drivers/infiniband/hw/qib/qib_twsi.c - hafnium/third_party/linux - Git at Google

 /*
  * Copyright (c) 2012 Intel Corporation. All rights reserved.
  * Copyright (c) 2006 - 2012 QLogic Corporation. All rights reserved.
  * Copyright (c) 2003, 2004, 2005, 2006 PathScale, Inc. All rights reserved.
  *
  * This software is available to you under a choice of one of two
  * licenses.  You may choose to be licensed under the terms of the GNU
  * General Public License (GPL) Version 2, available from the file
  * COPYING in the main directory of this source tree, or the
  * OpenIB.org BSD license below:
  *
  *     Redistribution and use in source and binary forms, with or
  *     without modification, are permitted provided that the following
  *     conditions are met:
  *
  *      - Redistributions of source code must retain the above
  *        copyright notice, this list of conditions and the following
  *        disclaimer.
  *
  *      - Redistributions in binary form must reproduce the above
  *        copyright notice, this list of conditions and the following
  *        disclaimer in the documentation and/or other materials
  *        provided with the distribution.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */

 #include <linux/delay.h>
 #include <linux/pci.h>
 #include <linux/vmalloc.h>

 #include "qib.h"

 /*
  * QLogic_IB "Two Wire Serial Interface" driver.
  * Originally written for a not-quite-i2c serial eeprom, which is
  * still used on some supported boards. Later boards have added a
  * variety of other uses, most board-specific, so the bit-boffing
  * part has been split off to this file, while the other parts
  * have been moved to chip-specific files.
  *
  * We have also dropped all pretense of fully generic (e.g. pretend
  * we don't know whether '1' is the higher voltage) interface, as
  * the restrictions of the generic i2c interface (e.g. no access from
  * driver itself) make it unsuitable for this use.
  */

 #define READ_CMD 1
 #define WRITE_CMD 0

 /**
  * i2c_wait_for_writes - wait for a write
  * @dd: the qlogic_ib device
  *
  * We use this instead of udelay directly, so we can make sure
  * that previous register writes have been flushed all the way
  * to the chip.  Since we are delaying anyway, the cost doesn't
  * hurt, and makes the bit twiddling more regular
  */
 static void i2c_wait_for_writes(struct qib_devdata *dd)
 {
 	/*
 	 * implicit read of EXTStatus is as good as explicit
 	 * read of scratch, if all we want to do is flush
 	 * writes.
 	 */
 	dd->f_gpio_mod(dd, 0, 0, 0);
 	rmb(); /* inlined, so prevent compiler reordering */
 }

 /*
  * QSFP modules are allowed to hold SCL low for 500uSec. Allow twice that
  * for "almost compliant" modules
  */
 #define SCL_WAIT_USEC 1000

 /* BUF_WAIT is time bus must be free between STOP or ACK and to next START.
  * Should be 20, but some chips need more.
  */
 #define TWSI_BUF_WAIT_USEC 60

 static void scl_out(struct qib_devdata *dd, u8 bit)
 {
 	u32 mask;

 	udelay(1);

 	mask = 1UL << dd->gpio_scl_num;

 	/* SCL is meant to be bare-drain, so never set "OUT", just DIR */
 	dd->f_gpio_mod(dd, 0, bit ? 0 : mask, mask);

 	/*
 	 * Allow for slow slaves by simple
 	 * delay for falling edge, sampling on rise.
 	 */
 	if (!bit)
 		udelay(2);
 	else {
 		int rise_usec;

 		for (rise_usec = SCL_WAIT_USEC; rise_usec > 0; rise_usec -= 2) {
 			if (mask & dd->f_gpio_mod(dd, 0, 0, 0))
 				break;
 			udelay(2);
 		}
 		if (rise_usec <= 0)
 			qib_dev_err(dd, "SCL interface stuck low > %d uSec\n",
 				    SCL_WAIT_USEC);
 	}
 	i2c_wait_for_writes(dd);
 }

 static void sda_out(struct qib_devdata *dd, u8 bit)
 {
 	u32 mask;

 	mask = 1UL << dd->gpio_sda_num;

