drivers/tpm/tpm_tis_lpc.c - filogic/uboot - Gitiles

 /*
  * Copyright (c) 2011 The Chromium OS Authors.
  *
  * SPDX-License-Identifier:	GPL-2.0+
  */

 /*
  * The code in this file is based on the article "Writing a TPM Device Driver"
  * published on http://ptgmedia.pearsoncmg.com.
  *
  * One principal difference is that in the simplest config the other than 0
  * TPM localities do not get mapped by some devices (for instance, by Infineon
  * slb9635), so this driver provides access to locality 0 only.
  */

 #include <common.h>
 #include <asm/io.h>
 #include <tis.h>
 #include <tpm.h>

 #define PREFIX "lpc_tpm: "

 struct tpm_locality {
 	u32 access;
 	u8 padding0[4];
 	u32 int_enable;
 	u8 vector;
 	u8 padding1[3];
 	u32 int_status;
 	u32 int_capability;
 	u32 tpm_status;
 	u8 padding2[8];
 	u8 data;
 	u8 padding3[3803];
 	u32 did_vid;
 	u8 rid;
 	u8 padding4[251];
 };

 /*
  * This pointer refers to the TPM chip, 5 of its localities are mapped as an
  * array.
  */
 #define TPM_TOTAL_LOCALITIES	5
 static struct tpm_locality *lpc_tpm_dev =
 	(struct tpm_locality *)CONFIG_TPM_TIS_BASE_ADDRESS;

 /* Some registers' bit field definitions */
 #define TIS_STS_VALID                  (1 << 7) /* 0x80 */
 #define TIS_STS_COMMAND_READY          (1 << 6) /* 0x40 */
 #define TIS_STS_TPM_GO                 (1 << 5) /* 0x20 */
 #define TIS_STS_DATA_AVAILABLE         (1 << 4) /* 0x10 */
 #define TIS_STS_EXPECT                 (1 << 3) /* 0x08 */
 #define TIS_STS_RESPONSE_RETRY         (1 << 1) /* 0x02 */

 #define TIS_ACCESS_TPM_REG_VALID_STS   (1 << 7) /* 0x80 */
 #define TIS_ACCESS_ACTIVE_LOCALITY     (1 << 5) /* 0x20 */
 #define TIS_ACCESS_BEEN_SEIZED         (1 << 4) /* 0x10 */
 #define TIS_ACCESS_SEIZE               (1 << 3) /* 0x08 */
 #define TIS_ACCESS_PENDING_REQUEST     (1 << 2) /* 0x04 */
 #define TIS_ACCESS_REQUEST_USE         (1 << 1) /* 0x02 */
 #define TIS_ACCESS_TPM_ESTABLISHMENT   (1 << 0) /* 0x01 */

 #define TIS_STS_BURST_COUNT_MASK       (0xffff)
 #define TIS_STS_BURST_COUNT_SHIFT      (8)

 /*
  * Error value returned if a tpm register does not enter the expected state
  * after continuous polling. No actual TPM register reading ever returns -1,
  * so this value is a safe error indication to be mixed with possible status
  * register values.
  */
 #define TPM_TIMEOUT_ERR			(-1)

 /* Error value returned on various TPM driver errors. */
 #define TPM_DRIVER_ERR		(1)

  /* 1 second is plenty for anything TPM does. */
 #define MAX_DELAY_US	(1000 * 1000)

 /* Retrieve burst count value out of the status register contents. */
 static u16 burst_count(u32 status)
 {
 	return (status >> TIS_STS_BURST_COUNT_SHIFT) & TIS_STS_BURST_COUNT_MASK;
 }

 /*
  * Structures defined below allow creating descriptions of TPM vendor/device
  * ID information for run time discovery. The only device the system knows
  * about at this time is Infineon slb9635.
  */
 struct device_name {
 	u16 dev_id;
 	const char * const dev_name;
 };

 struct vendor_name {
 	u16 vendor_id;
 	const char *vendor_name;
 	const struct device_name *dev_names;
 };

 static const struct device_name infineon_devices[] = {
 	{0xb, "SLB9635 TT 1.2"},
 	{0}
 };

 static const struct vendor_name vendor_names[] = {
 	{0x15d1, "Infineon", infineon_devices},
 };

