spi25.c

/*
 * This file is part of the flashrom project.
 *
 * Copyright (C) 2007, 2008, 2009, 2010 Carl-Daniel Hailfinger
 * Copyright (C) 2008 coresystems GmbH
 *
 * 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; version 2 of the License.
 *
 * 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.
 */

/*
 * Contains the common SPI chip driver functions
 */

#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include "flash.h"
#include "flashchips.h"
#include "chipdrivers.h"
#include "chipdrivers/spi.h"
#include "programmer.h"
#include "spi_command.h"
#include "spi.h"

static int spi_rdid(const struct spi_master *spi, unsigned char *readarr, int bytes)
{
	static const unsigned char cmd[JEDEC_RDID_OUTSIZE] = { JEDEC_RDID };
	int ret;
	int i;

	ret = spi->command(spi, sizeof(cmd), bytes, cmd, readarr);
	if (ret)
		return ret;
	msg_cspew("RDID returned");
	for (i = 0; i < bytes; i++)
		msg_cspew(" 0x%02x", readarr[i]);
	msg_cspew(". ");
	return 0;
}

static int spi_rems(const struct spi_master *spi, unsigned char *readarr)
{
	static const unsigned char cmd[JEDEC_REMS_OUTSIZE] = { JEDEC_REMS, };
	int ret;

	ret = spi->command(spi, sizeof(cmd), JEDEC_REMS_INSIZE, cmd, readarr);
	if (ret)
		return ret;
	msg_cspew("REMS returned 0x%02x 0x%02x. ", readarr[0], readarr[1]);
	return 0;
}

static int spi_res(const struct spi_master *spi, unsigned char *readarr, int bytes)
{
	static const unsigned char cmd[JEDEC_RES_OUTSIZE] = { JEDEC_RES, };
	int ret;
	int i;

	ret = spi->command(spi, sizeof(cmd), bytes, cmd, readarr);
	if (ret)
		return ret;
	msg_cspew("RES returned");
	for (i = 0; i < bytes; i++)
		msg_cspew(" 0x%02x", readarr[i]);
	msg_cspew(". ");
	return 0;
}

int spi_write_enable(struct flashctx *flash)
{
	static const unsigned char cmd[JEDEC_WREN_OUTSIZE] = { JEDEC_WREN };
	int result;

	/* Send WREN (Write Enable) */
	result = spi_send_command(flash, sizeof(cmd), 0, cmd, NULL);

	if (result)
		msg_cerr("%s failed\n", __func__);

	return result;
}

int spi_write_disable(struct flashctx *flash)
{
	static const unsigned char cmd[JEDEC_WRDI_OUTSIZE] = { JEDEC_WRDI };

	/* Send WRDI (Write Disable) */
	return spi_send_command(flash, sizeof(cmd), 0, cmd, NULL);
}

struct found_id *probe_spi_rdid(const struct bus_probe *probe, const struct master_common *mst)
{
	const struct spi_master *const spi = (const struct spi_master *)mst;
	unsigned char readarr[4];
	size_t bytes;
	int ret;

	for (bytes = 4; bytes >= 3; --bytes) {
		ret = spi_rdid(spi, readarr, bytes);
		if (ret == SPI_INVALID_LENGTH)
			msg_cinfo("%zu byte RDID not supported on this SPI controller\n", bytes);
		if (!ret)
			break;
	}
	if (ret || flashprog_no_data(readarr, bytes))
		return NULL;

	if (!oddparity(readarr[0]))
		msg_cdbg("RDID byte 0 parity violation. ");

	struct found_id *const found = calloc(1, sizeof(*found));
	if (!found) {
		msg_cerr("Out of memory!\n");
		return NULL;
	}

	struct id_info *const id = &found->info.id;
	id->type = ID_SPI_RDID;

