}

	puts ("Row address bits             ");
	if ((data[3] & 0x00F0) == 0)
		printf ("%d\n", data[3] & 0x0F);
	else
		printf ("%d/%d\n", data[3] & 0x0F, (data[3] >> 4) & 0x0F);

	puts ("Column address bits          ");
	if ((data[4] & 0x00F0) == 0)
		printf ("%d\n", data[4] & 0x0F);
	else
		printf ("%d/%d\n", data[4] & 0x0F, (data[4] >> 4) & 0x0F);

	switch (type) {
	case DDR2:
		printf ("Number of ranks              %d\n",
			(data[5] & 0x07) + 1);
		break;
	default:
		printf ("Module rows                  %d\n", data[5]);
		break;
	}

	switch (type) {
	case DDR2:
		printf ("Module data width            %d bits\n", data[6]);
		break;
	default:
		printf ("Module data width            %d bits\n",
			(data[7] << 8) | data[6]);
		break;
	}

	puts ("Interface signal levels      ");
	switch(data[8]) {
		case 0:  puts ("TTL 5.0 V\n");	break;
		case 1:  puts ("LVTTL\n");	break;
		case 2:  puts ("HSTL 1.5 V\n");	break;
		case 3:  puts ("SSTL 3.3 V\n");	break;
		case 4:  puts ("SSTL 2.5 V\n");	break;
		case 5:  puts ("SSTL 1.8 V\n");	break;
		default: puts ("unknown\n");	break;
	}

	switch (type) {
	case DDR2:
		printf ("SDRAM cycle time             ");
		print_ddr2_tcyc (data[9]);
		break;
	default:
		printf ("SDRAM cycle time             %d.%d ns\n",