 /*
  * Cached vendor/device ID pair to indicate that the device has been already
  * discovered.
  */
 static u32 vendor_dev_id;

 /* TPM access wrappers to support tracing */
 static u8 tpm_read_byte(const u8 *ptr)
 {
 	u8  ret = readb(ptr);
 	debug(PREFIX "Read reg 0x%4.4x returns 0x%2.2x\n",
 	      (u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, ret);
 	return ret;
 }

 static u32 tpm_read_word(const u32 *ptr)
 {
 	u32  ret = readl(ptr);
 	debug(PREFIX "Read reg 0x%4.4x returns 0x%8.8x\n",
 	      (u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, ret);
 	return ret;
 }

 static void tpm_write_byte(u8 value, u8 *ptr)
 {
 	debug(PREFIX "Write reg 0x%4.4x with 0x%2.2x\n",
 	      (u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, value);
 	writeb(value, ptr);
 }

 static void tpm_write_word(u32 value, u32 *ptr)
 {
 	debug(PREFIX "Write reg 0x%4.4x with 0x%8.8x\n",
 	      (u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, value);
 	writel(value, ptr);
 }

 /*
  * tis_wait_reg()
  *
  * Wait for at least a second for a register to change its state to match the
  * expected state. Normally the transition happens within microseconds.
  *
  * @reg - pointer to the TPM register
  * @mask - bitmask for the bitfield(s) to watch
  * @expected - value the field(s) are supposed to be set to
  *
  * Returns the register contents in case the expected value was found in the
  * appropriate register bits, or TPM_TIMEOUT_ERR on timeout.
  */
 static u32 tis_wait_reg(u32 *reg, u8 mask, u8 expected)
 {
 	u32 time_us = MAX_DELAY_US;

 	while (time_us > 0) {
 		u32 value = tpm_read_word(reg);
 		if ((value & mask) == expected)
 			return value;
 		udelay(1); /* 1 us */
 		time_us--;
 	}
 	return TPM_TIMEOUT_ERR;
 }

 /*
  * Probe the TPM device and try determining its manufacturer/device name.
  *
  * Returns 0 on success (the device is found or was found during an earlier
  * invocation) or TPM_DRIVER_ERR if the device is not found.
  */
 int tis_init(void)
 {
 	u32 didvid = tpm_read_word(&lpc_tpm_dev[0].did_vid);
 	int i;
 	const char *device_name = "unknown";
 	const char *vendor_name = device_name;
 	u16 vid, did;

 	if (vendor_dev_id)
 		return 0;  /* Already probed. */

 	if (!didvid || (didvid == 0xffffffff)) {
 		printf("%s: No TPM device found\n", __func__);
 		return TPM_DRIVER_ERR;
 	}

 	vendor_dev_id = didvid;

 	vid = didvid & 0xffff;
 	did = (didvid >> 16) & 0xffff;
 	for (i = 0; i < ARRAY_SIZE(vendor_names); i++) {
 		int j = 0;
 		u16 known_did;

 		if (vid == vendor_names[i].vendor_id)
 			vendor_name = vendor_names[i].vendor_name;

 		while ((known_did = vendor_names[i].dev_names[j].dev_id) != 0) {
 			if (known_did == did) {
 				device_name =
 					vendor_names[i].dev_names[j].dev_name;
 				break;
 			}
 			j++;
 		}
 		break;
 	}

 	printf("Found TPM %s by %s\n", device_name, vendor_name);
 	return 0;
 }

 /*
  * tis_senddata()
  *
  * send the passed in data to the TPM device.
  *
  * @data - address of the data to send, byte by byte
  * @len - length of the data to send
  *
  * Returns 0 on success, TPM_DRIVER_ERR on error (in case the device does
  * not accept the entire command).
  */
 static u32 tis_senddata(const u8 * const data, u32 len)
 {
 	u32 offset = 0;
 	u16 burst = 0;
 	u32 max_cycles = 0;
 	u8 locality = 0;
 	u32 value;