	/* Check if this is a continuation vendor ID.
	 * FIXME: Handle continuation device IDs.
	 */
	if (readarr[0] == 0x7f) {
		if (!oddparity(readarr[1]))
			msg_cdbg("RDID byte 1 parity violation. ");
		id->manufacture = (readarr[0] << 8) | readarr[1];
		id->model = readarr[2];
		if (bytes > 3) {
			id->model <<= 8;
			id->model |= readarr[3];
		}
	} else {
		id->manufacture = readarr[0];
		id->model = (readarr[1] << 8) | readarr[2];
	}

	msg_cdbg("%s: id1 0x%02x, id2 0x%02x\n", __func__, id->id1, id->id2);

	return found;
}

struct found_id *probe_spi_rems(const struct bus_probe *probe, const struct master_common *mst)
{
	const struct spi_master *const spi = (const struct spi_master *)mst;
	unsigned char readarr[JEDEC_REMS_INSIZE];

	if (spi_rems(spi, readarr) || flashprog_no_data(readarr, sizeof(readarr))) {
		return NULL;
	}

	struct found_id *const found = calloc(1, sizeof(*found));
	if (!found) {
		msg_cerr("Out of memory!\n");
		return NULL;
	}

	struct id_info *const id = &found->info.id;

	id->manufacture	= readarr[0];
	id->model	= readarr[1];
	id->type	= ID_SPI_REMS;

	msg_cdbg("%s: id1 0x%02x, id2 0x%02x\n", __func__, id->id1, id->id2);

	return found;
}

struct found_id *probe_spi_res(const struct bus_probe *probe, const struct master_common *mst)
{
	const struct spi_master *const spi = (const struct spi_master *)mst;
	const unsigned int res_len = probe->type == ID_SPI_RES3 ? 3 :
				    (probe->type == ID_SPI_RES2 ? 2 : 1);
	unsigned char readarr[3];

	if (res_len == 1) {
		/* We only want one-byte RES if RDID and REMS are unusable. */

		if (!spi_rdid(spi, readarr, 3) && !flashprog_no_data(readarr, 3)) {
			msg_cdbg("Ignoring RES in favour of RDID.\n");
			return NULL;
		}

		if (!spi_rems(spi, readarr) && !flashprog_no_data(readarr, JEDEC_REMS_INSIZE)) {
			msg_cdbg("Ignoring RES in favour of REMS.\n");
			return NULL;
		}
	}

	if (spi_res(spi, readarr, res_len) || flashprog_no_data(readarr, res_len)) {
		return NULL;
	}

	struct found_id *const found = calloc(1, sizeof(*found));
	if (!found) {
		msg_cerr("Out of memory!\n");
		return NULL;
	}

	struct id_info *const id = &found->info.id;

	switch (res_len) {
	case 1:
		id->manufacture	= 0;
		id->model	= readarr[0];
		msg_cdbg("%s: id 0x%02x\n", __func__, id->model);
		break;
	case 2:
		id->manufacture	= readarr[0];
		id->model	= readarr[1];
		msg_cdbg("%s: id1 0x%02x, id2 0x%02x\n", __func__, id->id1, id->id2);
		break;
	case 3:
		id->manufacture	= (readarr[0] << 8) | readarr[1];
		id->model	= readarr[2];
		msg_cdbg("%s: id1 0x%04x, id2 0x%02x\n", __func__, id->id1, id->id2);
		break;
	}
	id->type = probe->type;

	return found;
}

/* Only used for some Atmel chips. */
struct found_id *probe_spi_at25f(const struct bus_probe *probe, const struct master_common *mst)
{
	static const unsigned char cmd[AT25F_RDID_OUTSIZE] = { AT25F_RDID };
	const struct spi_master *const spi = (const struct spi_master *)mst;
	unsigned char readarr[AT25F_RDID_INSIZE];

	if (spi->command(spi, sizeof(cmd), sizeof(readarr), cmd, readarr))
		return NULL;
	if (flashprog_no_data(readarr, sizeof(readarr)))
		return NULL;

	struct found_id *const found = calloc(1, sizeof(*found));
	if (!found) {
		msg_cerr("Out of memory!\n");
		return NULL;
	}

	struct id_info *const id = &found->info.id;

	id->manufacture	= readarr[0];
	id->model	= readarr[1];
	id->type	= ID_SPI_AT25F;

	msg_cdbg("%s: id1 0x%02x, id2 0x%02x\n", __func__, id->id1, id->id2);

	return found;
}

static int spi_poll_wip(struct flashctx *const flash, const unsigned int poll_delay)
{
	/* FIXME: We don't time out. */
	while (true) {
		uint8_t status;
		int ret = spi_read_register(flash, STATUS1, &status);
		if (ret)
			return ret;
		if (!(status & SPI_SR_WIP))
			return 0;