 	/* SDA is meant to be bare-drain, so never set "OUT", just DIR */
 	dd->f_gpio_mod(dd, 0, bit ? 0 : mask, mask);

 	i2c_wait_for_writes(dd);
 	udelay(2);
 }

 static u8 sda_in(struct qib_devdata *dd, int wait)
 {
 	int bnum;
 	u32 read_val, mask;

 	bnum = dd->gpio_sda_num;
 	mask = (1UL << bnum);
 	/* SDA is meant to be bare-drain, so never set "OUT", just DIR */
 	dd->f_gpio_mod(dd, 0, 0, mask);
 	read_val = dd->f_gpio_mod(dd, 0, 0, 0);
 	if (wait)
 		i2c_wait_for_writes(dd);
 	return (read_val & mask) >> bnum;
 }

 /**
  * i2c_ackrcv - see if ack following write is true
  * @dd: the qlogic_ib device
  */
 static int i2c_ackrcv(struct qib_devdata *dd)
 {
 	u8 ack_received;

 	/* AT ENTRY SCL = LOW */
 	/* change direction, ignore data */
 	ack_received = sda_in(dd, 1);
 	scl_out(dd, 1);
 	ack_received = sda_in(dd, 1) == 0;
 	scl_out(dd, 0);
 	return ack_received;
 }

 static void stop_cmd(struct qib_devdata *dd);

 /**
  * rd_byte - read a byte, sending STOP on last, else ACK
  * @dd: the qlogic_ib device
  *
  * Returns byte shifted out of device
  */
 static int rd_byte(struct qib_devdata *dd, int last)
 {
 	int bit_cntr, data;

 	data = 0;

 	for (bit_cntr = 7; bit_cntr >= 0; --bit_cntr) {
 		data <<= 1;
 		scl_out(dd, 1);
 		data |= sda_in(dd, 0);
 		scl_out(dd, 0);
 	}
 	if (last) {
 		scl_out(dd, 1);
 		stop_cmd(dd);
 	} else {
 		sda_out(dd, 0);
 		scl_out(dd, 1);
 		scl_out(dd, 0);
 		sda_out(dd, 1);
 	}
 	return data;
 }

 /**
  * wr_byte - write a byte, one bit at a time
  * @dd: the qlogic_ib device
  * @data: the byte to write
  *
  * Returns 0 if we got the following ack, otherwise 1
  */
 static int wr_byte(struct qib_devdata *dd, u8 data)
 {
 	int bit_cntr;
 	u8 bit;

 	for (bit_cntr = 7; bit_cntr >= 0; bit_cntr--) {
 		bit = (data >> bit_cntr) & 1;
 		sda_out(dd, bit);
 		scl_out(dd, 1);
 		scl_out(dd, 0);
 	}
 	return (!i2c_ackrcv(dd)) ? 1 : 0;
 }

 /*
  * issue TWSI start sequence:
  * (both clock/data high, clock high, data low while clock is high)
  */
 static void start_seq(struct qib_devdata *dd)
 {
 	sda_out(dd, 1);
 	scl_out(dd, 1);
 	sda_out(dd, 0);
 	udelay(1);
 	scl_out(dd, 0);
 }

 /**
  * stop_seq - transmit the stop sequence
  * @dd: the qlogic_ib device
  *
  * (both clock/data low, clock high, data high while clock is high)
  */
 static void stop_seq(struct qib_devdata *dd)
 {
 	scl_out(dd, 0);
 	sda_out(dd, 0);
 	scl_out(dd, 1);
 	sda_out(dd, 1);
 }

 /**
  * stop_cmd - transmit the stop condition
  * @dd: the qlogic_ib device
  *
  * (both clock/data low, clock high, data high while clock is high)
  */
 static void stop_cmd(struct qib_devdata *dd)
 {
 	stop_seq(dd);
 	udelay(TWSI_BUF_WAIT_USEC);
 }