 	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
 			     TIS_STS_COMMAND_READY, TIS_STS_COMMAND_READY);
 	if (value == TPM_TIMEOUT_ERR) {
 		printf("%s:%d - failed to get 'command_ready' status\n",
 		       __FILE__, __LINE__);
 		return TPM_DRIVER_ERR;
 	}
 	burst = burst_count(value);

 	while (1) {
 		unsigned count;

 		/* Wait till the device is ready to accept more data. */
 		while (!burst) {
 			if (max_cycles++ == MAX_DELAY_US) {
 				printf("%s:%d failed to feed %d bytes of %d\n",
 				       __FILE__, __LINE__, len - offset, len);
 				return TPM_DRIVER_ERR;
 			}
 			udelay(1);
 			burst = burst_count(tpm_read_word(&lpc_tpm_dev
 						     [locality].tpm_status));
 		}

 		max_cycles = 0;

 		/*
 		 * Calculate number of bytes the TPM is ready to accept in one
 		 * shot.
 		 *
 		 * We want to send the last byte outside of the loop (hence
 		 * the -1 below) to make sure that the 'expected' status bit
 		 * changes to zero exactly after the last byte is fed into the
 		 * FIFO.
 		 */
 		count = min((u32)burst, len - offset - 1);
 		while (count--)
 			tpm_write_byte(data[offset++],
 				  &lpc_tpm_dev[locality].data);

 		value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
 				     TIS_STS_VALID, TIS_STS_VALID);

 		if ((value == TPM_TIMEOUT_ERR) || !(value & TIS_STS_EXPECT)) {
 			printf("%s:%d TPM command feed overflow\n",
 			       __FILE__, __LINE__);
 			return TPM_DRIVER_ERR;
 		}

 		burst = burst_count(value);
 		if ((offset == (len - 1)) && burst) {
 			/*
 			 * We need to be able to send the last byte to the
 			 * device, so burst size must be nonzero before we
 			 * break out.
 			 */
 			break;
 		}
 	}

 	/* Send the last byte. */
 	tpm_write_byte(data[offset++], &lpc_tpm_dev[locality].data);
 	/*
 	 * Verify that TPM does not expect any more data as part of this
 	 * command.
 	 */
 	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
 			     TIS_STS_VALID, TIS_STS_VALID);
 	if ((value == TPM_TIMEOUT_ERR) || (value & TIS_STS_EXPECT)) {
 		printf("%s:%d unexpected TPM status 0x%x\n",
 		       __FILE__, __LINE__, value);
 		return TPM_DRIVER_ERR;
 	}

 	/* OK, sitting pretty, let's start the command execution. */
 	tpm_write_word(TIS_STS_TPM_GO, &lpc_tpm_dev[locality].tpm_status);
 	return 0;
 }

 /*
  * tis_readresponse()
  *
  * read the TPM device response after a command was issued.
  *
  * @buffer - address where to read the response, byte by byte.
  * @len - pointer to the size of buffer
  *
  * On success stores the number of received bytes to len and returns 0. On
  * errors (misformatted TPM data or synchronization problems) returns
  * TPM_DRIVER_ERR.
  */
 static u32 tis_readresponse(u8 *buffer, u32 *len)
 {
 	u16 burst;
 	u32 value;
 	u32 offset = 0;
 	u8 locality = 0;
 	const u32 has_data = TIS_STS_DATA_AVAILABLE | TIS_STS_VALID;
 	u32 expected_count = *len;
 	int max_cycles = 0;