		programmer_delay(poll_delay);
	}
}

/**
 * Execute WREN plus another one byte `op`, optionally poll WIP afterwards.
 *
 * @param flash       the flash chip's context
 * @param op          the operation to execute
 * @param poll_delay  interval in us for polling WIP, don't poll if zero
 * @return 0 on success, non-zero otherwise
 */
int spi_simple_write_cmd(struct flashctx *const flash, const uint8_t op, const unsigned int poll_delay)
{
	struct spi_command cmds[] = {
	{
		.io_mode = spi_current_io_mode(flash),
		.readarr = 0,
		.opcode_len = 1,
		.writearr = (const unsigned char[]){ JEDEC_WREN },
	}, {
		.io_mode = spi_current_io_mode(flash),
		.readarr = 0,
		.opcode_len = 1,
		.writearr = (const unsigned char[]){ op },
	},
		NULL_SPI_CMD,
	};

	const int result = spi_send_multicommand(flash, cmds);
	if (result)
		msg_cerr("%s failed during command execution\n", __func__);

	const int status = poll_delay ? spi_poll_wip(flash, poll_delay) : 0;

	return result ? result : status;
}

static int spi_write_extended_address_register(struct flashctx *const flash, const uint8_t regdata)
{
	uint8_t op;
	if (flash->chip->feature_bits & FEATURE_4BA_EAR_C5C8) {
		op = JEDEC_WRITE_EXT_ADDR_REG;
	} else if (flash->chip->feature_bits & FEATURE_4BA_EAR_1716) {
		op = ALT_WRITE_EXT_ADDR_REG_17;
	} else {
		msg_cerr("Flash misses feature flag for extended-address register.\n");
		return -1;
	}

	struct spi_command cmds[] = {
	{
		.io_mode = spi_current_io_mode(flash),
		.readarr = 0,
		.opcode_len = 1,
		.writearr = (const unsigned char[]){ JEDEC_WREN },
	}, {
		.io_mode = spi_current_io_mode(flash),
		.readarr = 0,
		.opcode_len = 1,
		.write_len = 1,
		.writearr = (const unsigned char[]){ op, regdata },
	},
		NULL_SPI_CMD,
	};

	const int result = spi_send_multicommand(flash, cmds);
	if (result)
		msg_cerr("%s failed during command execution\n", __func__);
	return result;
}

int spi_set_extended_address(struct flashctx *const flash, const uint8_t addr_high)
{
	if (flash->address_high_byte != addr_high &&
	    spi_write_extended_address_register(flash, addr_high))
		return -1;
	flash->address_high_byte = addr_high;
	return 0;
}

static size_t spi_address_length(struct flashctx *const flash, const bool native_4ba)
{
	if (flash->chip->spi_cmd_set == SPI25_EEPROM) {
		if (flashprog_flash_getsize(flash) > 64*KiB)
			return 3;
		if (flashprog_flash_getsize(flash) > 256)
			return 2;
		return 1;
	}

	if (native_4ba || flash->in_4ba_mode)
		return 4;

	return 3;
}

static int spi_prepare_address(struct flashctx *const flash, uint8_t cmd_buf[],
			       const bool native_4ba, const unsigned int rel_addr)
{
	const size_t len = spi_address_length(flash, native_4ba);
	unsigned int addr = rel_addr;

	if (spi_master_top_aligned(flash))
		addr = rel_addr - flashprog_flash_getsize(flash); /* intentional integer underflow */