 /**
  * qib_twsi_reset - reset I2C communication
  * @dd: the qlogic_ib device
  */

 int qib_twsi_reset(struct qib_devdata *dd)
 {
 	int clock_cycles_left = 9;
 	int was_high = 0;
 	u32 pins, mask;

 	/* Both SCL and SDA should be high. If not, there
 	 * is something wrong.
 	 */
 	mask = (1UL << dd->gpio_scl_num) | (1UL << dd->gpio_sda_num);

 	/*
 	 * Force pins to desired innocuous state.
 	 * This is the default power-on state with out=0 and dir=0,
 	 * So tri-stated and should be floating high (barring HW problems)
 	 */
 	dd->f_gpio_mod(dd, 0, 0, mask);

 	/*
 	 * Clock nine times to get all listeners into a sane state.
 	 * If SDA does not go high at any point, we are wedged.
 	 * One vendor recommends then issuing START followed by STOP.
 	 * we cannot use our "normal" functions to do that, because
 	 * if SCL drops between them, another vendor's part will
 	 * wedge, dropping SDA and keeping it low forever, at the end of
 	 * the next transaction (even if it was not the device addressed).
 	 * So our START and STOP take place with SCL held high.
 	 */
 	while (clock_cycles_left--) {
 		scl_out(dd, 0);
 		scl_out(dd, 1);
 		/* Note if SDA is high, but keep clocking to sync slave */
 		was_high |= sda_in(dd, 0);
 	}

 	if (was_high) {
 		/*
 		 * We saw a high, which we hope means the slave is sync'd.
 		 * Issue START, STOP, pause for T_BUF.
 		 */

 		pins = dd->f_gpio_mod(dd, 0, 0, 0);
 		if ((pins & mask) != mask)
 			qib_dev_err(dd, "GPIO pins not at rest: %d\n",
 				    pins & mask);
 		/* Drop SDA to issue START */
 		udelay(1); /* Guarantee .6 uSec setup */
 		sda_out(dd, 0);
 		udelay(1); /* Guarantee .6 uSec hold */
 		/* At this point, SCL is high, SDA low. Raise SDA for STOP */
 		sda_out(dd, 1);
 		udelay(TWSI_BUF_WAIT_USEC);
 	}

 	return !was_high;
 }

 #define QIB_TWSI_START 0x100
 #define QIB_TWSI_STOP 0x200

 /* Write byte to TWSI, optionally prefixed with START or suffixed with
  * STOP.
  * returns 0 if OK (ACK received), else != 0
  */
 static int qib_twsi_wr(struct qib_devdata *dd, int data, int flags)
 {
 	int ret = 1;

 	if (flags & QIB_TWSI_START)
 		start_seq(dd);

 	ret = wr_byte(dd, data); /* Leaves SCL low (from i2c_ackrcv()) */

 	if (flags & QIB_TWSI_STOP)
 		stop_cmd(dd);
 	return ret;
 }

 /* Added functionality for IBA7220-based cards */
 #define QIB_TEMP_DEV 0x98

 /*
  * qib_twsi_blk_rd
  * Formerly called qib_eeprom_internal_read, and only used for eeprom,
  * but now the general interface for data transfer from twsi devices.
  * One vestige of its former role is that it recognizes a device
  * QIB_TWSI_NO_DEV and does the correct operation for the legacy part,
  * which responded to all TWSI device codes, interpreting them as
  * address within device. On all other devices found on board handled by
  * this driver, the device is followed by a one-byte "address" which selects
  * the "register" or "offset" within the device from which data should
  * be read.
  */
 int qib_twsi_blk_rd(struct qib_devdata *dd, int dev, int addr,
 		    void *buffer, int len)
 {
 	int ret;
 	u8 *bp = buffer;

 	ret = 1;