 	/* Wait for the TPM to process the command. */
 	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
 			      has_data, has_data);
 	if (value == TPM_TIMEOUT_ERR) {
 		printf("%s:%d failed processing command\n",
 		       __FILE__, __LINE__);
 		return TPM_DRIVER_ERR;
 	}

 	do {
 		while ((burst = burst_count(value)) == 0) {
 			if (max_cycles++ == MAX_DELAY_US) {
 				printf("%s:%d TPM stuck on read\n",
 				       __FILE__, __LINE__);
 				return TPM_DRIVER_ERR;
 			}
 			udelay(1);
 			value = tpm_read_word(&lpc_tpm_dev
 					      [locality].tpm_status);
 		}

 		max_cycles = 0;

 		while (burst-- && (offset < expected_count)) {
 			buffer[offset++] = tpm_read_byte(&lpc_tpm_dev
 							 [locality].data);

 			if (offset == 6) {
 				/*
 				 * We got the first six bytes of the reply,
 				 * let's figure out how many bytes to expect
 				 * total - it is stored as a 4 byte number in
 				 * network order, starting with offset 2 into
 				 * the body of the reply.
 				 */
 				u32 real_length;
 				memcpy(&real_length,
 				       buffer + 2,
 				       sizeof(real_length));
 				expected_count = be32_to_cpu(real_length);

 				if ((expected_count < offset) ||
 				    (expected_count > *len)) {
 					printf("%s:%d bad response size %d\n",
 					       __FILE__, __LINE__,
 					       expected_count);
 					return TPM_DRIVER_ERR;
 				}
 			}
 		}

 		/* Wait for the next portion. */
 		value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
 				     TIS_STS_VALID, TIS_STS_VALID);
 		if (value == TPM_TIMEOUT_ERR) {
 			printf("%s:%d failed to read response\n",
 			       __FILE__, __LINE__);
 			return TPM_DRIVER_ERR;
 		}

 		if (offset == expected_count)
 			break;	/* We got all we needed. */

 	} while ((value & has_data) == has_data);

 	/*
 	 * Make sure we indeed read all there was. The TIS_STS_VALID bit is
 	 * known to be set.
 	 */
 	if (value & TIS_STS_DATA_AVAILABLE) {
 		printf("%s:%d wrong receive status %x\n",
 		       __FILE__, __LINE__, value);
 		return TPM_DRIVER_ERR;
 	}

 	/* Tell the TPM that we are done. */
 	tpm_write_word(TIS_STS_COMMAND_READY, &lpc_tpm_dev
 		  [locality].tpm_status);
 	*len = offset;
 	return 0;
 }

 int tis_open(void)
 {
 	u8 locality = 0; /* we use locality zero for everything. */

 	/* now request access to locality. */
 	tpm_write_word(TIS_ACCESS_REQUEST_USE, &lpc_tpm_dev[locality].access);

 	/* did we get a lock? */
 	if (tis_wait_reg(&lpc_tpm_dev[locality].access,
 			 TIS_ACCESS_ACTIVE_LOCALITY,
 			 TIS_ACCESS_ACTIVE_LOCALITY) == TPM_TIMEOUT_ERR) {
 		printf("%s:%d - failed to lock locality %d\n",
 		       __FILE__, __LINE__, locality);
 		return TPM_DRIVER_ERR;
 	}

 	tpm_write_word(TIS_STS_COMMAND_READY,
 		       &lpc_tpm_dev[locality].tpm_status);
 	return 0;
 }

 int tis_close(void)
 {
 	u8 locality = 0;

 	if (tpm_read_word(&lpc_tpm_dev[locality].access) &
 	    TIS_ACCESS_ACTIVE_LOCALITY) {
 		tpm_write_word(TIS_ACCESS_ACTIVE_LOCALITY,
 			       &lpc_tpm_dev[locality].access);

 		if (tis_wait_reg(&lpc_tpm_dev[locality].access,
 				 TIS_ACCESS_ACTIVE_LOCALITY, 0) ==
 		    TPM_TIMEOUT_ERR) {
 			printf("%s:%d - failed to release locality %d\n",
 			       __FILE__, __LINE__, locality);
 			return TPM_DRIVER_ERR;
 		}
 	}
 	return 0;
 }

 int tis_sendrecv(const u8 *sendbuf, size_t send_size,
 		 u8 *recvbuf, size_t *recv_len)
 {
 	if (tis_senddata(sendbuf, send_size)) {
 		printf("%s:%d failed sending data to TPM\n",
 		       __FILE__, __LINE__);
 		return TPM_DRIVER_ERR;
 	}

 	return tis_readresponse(recvbuf, (u32 *)recv_len);
 }
	/*
	* Copyright (c) 2011 The Chromium OS Authors.
	*
	* SPDX-License-Identifier: GPL-2.0+
	*/