	switch (len) {
	case 4:
		if (!spi_master_4ba(flash)) {
			msg_cwarn("4-byte address requested but master can't handle 4-byte addresses.\n");
			return -1;
		}
		cmd_buf[1] = (addr >> 24) & 0xff;
		cmd_buf[2] = (addr >> 16) & 0xff;
		cmd_buf[3] = (addr >>  8) & 0xff;
		cmd_buf[4] = (addr >>  0) & 0xff;
		return len;
	case 3:
		if (flash->chip->feature_bits & FEATURE_4BA_EAR_ANY) {
			if (spi_set_extended_address(flash, rel_addr >> 24))
				return -1;
		} else if (rel_addr >> 24) {
			msg_cerr("Can't handle 4-byte address for opcode '0x%02x'\n"
				 "with this chip/programmer combination.\n", cmd_buf[0]);
			return -1;
		}
		cmd_buf[1] = (addr >> 16) & 0xff;
		cmd_buf[2] = (addr >>  8) & 0xff;
		cmd_buf[3] = (addr >>  0) & 0xff;
		return len;
	case 2:
		cmd_buf[1] = (addr >> 8) & 0xff;
		cmd_buf[2] = (addr >> 0) & 0xff;
		return len;
	default:
		cmd_buf[1] = addr & 0xff;
		return len;
	}
}

/**
 * Execute WREN plus another `op` that takes an address and
 * optional data, poll WIP afterwards.
 *
 * @param flash       the flash chip's context
 * @param op          the operation to execute
 * @param native_4ba  whether `op` always takes a 4-byte address
 * @param addr        the address parameter to `op`
 * @param out_bytes   bytes to send after the address,
 *                    may be NULL if and only if `out_bytes` is 0
 * @param out_bytes   number of bytes to send, 256 at most, may be zero
 * @param poll_delay  interval in us for polling WIP
 * @return 0 on success, non-zero otherwise
 */
static int spi_write_cmd(struct flashctx *const flash, const uint8_t op,
			 const bool native_4ba, const unsigned int addr,
			 const uint8_t *const out_bytes, const size_t out_len,
			 const unsigned int poll_delay)
{
	uint8_t cmd[1 + JEDEC_MAX_ADDR_LEN + 256];
	struct spi_command cmds[] = {
	{
		.io_mode = spi_current_io_mode(flash),
		.readarr = 0,
		.opcode_len = 1,
		.writearr = (const unsigned char[]){ JEDEC_WREN },
	}, {
		.io_mode = spi_current_io_mode(flash),
		.readarr = 0,
		.writearr = cmd,
	},
		NULL_SPI_CMD,
	};

	cmd[0] = op;
	const int addr_len = spi_prepare_address(flash, cmd, native_4ba, addr);
	if (addr_len < 0)
		return 1;

	if (1 + addr_len + out_len > sizeof(cmd)) {
		msg_cerr("%s called for too long a write\n", __func__);
		return 1;
	}
	if (!out_bytes && out_len > 0)
		return 1;

	memcpy(cmd + 1 + addr_len, out_bytes, out_len);
	cmds[1].opcode_len  = 1;
	cmds[1].address_len = addr_len;
	cmds[1].write_len   = out_len;

	const int result = spi_send_multicommand(flash, cmds);
	if (result)
		msg_cerr("%s failed during command execution at address 0x%x\n", __func__, addr);

	const int status = spi_poll_wip(flash, poll_delay);

	return result ? result : status;
}

static int spi_chip_erase_60(struct flashctx *flash)
{
	/* This usually takes 1-85s, so wait in 1s steps. */
	return spi_simple_write_cmd(flash, 0x60, 1000 * 1000);
}

static int spi_chip_erase_62(struct flashctx *flash)
{
	/* This usually takes 2-5s, so wait in 100ms steps. */
	return spi_simple_write_cmd(flash, 0x62, 100 * 1000);
}

static int spi_chip_erase_c7(struct flashctx *flash)
{
	/* This usually takes 1-85s, so wait in 1s steps. */
	return spi_simple_write_cmd(flash, 0xc7, 1000 * 1000);
}

int spi_block_erase_52(struct flashctx *flash, unsigned int addr,
		       unsigned int blocklen)
{
	/* This usually takes 100-4000ms, so wait in 100ms steps. */
	return spi_write_cmd(flash, 0x52, false, addr, NULL, 0, 100 * 1000);
}

/* Block size is usually
 * 32M (one die) for Micron
 */
int spi_block_erase_c4(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 240-480s, so wait in 500ms steps. */
	return spi_write_cmd(flash, 0xc4, false, addr, NULL, 0, 500 * 1000);
}

/* Block size is usually
 * 64k for Macronix
 * 32k for SST
 * 4-32k non-uniform for EON
 */
int spi_block_erase_d8(struct flashctx *flash, unsigned int addr,
		       unsigned int blocklen)
{
	/* This usually takes 100-4000ms, so wait in 100ms steps. */
	return spi_write_cmd(flash, 0xd8, false, addr, NULL, 0, 100 * 1000);
}