 	if (dev == QIB_TWSI_NO_DEV) {
 		/* legacy not-really-I2C */
 		addr = (addr << 1) | READ_CMD;
 		ret = qib_twsi_wr(dd, addr, QIB_TWSI_START);
 	} else {
 		/* Actual I2C */
 		ret = qib_twsi_wr(dd, dev | WRITE_CMD, QIB_TWSI_START);
 		if (ret) {
 			stop_cmd(dd);
 			ret = 1;
 			goto bail;
 		}
 		/*
 		 * SFF spec claims we do _not_ stop after the addr
 		 * but simply issue a start with the "read" dev-addr.
 		 * Since we are implicitely waiting for ACK here,
 		 * we need t_buf (nominally 20uSec) before that start,
 		 * and cannot rely on the delay built in to the STOP
 		 */
 		ret = qib_twsi_wr(dd, addr, 0);
 		udelay(TWSI_BUF_WAIT_USEC);

 		if (ret) {
 			qib_dev_err(dd,
 				"Failed to write interface read addr %02X\n",
 				addr);
 			ret = 1;
 			goto bail;
 		}
 		ret = qib_twsi_wr(dd, dev | READ_CMD, QIB_TWSI_START);
 	}
 	if (ret) {
 		stop_cmd(dd);
 		ret = 1;
 		goto bail;
 	}

 	/*
 	 * block devices keeps clocking data out as long as we ack,
 	 * automatically incrementing the address. Some have "pages"
 	 * whose boundaries will not be crossed, but the handling
 	 * of these is left to the caller, who is in a better
 	 * position to know.
 	 */
 	while (len-- > 0) {
 		/*
 		 * Get and store data, sending ACK if length remaining,
 		 * else STOP
 		 */
 		*bp++ = rd_byte(dd, !len);
 	}

 	ret = 0;

 bail:
 	return ret;
 }

 /*
  * qib_twsi_blk_wr
  * Formerly called qib_eeprom_internal_write, and only used for eeprom,
  * but now the general interface for data transfer to twsi devices.
  * One vestige of its former role is that it recognizes a device
  * QIB_TWSI_NO_DEV and does the correct operation for the legacy part,
  * which responded to all TWSI device codes, interpreting them as
  * address within device. On all other devices found on board handled by
  * this driver, the device is followed by a one-byte "address" which selects
  * the "register" or "offset" within the device to which data should
  * be written.
  */
 int qib_twsi_blk_wr(struct qib_devdata *dd, int dev, int addr,
 		    const void *buffer, int len)
 {
 	int sub_len;
 	const u8 *bp = buffer;
 	int max_wait_time, i;
 	int ret = 1;

 	while (len > 0) {
 		if (dev == QIB_TWSI_NO_DEV) {
 			if (qib_twsi_wr(dd, (addr << 1) | WRITE_CMD,
 					QIB_TWSI_START)) {
 				goto failed_write;
 			}
 		} else {
 			/* Real I2C */
 			if (qib_twsi_wr(dd, dev | WRITE_CMD, QIB_TWSI_START))
 				goto failed_write;
 			ret = qib_twsi_wr(dd, addr, 0);
 			if (ret) {
 				qib_dev_err(dd,
 					"Failed to write interface write addr %02X\n",
 					addr);
 				goto failed_write;
 			}
 		}

 		sub_len = min(len, 4);
 		addr += sub_len;
 		len -= sub_len;

 		for (i = 0; i < sub_len; i++)
 			if (qib_twsi_wr(dd, *bp++, 0))
 				goto failed_write;

 		stop_cmd(dd);