	/*
	* The code in this file is based on the article "Writing a TPM Device Driver"
	* published on http://ptgmedia.pearsoncmg.com.
	*
	* One principal difference is that in the simplest config the other than 0
	* TPM localities do not get mapped by some devices (for instance, by Infineon
	* slb9635), so this driver provides access to locality 0 only.
	*/

	#include <common.h>
	#include <asm/io.h>
	#include <tis.h>
	#include <tpm.h>

	#define PREFIX "lpc_tpm: "

	struct tpm_locality {
	u32 access;
	u8 padding0[4];
	u32 int_enable;
	u8 vector;
	u8 padding1[3];
	u32 int_status;
	u32 int_capability;
	u32 tpm_status;
	u8 padding2[8];
	u8 data;
	u8 padding3[3803];
	u32 did_vid;
	u8 rid;
	u8 padding4[251];
	};

	/*
	* This pointer refers to the TPM chip, 5 of its localities are mapped as an
	* array.
	*/
	#define TPM_TOTAL_LOCALITIES 5
	static struct tpm_locality *lpc_tpm_dev =
	(struct tpm_locality *)CONFIG_TPM_TIS_BASE_ADDRESS;

	/* Some registers' bit field definitions */
	#define TIS_STS_VALID (1 << 7) /* 0x80 */
	#define TIS_STS_COMMAND_READY (1 << 6) /* 0x40 */
	#define TIS_STS_TPM_GO (1 << 5) /* 0x20 */
	#define TIS_STS_DATA_AVAILABLE (1 << 4) /* 0x10 */
	#define TIS_STS_EXPECT (1 << 3) /* 0x08 */
	#define TIS_STS_RESPONSE_RETRY (1 << 1) /* 0x02 */

	#define TIS_ACCESS_TPM_REG_VALID_STS (1 << 7) /* 0x80 */
	#define TIS_ACCESS_ACTIVE_LOCALITY (1 << 5) /* 0x20 */
	#define TIS_ACCESS_BEEN_SEIZED (1 << 4) /* 0x10 */
	#define TIS_ACCESS_SEIZE (1 << 3) /* 0x08 */
	#define TIS_ACCESS_PENDING_REQUEST (1 << 2) /* 0x04 */
	#define TIS_ACCESS_REQUEST_USE (1 << 1) /* 0x02 */
	#define TIS_ACCESS_TPM_ESTABLISHMENT (1 << 0) /* 0x01 */

	#define TIS_STS_BURST_COUNT_MASK (0xffff)
	#define TIS_STS_BURST_COUNT_SHIFT (8)

	/*
	* Error value returned if a tpm register does not enter the expected state
	* after continuous polling. No actual TPM register reading ever returns -1,
	* so this value is a safe error indication to be mixed with possible status
	* register values.
	*/
	#define TPM_TIMEOUT_ERR (-1)

	/* Error value returned on various TPM driver errors. */
	#define TPM_DRIVER_ERR (1)

	/* 1 second is plenty for anything TPM does. */
	#define MAX_DELAY_US (1000 * 1000)

	/* Retrieve burst count value out of the status register contents. */
	static u16 burst_count(u32 status)
	{
	return (status >> TIS_STS_BURST_COUNT_SHIFT) & TIS_STS_BURST_COUNT_MASK;
	}