/* Block size is usually
 * 4k for PMC
 */
int spi_block_erase_d7(struct flashctx *flash, unsigned int addr,
		       unsigned int blocklen)
{
	/* This usually takes 100-4000ms, so wait in 100ms steps. */
	return spi_write_cmd(flash, 0xd7, false, addr, NULL, 0, 100 * 1000);
}

/* Page erase (usually 256B blocks) */
int spi_block_erase_db(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This takes up to 20ms usually (on worn out devices
	   up to the 0.5s range), so wait in 1ms steps. */
	return spi_write_cmd(flash, 0xdb, false, addr, NULL, 0, 1 * 1000);
}

/* Sector size is usually 4k, though Macronix eliteflash has 64k */
int spi_block_erase_20(struct flashctx *flash, unsigned int addr,
		       unsigned int blocklen)
{
	/* This usually takes 15-800ms, so wait in 10ms steps. */
	return spi_write_cmd(flash, 0x20, false, addr, NULL, 0, 10 * 1000);
}

int spi_block_erase_50(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 10ms, so wait in 1ms steps. */
	return spi_write_cmd(flash, 0x50, false, addr, NULL, 0, 1 * 1000);
}

int spi_block_erase_81(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 8ms, so wait in 1ms steps. */
	return spi_write_cmd(flash, 0x81, false, addr, NULL, 0, 1 * 1000);
}

int spi_block_erase_60(struct flashctx *flash, unsigned int addr,
		       unsigned int blocklen)
{
	if ((addr != 0) || (blocklen != flash->chip->total_size * 1024)) {
		msg_cerr("%s called with incorrect arguments\n",
			__func__);
		return -1;
	}
	return spi_chip_erase_60(flash);
}

int spi_block_erase_62(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	if ((addr != 0) || (blocklen != flash->chip->total_size * 1024)) {
		msg_cerr("%s called with incorrect arguments\n",
			__func__);
		return -1;
	}
	return spi_chip_erase_62(flash);
}

int spi_block_erase_c7(struct flashctx *flash, unsigned int addr,
		       unsigned int blocklen)
{
	if ((addr != 0) || (blocklen != flash->chip->total_size * 1024)) {
		msg_cerr("%s called with incorrect arguments\n",
			__func__);
		return -1;
	}
	return spi_chip_erase_c7(flash);
}

/* Erase 4 KB of flash with 4-bytes address from ANY mode (3-bytes or 4-bytes) */
int spi_block_erase_21(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 15-800ms, so wait in 10ms steps. */
	return spi_write_cmd(flash, 0x21, true, addr, NULL, 0, 10 * 1000);
}

/* Erase 32 KB of flash with 4-bytes address from ANY mode (3-bytes or 4-bytes) */
int spi_block_erase_53(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 100-4000ms, so wait in 100ms steps. */
	return spi_write_cmd(flash, 0x53, true, addr, NULL, 0, 100 * 1000);
}

/* Erase 32 KB of flash with 4-bytes address from ANY mode (3-bytes or 4-bytes) */
int spi_block_erase_5c(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 100-4000ms, so wait in 100ms steps. */
	return spi_write_cmd(flash, 0x5c, true, addr, NULL, 0, 100 * 1000);
}

/* Erase 64 KB of flash with 4-bytes address from ANY mode (3-bytes or 4-bytes) */
int spi_block_erase_dc(struct flashctx *flash, unsigned int addr, unsigned int blocklen)
{
	/* This usually takes 100-4000ms, so wait in 100ms steps. */
	return spi_write_cmd(flash, 0xdc, true, addr, NULL, 0, 100 * 1000);
}