 		/*
 		 * Wait for write complete by waiting for a successful
 		 * read (the chip replies with a zero after the write
 		 * cmd completes, and before it writes to the eeprom.
 		 * The startcmd for the read will fail the ack until
 		 * the writes have completed.   We do this inline to avoid
 		 * the debug prints that are in the real read routine
 		 * if the startcmd fails.
 		 * We also use the proper device address, so it doesn't matter
 		 * whether we have real eeprom_dev. Legacy likes any address.
 		 */
 		max_wait_time = 100;
 		while (qib_twsi_wr(dd, dev | READ_CMD, QIB_TWSI_START)) {
 			stop_cmd(dd);
 			if (!--max_wait_time)
 				goto failed_write;
 		}
 		/* now read (and ignore) the resulting byte */
 		rd_byte(dd, 1);
 	}

 	ret = 0;
 	goto bail;

 failed_write:
 	stop_cmd(dd);
 	ret = 1;

 bail:
 	return ret;
 }
	/*
	* Copyright (c) 2012 Intel Corporation. All rights reserved.
	* Copyright (c) 2006 - 2012 QLogic Corporation. All rights reserved.
	* Copyright (c) 2003, 2004, 2005, 2006 PathScale, Inc. All rights reserved.
	*
	* This software is available to you under a choice of one of two
	* licenses. You may choose to be licensed under the terms of the GNU
	* General Public License (GPL) Version 2, available from the file
	* COPYING in the main directory of this source tree, or the
	* OpenIB.org BSD license below:
	*
	* Redistribution and use in source and binary forms, with or
	* without modification, are permitted provided that the following
	* conditions are met:
	*
	* - Redistributions of source code must retain the above
	* copyright notice, this list of conditions and the following
	* disclaimer.
	*
	* - Redistributions in binary form must reproduce the above
	* copyright notice, this list of conditions and the following
	* disclaimer in the documentation and/or other materials
	* provided with the distribution.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
	* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
	* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
	* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	* SOFTWARE.
	*/

	#include <linux/delay.h>
	#include <linux/pci.h>
	#include <linux/vmalloc.h>

	#include "qib.h"

	/*
	* QLogic_IB "Two Wire Serial Interface" driver.
	* Originally written for a not-quite-i2c serial eeprom, which is
	* still used on some supported boards. Later boards have added a
	* variety of other uses, most board-specific, so the bit-boffing
	* part has been split off to this file, while the other parts
	* have been moved to chip-specific files.
	*
	* We have also dropped all pretense of fully generic (e.g. pretend
	* we don't know whether '1' is the higher voltage) interface, as
	* the restrictions of the generic i2c interface (e.g. no access from
	* driver itself) make it unsuitable for this use.
	*/

	#define READ_CMD 1
	#define WRITE_CMD 0

	/**
	* i2c_wait_for_writes - wait for a write
	* @dd: the qlogic_ib device
	*
	* We use this instead of udelay directly, so we can make sure
	* that previous register writes have been flushed all the way
	* to the chip. Since we are delaying anyway, the cost doesn't
	* hurt, and makes the bit twiddling more regular
	*/
	static void i2c_wait_for_writes(struct qib_devdata *dd)
	{
	/*
	* implicit read of EXTStatus is as good as explicit
	* read of scratch, if all we want to do is flush
	* writes.
	*/
	dd->f_gpio_mod(dd, 0, 0, 0);
	rmb(); /* inlined, so prevent compiler reordering */
	}

	/*
	* QSFP modules are allowed to hold SCL low for 500uSec. Allow twice that
	* for "almost compliant" modules
	*/
	#define SCL_WAIT_USEC 1000

	/* BUF_WAIT is time bus must be free between STOP or ACK and to next START.
	* Should be 20, but some chips need more.
	*/
	#define TWSI_BUF_WAIT_USEC 60

	static void scl_out(struct qib_devdata *dd, u8 bit)
	{
	u32 mask;

	udelay(1);

	mask = 1UL << dd->gpio_scl_num;

	/* SCL is meant to be bare-drain, so never set "OUT", just DIR */
	dd->f_gpio_mod(dd, 0, bit ? 0 : mask, mask);

	/*
	* Allow for slow slaves by simple
	* delay for falling edge, sampling on rise.
	*/
	if (!bit)
	udelay(2);
	else {
	int rise_usec;

	for (rise_usec = SCL_WAIT_USEC; rise_usec > 0; rise_usec -= 2) {
	if (mask & dd->f_gpio_mod(dd, 0, 0, 0))
	break;
	udelay(2);
	}
	if (rise_usec <= 0)
	qib_dev_err(dd, "SCL interface stuck low > %d uSec\n",
	SCL_WAIT_USEC);
	}
	i2c_wait_for_writes(dd);
	}

	static void sda_out(struct qib_devdata *dd, u8 bit)
	{
	u32 mask;

	mask = 1UL << dd->gpio_sda_num;