	/*
	* Structures defined below allow creating descriptions of TPM vendor/device
	* ID information for run time discovery. The only device the system knows
	* about at this time is Infineon slb9635.
	*/
	struct device_name {
	u16 dev_id;
	const char * const dev_name;
	};

	struct vendor_name {
	u16 vendor_id;
	const char *vendor_name;
	const struct device_name *dev_names;
	};

	static const struct device_name infineon_devices[] = {
	{0xb, "SLB9635 TT 1.2"},
	{0}
	};

	static const struct vendor_name vendor_names[] = {
	{0x15d1, "Infineon", infineon_devices},
	};

	/*
	* Cached vendor/device ID pair to indicate that the device has been already
	* discovered.
	*/
	static u32 vendor_dev_id;

	/* TPM access wrappers to support tracing */
	static u8 tpm_read_byte(const u8 *ptr)
	{
	u8 ret = readb(ptr);
	debug(PREFIX "Read reg 0x%4.4x returns 0x%2.2x\n",
	(u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, ret);
	return ret;
	}

	static u32 tpm_read_word(const u32 *ptr)
	{
	u32 ret = readl(ptr);
	debug(PREFIX "Read reg 0x%4.4x returns 0x%8.8x\n",
	(u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, ret);
	return ret;
	}

	static void tpm_write_byte(u8 value, u8 *ptr)
	{
	debug(PREFIX "Write reg 0x%4.4x with 0x%2.2x\n",
	(u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, value);
	writeb(value, ptr);
	}

	static void tpm_write_word(u32 value, u32 *ptr)
	{
	debug(PREFIX "Write reg 0x%4.4x with 0x%8.8x\n",
	(u32)(uintptr_t)ptr - (u32)(uintptr_t)lpc_tpm_dev, value);
	writel(value, ptr);
	}

	/*
	* tis_wait_reg()
	*
	* Wait for at least a second for a register to change its state to match the
	* expected state. Normally the transition happens within microseconds.
	*
	* @reg - pointer to the TPM register
	* @mask - bitmask for the bitfield(s) to watch
	* @expected - value the field(s) are supposed to be set to
	*
	* Returns the register contents in case the expected value was found in the
	* appropriate register bits, or TPM_TIMEOUT_ERR on timeout.
	*/
	static u32 tis_wait_reg(u32 *reg, u8 mask, u8 expected)
	{
	u32 time_us = MAX_DELAY_US;

	while (time_us > 0) {
	u32 value = tpm_read_word(reg);
	if ((value & mask) == expected)
	return value;
	udelay(1); /* 1 us */
	time_us--;
	}
	return TPM_TIMEOUT_ERR;
	}

	/*
	* Probe the TPM device and try determining its manufacturer/device name.
	*
	* Returns 0 on success (the device is found or was found during an earlier
	* invocation) or TPM_DRIVER_ERR if the device is not found.
	*/
	int tis_init(void)
	{
	u32 didvid = tpm_read_word(&lpc_tpm_dev[0].did_vid);
	int i;
	const char *device_name = "unknown";
	const char *vendor_name = device_name;
	u16 vid, did;

	if (vendor_dev_id)
	return 0; /* Already probed. */

	if (!didvid \|\| (didvid == 0xffffffff)) {
	printf("%s: No TPM device found\n", __func__);
	return TPM_DRIVER_ERR;
	}

	vendor_dev_id = didvid;

	vid = didvid & 0xffff;
	did = (didvid >> 16) & 0xffff;
	for (i = 0; i < ARRAY_SIZE(vendor_names); i++) {
	int j = 0;
	u16 known_did;

	if (vid == vendor_names[i].vendor_id)
	vendor_name = vendor_names[i].vendor_name;

	while ((known_did = vendor_names[i].dev_names[j].dev_id) != 0) {
	if (known_did == did) {
	device_name =
	vendor_names[i].dev_names[j].dev_name;
	break;
	}
	j++;
	}
	break;
	}

	printf("Found TPM %s by %s\n", device_name, vendor_name);
	return 0;
	}

	/*
	* tis_senddata()
	*
	* send the passed in data to the TPM device.
	*
	* @data - address of the data to send, byte by byte
	* @len - length of the data to send
	*
	* Returns 0 on success, TPM_DRIVER_ERR on error (in case the device does
	* not accept the entire command).
	*/
	static u32 tis_senddata(const u8 * const data, u32 len)
	{
	u32 offset = 0;
	u16 burst = 0;
	u32 max_cycles = 0;
	u8 locality = 0;
	u32 value;

