path: root/common/i2c_bitbang.c

/* Copyright 2019 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "console.h"
#include "gpio.h"
#include "i2c_bitbang.h"
#include "task.h"
#include "timer.h"
#include "util.h"

#define CPUTS(str) cputs(CC_I2C, str)

static int started;

/* TODO: respect i2c_port->kbps setting */
static void i2c_delay(void)
{
	udelay(5);
}

/* Number of attempts to unwedge each pin. */
#define UNWEDGE_SCL_ATTEMPTS  10
#define UNWEDGE_SDA_ATTEMPTS  3

static void i2c_bitbang_unwedge(const struct i2c_port_t *i2c_port)
{
	int i, j;

	gpio_set_level(i2c_port->scl, 1);
	/*
	 * If clock is low, wait for a while in case of clock stretched
	 * by a peripheral.
	 */
	if (!gpio_get_level(i2c_port->scl)) {
		for (i = 0;; i++) {
			if (i >= UNWEDGE_SCL_ATTEMPTS) {
				/*
				 * If we get here, a peripheral is holding the
				 * clock low and there is nothing we can do.
				 */
				CPUTS("I2C unwedge failed, SCL is held low\n");
				return;
			}
			i2c_delay();
			if (gpio_get_level(i2c_port->scl))
				break;
		}
	}

	if (gpio_get_level(i2c_port->sda))
		return;

	CPUTS("I2C unwedge called with SDA held low\n");

	/* Keep trying to unwedge the SDA line until we run out of attempts. */
	for (i = 0; i < UNWEDGE_SDA_ATTEMPTS; i++) {
		/* Drive the clock high. */
		gpio_set_level(i2c_port->scl, 0);
		i2c_delay();

		/*
		 * Clock through the problem by clocking out 9 bits. If
		 * peripheral releases the SDA line, then we can stop clocking
		 * bits and send a STOP.
		 */
		for (j = 0; j < 9; j++) {
			if (gpio_get_level(i2c_port->sda))
				break;

			gpio_set_level(i2c_port->scl, 0);
			i2c_delay();
			gpio_set_level(i2c_port->scl, 1);
			i2c_delay();
		}

		/* Take control of SDA line and issue a STOP command. */
		gpio_set_level(i2c_port->sda, 0);
		i2c_delay();
		gpio_set_level(i2c_port->sda, 1);
		i2c_delay();

		/* Check if the bus is unwedged. */
		if (gpio_get_level(i2c_port->sda) &&
				gpio_get_level(i2c_port->scl))
			break;
	}

	if (!gpio_get_level(i2c_port->sda))
		CPUTS("I2C unwedge failed, SDA still low\n");
	if (!gpio_get_level(i2c_port->scl))
		CPUTS("I2C unwedge failed, SCL still low\n");
}

static void i2c_stop_cond(const struct i2c_port_t *i2c_port)
{
	int i;

	if (!started)
		return;

	gpio_set_level(i2c_port->sda, 0);
	i2c_delay();

	gpio_set_level(i2c_port->scl, 1);

	/*
	 * SMBus 3.0, 4.2.5
	 *
	 *  the recommendation is that if SMBDAT is still low tTIMEOUT,MAX after
	 *  SMBCLK has gone high at the end of a transaction the controller
	 *  should hold SMBCLK low for at least tTIMEOUT,MAX in an attempt to
	 *  reset the SMBus interface of all of the devices on the bus.
	 */
	for (i = 0; i < 7000; i++) {
		if (gpio_get_level(i2c_port->scl))
			break;
		i2c_delay();
	}
	i2c_delay();

	/* SCL is high, set SDA from 0 to 1 */
	gpio_set_level(i2c_port->sda, 1);
	i2c_delay();

	started = 0;
}

static int clock_stretching(const struct i2c_port_t *i2c_port)
{
	int i;

	i2c_delay();
	/* 5us * 7000 iterations ~= 35ms */
	for (i = 0; i < 7000; i++) {
		if (gpio_get_level(i2c_port->scl))
			return 0;
		i2c_delay();
	}

	/*
	 * SMBus 3.0, Note 3
	 * Devices participating in a transfer can abort the transfer in
	 * progress and release the bus when any single clock low interval
	 * exceeds the value of tTIMEOUT,MIN(=25ms).
	 * After the controller in a transaction detects this condition, it must
	 * generate a stop condition within or after the current data byte in
	 * the transfer process.
	 */
	i2c_stop_cond(i2c_port);
	CPUTS("clock low timeout\n");

	return EC_ERROR_TIMEOUT;
}

static int i2c_start_cond(const struct i2c_port_t *i2c_port)
{
	int err;

	if (started) {
		gpio_set_level(i2c_port->sda, 1);
		i2c_delay();

		gpio_set_level(i2c_port->scl, 1);
		err = clock_stretching(i2c_port);
		if (err)
			return err;
		i2c_delay();

		if (gpio_get_level(i2c_port->sda) == 0) {
			CPUTS("start_cond: arbitration lost\n");
			started = 0;
			return EC_ERROR_UNKNOWN;
		}
	}