	/* SDA is meant to be bare-drain, so never set "OUT", just DIR */
	dd->f_gpio_mod(dd, 0, bit ? 0 : mask, mask);

	i2c_wait_for_writes(dd);
	udelay(2);
	}

	static u8 sda_in(struct qib_devdata *dd, int wait)
	{
	int bnum;
	u32 read_val, mask;

	bnum = dd->gpio_sda_num;
	mask = (1UL << bnum);
	/* SDA is meant to be bare-drain, so never set "OUT", just DIR */
	dd->f_gpio_mod(dd, 0, 0, mask);
	read_val = dd->f_gpio_mod(dd, 0, 0, 0);
	if (wait)
	i2c_wait_for_writes(dd);
	return (read_val & mask) >> bnum;
	}

	/**
	* i2c_ackrcv - see if ack following write is true
	* @dd: the qlogic_ib device
	*/
	static int i2c_ackrcv(struct qib_devdata *dd)
	{
	u8 ack_received;

	/* AT ENTRY SCL = LOW */
	/* change direction, ignore data */
	ack_received = sda_in(dd, 1);
	scl_out(dd, 1);
	ack_received = sda_in(dd, 1) == 0;
	scl_out(dd, 0);
	return ack_received;
	}

	static void stop_cmd(struct qib_devdata *dd);

	/**
	* rd_byte - read a byte, sending STOP on last, else ACK
	* @dd: the qlogic_ib device
	*
	* Returns byte shifted out of device
	*/
	static int rd_byte(struct qib_devdata *dd, int last)
	{
	int bit_cntr, data;

	data = 0;

	for (bit_cntr = 7; bit_cntr >= 0; --bit_cntr) {
	data <<= 1;
	scl_out(dd, 1);
	data \|= sda_in(dd, 0);
	scl_out(dd, 0);
	}
	if (last) {
	scl_out(dd, 1);
	stop_cmd(dd);
	} else {
	sda_out(dd, 0);
	scl_out(dd, 1);
	scl_out(dd, 0);
	sda_out(dd, 1);
	}
	return data;
	}

	/**
	* wr_byte - write a byte, one bit at a time
	* @dd: the qlogic_ib device
	* @data: the byte to write
	*
	* Returns 0 if we got the following ack, otherwise 1
	*/
	static int wr_byte(struct qib_devdata *dd, u8 data)
	{
	int bit_cntr;
	u8 bit;

	for (bit_cntr = 7; bit_cntr >= 0; bit_cntr--) {
	bit = (data >> bit_cntr) & 1;
	sda_out(dd, bit);
	scl_out(dd, 1);
	scl_out(dd, 0);
	}
	return (!i2c_ackrcv(dd)) ? 1 : 0;
	}

	/*
	* issue TWSI start sequence:
	* (both clock/data high, clock high, data low while clock is high)
	*/
	static void start_seq(struct qib_devdata *dd)
	{
	sda_out(dd, 1);
	scl_out(dd, 1);
	sda_out(dd, 0);
	udelay(1);
	scl_out(dd, 0);
	}

	/**
	* stop_seq - transmit the stop sequence
	* @dd: the qlogic_ib device
	*
	* (both clock/data low, clock high, data high while clock is high)
	*/
	static void stop_seq(struct qib_devdata *dd)
	{
	scl_out(dd, 0);
	sda_out(dd, 0);
	scl_out(dd, 1);
	sda_out(dd, 1);
	}

	/**
	* stop_cmd - transmit the stop condition
	* @dd: the qlogic_ib device
	*
	* (both clock/data low, clock high, data high while clock is high)
	*/
	static void stop_cmd(struct qib_devdata *dd)
	{
	stop_seq(dd);
	udelay(TWSI_BUF_WAIT_USEC);
	}