static const struct {
	erasefunc_t *func;
	uint8_t opcode;
} spi25_function_opcode_list[] = {
	{&spi_block_erase_20, 0x20},
	{&spi_block_erase_21, 0x21},
	{&spi_block_erase_50, 0x50},
	{&spi_block_erase_52, 0x52},
	{&spi_block_erase_53, 0x53},
	{&spi_block_erase_5c, 0x5c},
	{&spi_block_erase_60, 0x60},
	{&spi_block_erase_62, 0x62},
	{&spi_block_erase_81, 0x81},
	{&spi_block_erase_c4, 0xc4},
	{&spi_block_erase_c7, 0xc7},
	{&spi_block_erase_d7, 0xd7},
	{&spi_block_erase_d8, 0xd8},
	{&spi_block_erase_db, 0xdb},
	{&spi_block_erase_dc, 0xdc},
};

erasefunc_t *spi25_get_erasefn_from_opcode(uint8_t opcode)
{
	size_t i;
	for (i = 0; i < ARRAY_SIZE(spi25_function_opcode_list); i++) {
		if (spi25_function_opcode_list[i].opcode == opcode)
			return spi25_function_opcode_list[i].func;
	}
	msg_cinfo("%s: unknown erase opcode (0x%02x). Please report "
			  "this at flashprog@flashprog.org\n", __func__, opcode);
	return NULL;
}

static int spi_nbyte_program(struct flashctx *flash, unsigned int addr, const uint8_t *bytes, unsigned int len)
{
	const bool native_4ba = flash->chip->feature_bits & FEATURE_4BA_WRITE && spi_master_4ba(flash);
	const uint8_t op = native_4ba ? JEDEC_BYTE_PROGRAM_4BA : JEDEC_BYTE_PROGRAM;
	return spi_write_cmd(flash, op, native_4ba, addr, bytes, len, 10);
}

const struct spi_read_op *get_spi_read_op(const struct flashctx *flash)
{
	static const struct spi_read_op sio_read = { SINGLE_IO_1_1_1, false, JEDEC_READ, 0x00, 0 };
	static const struct spi_read_op sio_read_4ba = { SINGLE_IO_1_1_1, true, JEDEC_READ_4BA, 0x00, 0 };

	if (flash->spi_fast_read)
		return flash->spi_fast_read;

	if (flash->chip->feature_bits & FEATURE_4BA_READ && spi_master_4ba(flash))
		return &sio_read_4ba;

	return &sio_read;
}

int spi_nbyte_read(struct flashctx *flash, uint8_t *dst, unsigned int address, unsigned int len)
{
	const struct spi_read_op *const read_op = get_spi_read_op(flash);
	const size_t mode_len = read_op->mode_byte ? 1 : 0;
	uint8_t cmd_buf[1 + JEDEC_MAX_ADDR_LEN + 1] = { read_op->opcode, };

	const int addr_len = spi_prepare_address(flash, cmd_buf, read_op->native_4ba, address);
	if (addr_len < 0)
		return 1;

	cmd_buf[addr_len + 1] = read_op->mode_byte;

	struct spi_command cmd[] = {
	{
		.io_mode	= read_op->io_mode,
		.opcode_len	= 1,
		.address_len	= addr_len,
		.write_len	= mode_len,
		.high_z_len	= read_op->dummy_len - mode_len,
		.read_len	= len,
		.writearr	= cmd_buf,
		.readarr	= dst,
	},
		NULL_SPI_CMD
	};

	return spi_send_multicommand(flash, cmd);
}

/*
 * Write a part of the flash chip.
 * FIXME: Use the chunk code from Michael Karcher instead.
 * Each page is written separately in chunks with a maximum size of chunksize.
 */
int spi_write_chunked(struct flashctx *flash, const uint8_t *buf, unsigned int start,
		      unsigned int len, unsigned int chunksize)
{
	unsigned int i, j, starthere, lenhere, towrite;
	/* FIXME: page_size is the wrong variable. We need max_writechunk_size
	 * in struct flashctx to do this properly. All chips using
	 * spi_chip_write_256 have page_size set to max_writechunk_size, so
	 * we're OK for now.
	 */
	unsigned int page_size = flash->chip->page_size;