	/* check if bus is idle before starting */
	if (gpio_get_level(i2c_port->scl) == 0 ||
	    gpio_get_level(i2c_port->sda) == 0)
		return EC_ERROR_UNKNOWN;

	gpio_set_level(i2c_port->sda, 0);
	i2c_delay();

	gpio_set_level(i2c_port->scl, 0);
	started = 1;

	return 0;
}

static int i2c_write_bit(const struct i2c_port_t *i2c_port, int bit)
{
	int err;

	gpio_set_level(i2c_port->sda, !!bit);
	i2c_delay();

	gpio_set_level(i2c_port->scl, 1);
	err = clock_stretching(i2c_port);
	if (err)
		return err;
	i2c_delay();

	if (bit && gpio_get_level(i2c_port->sda) == 0) {
		CPUTS("write_bit: arbitration lost\n");
		started = 0;
		return EC_ERROR_UNKNOWN;
	}

	gpio_set_level(i2c_port->scl, 0);

	return 0;
}

static int i2c_read_bit(const struct i2c_port_t *i2c_port, int *bit)
{
	int err;

	gpio_set_level(i2c_port->sda, 1);
	i2c_delay();

	gpio_set_level(i2c_port->scl, 1);
	err = clock_stretching(i2c_port);
	if (err)
		return err;
	i2c_delay();
	*bit = gpio_get_level(i2c_port->sda);

	gpio_set_level(i2c_port->scl, 0);

	return 0;
}

static int i2c_write_byte(const struct i2c_port_t *i2c_port, uint8_t byte)
{
	int i, nack, err;

	for (i = 7; i >= 0; i--) {
		err = i2c_write_bit(i2c_port, byte & (1 << i));
		if (err)
			return err;
	}

	err = i2c_read_bit(i2c_port, &nack);
	if (err)
		return err;

	if (nack) {
		/*
		 * The peripheral device detects an invalid command or invalid
		 * data. In this case the peripheral device must NACK the
		 * received byte. The controller upon detection of this
		 * condition must generate a STOP condition and retry the
		 * transaction
		 */
		i2c_stop_cond(i2c_port);
		/* return EC_ERROR_BUSY to indicate i2c_xfer() to retry */
		return EC_ERROR_BUSY;
	}
	return 0;
}

static int i2c_read_byte(const struct i2c_port_t *i2c_port, uint8_t *byte,
		int nack)
{
	int i;

	*byte = 0;
	for (i = 0; i < 8; i++) {
		int bit = 0, err;

		err = i2c_read_bit(i2c_port, &bit);
		if (err)
			return err;
		*byte = (*byte << 1) | bit;
	}

	return i2c_write_bit(i2c_port, nack);
}

static int i2c_bitbang_xfer(const struct i2c_port_t *i2c_port,
		const uint16_t addr_flags,
		const uint8_t *out, int out_size,
		uint8_t *in, int in_size, int flags)
{
	uint16_t addr_8bit = addr_flags << 1, err = EC_SUCCESS;
	int i = 0;

	if (i2c_port->kbps != 100)
		CPUTS("warning: bitbang driver only supports 100kbps\n");

	if (out_size) {
		if (flags & I2C_XFER_START) {
			err = i2c_start_cond(i2c_port);
			if (err)
				goto exit;
			err = i2c_write_byte(i2c_port, addr_8bit);
			if (err)
				goto exit;
		}

		for (i = 0; i < out_size; i++) {
			err = i2c_write_byte(i2c_port, out[i]);
			if (err)
				goto exit;
		}
	}

	if (in_size) {
		if (flags & I2C_XFER_START) {
			err = i2c_start_cond(i2c_port);
			if (err)
				goto exit;
			err = i2c_write_byte(i2c_port, addr_8bit | 1);
			if (err)
				goto exit;
		}

		for (i = 0; i < in_size; i++) {
			err = i2c_read_byte(i2c_port, &in[i],
				(flags & I2C_XFER_STOP) && (i == in_size - 1));
			if (err)
				goto exit;
		}
	}

	if (flags & I2C_XFER_STOP)
		i2c_stop_cond(i2c_port);

exit:
	if (err) {
		i2c_bitbang_unwedge(i2c_port);
		started = 0;
	}
	return err;
}

const struct i2c_drv bitbang_drv = {
	.xfer = &i2c_bitbang_xfer
};

#ifdef TEST_BUILD
int bitbang_start_cond(const struct i2c_port_t *i2c_port)
{
	return i2c_start_cond(i2c_port);
}

void bitbang_stop_cond(const struct i2c_port_t *i2c_port)
{
	i2c_stop_cond(i2c_port);
}

int bitbang_write_byte(const struct i2c_port_t *i2c_port, uint8_t byte)
{
	return i2c_write_byte(i2c_port, byte);
}

void bitbang_set_started(int val)
{
	started = val;
}
#endif