	/**
	* qib_twsi_reset - reset I2C communication
	* @dd: the qlogic_ib device
	*/

	int qib_twsi_reset(struct qib_devdata *dd)
	{
	int clock_cycles_left = 9;
	int was_high = 0;
	u32 pins, mask;

	/* Both SCL and SDA should be high. If not, there
	* is something wrong.
	*/
	mask = (1UL << dd->gpio_scl_num) \| (1UL << dd->gpio_sda_num);

	/*
	* Force pins to desired innocuous state.
	* This is the default power-on state with out=0 and dir=0,
	* So tri-stated and should be floating high (barring HW problems)
	*/
	dd->f_gpio_mod(dd, 0, 0, mask);

	/*
	* Clock nine times to get all listeners into a sane state.
	* If SDA does not go high at any point, we are wedged.
	* One vendor recommends then issuing START followed by STOP.
	* we cannot use our "normal" functions to do that, because
	* if SCL drops between them, another vendor's part will
	* wedge, dropping SDA and keeping it low forever, at the end of
	* the next transaction (even if it was not the device addressed).
	* So our START and STOP take place with SCL held high.
	*/
	while (clock_cycles_left--) {
	scl_out(dd, 0);
	scl_out(dd, 1);
	/* Note if SDA is high, but keep clocking to sync slave */
	was_high \|= sda_in(dd, 0);
	}

	if (was_high) {
	/*
	* We saw a high, which we hope means the slave is sync'd.
	* Issue START, STOP, pause for T_BUF.
	*/

	pins = dd->f_gpio_mod(dd, 0, 0, 0);
	if ((pins & mask) != mask)
	qib_dev_err(dd, "GPIO pins not at rest: %d\n",
	pins & mask);
	/* Drop SDA to issue START */
	udelay(1); /* Guarantee .6 uSec setup */
	sda_out(dd, 0);
	udelay(1); /* Guarantee .6 uSec hold */
	/* At this point, SCL is high, SDA low. Raise SDA for STOP */
	sda_out(dd, 1);
	udelay(TWSI_BUF_WAIT_USEC);
	}

	return !was_high;
	}

	#define QIB_TWSI_START 0x100
	#define QIB_TWSI_STOP 0x200

	/* Write byte to TWSI, optionally prefixed with START or suffixed with
	* STOP.
	* returns 0 if OK (ACK received), else != 0
	*/
	static int qib_twsi_wr(struct qib_devdata *dd, int data, int flags)
	{
	int ret = 1;

	if (flags & QIB_TWSI_START)
	start_seq(dd);

	ret = wr_byte(dd, data); /* Leaves SCL low (from i2c_ackrcv()) */

	if (flags & QIB_TWSI_STOP)
	stop_cmd(dd);
	return ret;
	}

	/* Added functionality for IBA7220-based cards */
	#define QIB_TEMP_DEV 0x98

	/*
	* qib_twsi_blk_rd
	* Formerly called qib_eeprom_internal_read, and only used for eeprom,
	* but now the general interface for data transfer from twsi devices.
	* One vestige of its former role is that it recognizes a device
	* QIB_TWSI_NO_DEV and does the correct operation for the legacy part,
	* which responded to all TWSI device codes, interpreting them as
	* address within device. On all other devices found on board handled by
	* this driver, the device is followed by a one-byte "address" which selects
	* the "register" or "offset" within the device from which data should
	* be read.
	*/
	int qib_twsi_blk_rd(struct qib_devdata *dd, int dev, int addr,
	void *buffer, int len)
	{
	int ret;
	u8 *bp = buffer;

	ret = 1;