	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
	TIS_STS_COMMAND_READY, TIS_STS_COMMAND_READY);
	if (value == TPM_TIMEOUT_ERR) {
	printf("%s:%d - failed to get 'command_ready' status\n",
	__FILE__, __LINE__);
	return TPM_DRIVER_ERR;
	}
	burst = burst_count(value);

	while (1) {
	unsigned count;

	/* Wait till the device is ready to accept more data. */
	while (!burst) {
	if (max_cycles++ == MAX_DELAY_US) {
	printf("%s:%d failed to feed %d bytes of %d\n",
	__FILE__, __LINE__, len - offset, len);
	return TPM_DRIVER_ERR;
	}
	udelay(1);
	burst = burst_count(tpm_read_word(&lpc_tpm_dev
	[locality].tpm_status));
	}

	max_cycles = 0;

	/*
	* Calculate number of bytes the TPM is ready to accept in one
	* shot.
	*
	* We want to send the last byte outside of the loop (hence
	* the -1 below) to make sure that the 'expected' status bit
	* changes to zero exactly after the last byte is fed into the
	* FIFO.
	*/
	count = min((u32)burst, len - offset - 1);
	while (count--)
	tpm_write_byte(data[offset++],
	&lpc_tpm_dev[locality].data);

	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
	TIS_STS_VALID, TIS_STS_VALID);

	if ((value == TPM_TIMEOUT_ERR) \|\| !(value & TIS_STS_EXPECT)) {
	printf("%s:%d TPM command feed overflow\n",
	__FILE__, __LINE__);
	return TPM_DRIVER_ERR;
	}

	burst = burst_count(value);
	if ((offset == (len - 1)) && burst) {
	/*
	* We need to be able to send the last byte to the
	* device, so burst size must be nonzero before we
	* break out.
	*/
	break;
	}
	}

	/* Send the last byte. */
	tpm_write_byte(data[offset++], &lpc_tpm_dev[locality].data);
	/*
	* Verify that TPM does not expect any more data as part of this
	* command.
	*/
	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
	TIS_STS_VALID, TIS_STS_VALID);
	if ((value == TPM_TIMEOUT_ERR) \|\| (value & TIS_STS_EXPECT)) {
	printf("%s:%d unexpected TPM status 0x%x\n",
	__FILE__, __LINE__, value);
	return TPM_DRIVER_ERR;
	}

	/* OK, sitting pretty, let's start the command execution. */
	tpm_write_word(TIS_STS_TPM_GO, &lpc_tpm_dev[locality].tpm_status);
	return 0;
	}

	/*
	* tis_readresponse()
	*
	* read the TPM device response after a command was issued.
	*
	* @buffer - address where to read the response, byte by byte.
	* @len - pointer to the size of buffer
	*
	* On success stores the number of received bytes to len and returns 0. On
	* errors (misformatted TPM data or synchronization problems) returns
	* TPM_DRIVER_ERR.
	*/
	static u32 tis_readresponse(u8 buffer, u32 len)
	{
	u16 burst;
	u32 value;
	u32 offset = 0;
	u8 locality = 0;
	const u32 has_data = TIS_STS_DATA_AVAILABLE \| TIS_STS_VALID;
	u32 expected_count = *len;
	int max_cycles = 0;