	/* Warning: This loop has a very unusual condition and body.
	 * The loop needs to go through each page with at least one affected
	 * byte. The lowest page number is (start / page_size) since that
	 * division rounds down. The highest page number we want is the page
	 * where the last byte of the range lives. That last byte has the
	 * address (start + len - 1), thus the highest page number is
	 * (start + len - 1) / page_size. Since we want to include that last
	 * page as well, the loop condition uses <=.
	 */
	for (i = start / page_size; i <= (start + len - 1) / page_size; i++) {
		/* Byte position of the first byte in the range in this page. */
		/* starthere is an offset to the base address of the chip. */
		starthere = max(start, i * page_size);
		/* Length of bytes in the range in this page. */
		lenhere = min(start + len, (i + 1) * page_size) - starthere;
		for (j = 0; j < lenhere; j += chunksize) {
			int rc;

			towrite = min(chunksize, lenhere - j);
			rc = spi_nbyte_program(flash, starthere + j, buf + starthere - start + j, towrite);
			if (rc)
				return rc;
			flashprog_progress_add(flash, towrite);
		}
	}

	return 0;
}

/*
 * Program chip using byte programming. (SLOW!)
 * This is for chips which can only handle one byte writes
 * and for chips where memory mapped programming is impossible
 * (e.g. due to size constraints in IT87* for over 512 kB)
 */
/* real chunksize is 1, logical chunksize is 1 */
int spi_chip_write_1(struct flashctx *flash, const uint8_t *buf, unsigned int start, unsigned int len)
{
	unsigned int i;

	for (i = start; i < start + len; i++) {
		if (spi_nbyte_program(flash, i, buf + i - start, 1))
			return 1;
		flashprog_progress_add(flash, 1);
	}
	return 0;
}

int default_spi_write_aai(struct flashctx *flash, const uint8_t *buf, unsigned int start, unsigned int len)
{
	uint32_t pos = start;
	int result;
	unsigned char cmd[JEDEC_AAI_WORD_PROGRAM_CONT_OUTSIZE] = {
		JEDEC_AAI_WORD_PROGRAM,
	};

	/* The even start address and even length requirements can be either
	 * honored outside this function, or we can call spi_byte_program
	 * for the first and/or last byte and use AAI for the rest.
	 * FIXME: Move this to generic code.
	 */
	/* The data sheet requires a start address with the low bit cleared. */
	if (start % 2) {
		msg_cerr("%s: start address not even!\n"
			 "Please report a bug at flashprog@flashprog.org\n",
			 __func__);
		if (spi_chip_write_1(flash, buf, start, start % 2))
			return SPI_GENERIC_ERROR;
		pos += start % 2;
		/* Do not return an error for now. */
		//return SPI_GENERIC_ERROR;
	}
	/* The data sheet requires total AAI write length to be even. */
	if (len % 2) {
		msg_cerr("%s: total write length not even!\n"
			 "Please report a bug at flashprog@flashprog.org\n",
			 __func__);
		/* Do not return an error for now. */
		//return SPI_GENERIC_ERROR;
	}

	result = spi_write_cmd(flash, JEDEC_AAI_WORD_PROGRAM, false, start, buf + pos - start, 2, 10);
	if (result)
		goto bailout;

	/* We already wrote 2 bytes in the multicommand step. */
	flashprog_progress_add(flash, 2);
	pos += 2;

	/* Are there at least two more bytes to write? */
	while (pos < start + len - 1) {
		cmd[1] = buf[pos++ - start];
		cmd[2] = buf[pos++ - start];
		result = spi_send_command(flash, JEDEC_AAI_WORD_PROGRAM_CONT_OUTSIZE, 0, cmd, NULL);
		if (result != 0) {
			msg_cerr("%s failed during followup AAI command execution: %d\n", __func__, result);
			goto bailout;
		}
		if (spi_poll_wip(flash, 10))
			goto bailout;
		flashprog_progress_add(flash, 2);
	}

	/* Use WRDI to exit AAI mode. This needs to be done before issuing any other non-AAI command. */
	result = spi_write_disable(flash);
	if (result != 0) {
		msg_cerr("%s failed to disable AAI mode.\n", __func__);
		return SPI_GENERIC_ERROR;
	}

	/* Write remaining byte (if any). */
	if (pos < start + len) {
		if (spi_chip_write_1(flash, buf + pos - start, pos, pos % 2))
			return SPI_GENERIC_ERROR;
	}

	return 0;

bailout:
	result = spi_write_disable(flash);
	if (result != 0)
		msg_cerr("%s failed to disable AAI mode.\n", __func__);
	return SPI_GENERIC_ERROR;
}