	if (dev == QIB_TWSI_NO_DEV) {
	/* legacy not-really-I2C */
	addr = (addr << 1) \| READ_CMD;
	ret = qib_twsi_wr(dd, addr, QIB_TWSI_START);
	} else {
	/* Actual I2C */
	ret = qib_twsi_wr(dd, dev \| WRITE_CMD, QIB_TWSI_START);
	if (ret) {
	stop_cmd(dd);
	ret = 1;
	goto bail;
	}
	/*
	* SFF spec claims we do _not_ stop after the addr
	* but simply issue a start with the "read" dev-addr.
	* Since we are implicitely waiting for ACK here,
	* we need t_buf (nominally 20uSec) before that start,
	* and cannot rely on the delay built in to the STOP
	*/
	ret = qib_twsi_wr(dd, addr, 0);
	udelay(TWSI_BUF_WAIT_USEC);

	if (ret) {
	qib_dev_err(dd,
	"Failed to write interface read addr %02X\n",
	addr);
	ret = 1;
	goto bail;
	}
	ret = qib_twsi_wr(dd, dev \| READ_CMD, QIB_TWSI_START);
	}
	if (ret) {
	stop_cmd(dd);
	ret = 1;
	goto bail;
	}

	/*
	* block devices keeps clocking data out as long as we ack,
	* automatically incrementing the address. Some have "pages"
	* whose boundaries will not be crossed, but the handling
	* of these is left to the caller, who is in a better
	* position to know.
	*/
	while (len-- > 0) {
	/*
	* Get and store data, sending ACK if length remaining,
	* else STOP
	*/
	*bp++ = rd_byte(dd, !len);
	}

	ret = 0;

	bail:
	return ret;
	}

	/*
	* qib_twsi_blk_wr
	* Formerly called qib_eeprom_internal_write, and only used for eeprom,
	* but now the general interface for data transfer to twsi devices.
	* One vestige of its former role is that it recognizes a device
	* QIB_TWSI_NO_DEV and does the correct operation for the legacy part,
	* which responded to all TWSI device codes, interpreting them as
	* address within device. On all other devices found on board handled by
	* this driver, the device is followed by a one-byte "address" which selects
	* the "register" or "offset" within the device to which data should
	* be written.
	*/
	int qib_twsi_blk_wr(struct qib_devdata *dd, int dev, int addr,
	const void *buffer, int len)
	{
	int sub_len;
	const u8 *bp = buffer;
	int max_wait_time, i;
	int ret = 1;

	while (len > 0) {
	if (dev == QIB_TWSI_NO_DEV) {
	if (qib_twsi_wr(dd, (addr << 1) \| WRITE_CMD,
	QIB_TWSI_START)) {
	goto failed_write;
	}
	} else {
	/* Real I2C */
	if (qib_twsi_wr(dd, dev \| WRITE_CMD, QIB_TWSI_START))
	goto failed_write;
	ret = qib_twsi_wr(dd, addr, 0);
	if (ret) {
	qib_dev_err(dd,
	"Failed to write interface write addr %02X\n",
	addr);
	goto failed_write;
	}
	}

	sub_len = min(len, 4);
	addr += sub_len;
	len -= sub_len;

	for (i = 0; i < sub_len; i++)
	if (qib_twsi_wr(dd, *bp++, 0))
	goto failed_write;

	stop_cmd(dd);

	/*
	* Wait for write complete by waiting for a successful
	* read (the chip replies with a zero after the write
	* cmd completes, and before it writes to the eeprom.
	* The startcmd for the read will fail the ack until
	* the writes have completed. We do this inline to avoid
	* the debug prints that are in the real read routine
	* if the startcmd fails.
	* We also use the proper device address, so it doesn't matter
	* whether we have real eeprom_dev. Legacy likes any address.
	*/
	max_wait_time = 100;
	while (qib_twsi_wr(dd, dev \| READ_CMD, QIB_TWSI_START)) {
	stop_cmd(dd);
	if (!--max_wait_time)
	goto failed_write;
	}
	/* now read (and ignore) the resulting byte */
	rd_byte(dd, 1);
	}

	ret = 0;
	goto bail;

	failed_write:
	stop_cmd(dd);
	ret = 1;

	bail:
	return ret;
	}