	/* Wait for the TPM to process the command. */
	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
	has_data, has_data);
	if (value == TPM_TIMEOUT_ERR) {
	printf("%s:%d failed processing command\n",
	__FILE__, __LINE__);
	return TPM_DRIVER_ERR;
	}

	do {
	while ((burst = burst_count(value)) == 0) {
	if (max_cycles++ == MAX_DELAY_US) {
	printf("%s:%d TPM stuck on read\n",
	__FILE__, __LINE__);
	return TPM_DRIVER_ERR;
	}
	udelay(1);
	value = tpm_read_word(&lpc_tpm_dev
	[locality].tpm_status);
	}

	max_cycles = 0;

	while (burst-- && (offset < expected_count)) {
	buffer[offset++] = tpm_read_byte(&lpc_tpm_dev
	[locality].data);

	if (offset == 6) {
	/*
	* We got the first six bytes of the reply,
	* let's figure out how many bytes to expect
	* total - it is stored as a 4 byte number in
	* network order, starting with offset 2 into
	* the body of the reply.
	*/
	u32 real_length;
	memcpy(&real_length,
	buffer + 2,
	sizeof(real_length));
	expected_count = be32_to_cpu(real_length);

	if ((expected_count < offset) \|\|
	(expected_count > *len)) {
	printf("%s:%d bad response size %d\n",
	__FILE__, __LINE__,
	expected_count);
	return TPM_DRIVER_ERR;
	}
	}
	}

	/* Wait for the next portion. */
	value = tis_wait_reg(&lpc_tpm_dev[locality].tpm_status,
	TIS_STS_VALID, TIS_STS_VALID);
	if (value == TPM_TIMEOUT_ERR) {
	printf("%s:%d failed to read response\n",
	__FILE__, __LINE__);
	return TPM_DRIVER_ERR;
	}

	if (offset == expected_count)
	break; /* We got all we needed. */

	} while ((value & has_data) == has_data);

	/*
	* Make sure we indeed read all there was. The TIS_STS_VALID bit is
	* known to be set.
	*/
	if (value & TIS_STS_DATA_AVAILABLE) {
	printf("%s:%d wrong receive status %x\n",
	__FILE__, __LINE__, value);
	return TPM_DRIVER_ERR;
	}

	/* Tell the TPM that we are done. */
	tpm_write_word(TIS_STS_COMMAND_READY, &lpc_tpm_dev
	[locality].tpm_status);
	*len = offset;
	return 0;
	}

	int tis_open(void)
	{
	u8 locality = 0; /* we use locality zero for everything. */

	/* now request access to locality. */
	tpm_write_word(TIS_ACCESS_REQUEST_USE, &lpc_tpm_dev[locality].access);

	/* did we get a lock? */
	if (tis_wait_reg(&lpc_tpm_dev[locality].access,
	TIS_ACCESS_ACTIVE_LOCALITY,
	TIS_ACCESS_ACTIVE_LOCALITY) == TPM_TIMEOUT_ERR) {
	printf("%s:%d - failed to lock locality %d\n",
	__FILE__, __LINE__, locality);
	return TPM_DRIVER_ERR;
	}

	tpm_write_word(TIS_STS_COMMAND_READY,
	&lpc_tpm_dev[locality].tpm_status);
	return 0;
	}

	int tis_close(void)
	{
	u8 locality = 0;

	if (tpm_read_word(&lpc_tpm_dev[locality].access) &
	TIS_ACCESS_ACTIVE_LOCALITY) {
	tpm_write_word(TIS_ACCESS_ACTIVE_LOCALITY,
	&lpc_tpm_dev[locality].access);

	if (tis_wait_reg(&lpc_tpm_dev[locality].access,
	TIS_ACCESS_ACTIVE_LOCALITY, 0) ==
	TPM_TIMEOUT_ERR) {
	printf("%s:%d - failed to release locality %d\n",
	__FILE__, __LINE__, locality);
	return TPM_DRIVER_ERR;
	}
	}
	return 0;
	}

	int tis_sendrecv(const u8 *sendbuf, size_t send_size,
	u8 recvbuf, size_t recv_len)
	{
	if (tis_senddata(sendbuf, send_size)) {
	printf("%s:%d failed sending data to TPM\n",
	__FILE__, __LINE__);
	return TPM_DRIVER_ERR;
	}

	return tis_readresponse(recvbuf, (u32 *)recv_len);
	}