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/* 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 CPRINTS(format, args...) cprints(CC_I2C, format, ## args)
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.
*/
CPRINTS("I2C%d unwedge failed, "
"SCL is held low", i2c_port->port);
return;
}
i2c_delay();
if (gpio_get_level(i2c_port->scl))
break;
}
}
if (gpio_get_level(i2c_port->sda))
return;
CPRINTS("I2C%d unwedge called with SDA held low", i2c_port->port);
/* 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))
CPRINTS("I2C%d unwedge failed, SDA still low", i2c_port->port);
if (!gpio_get_level(i2c_port->scl))
CPRINTS("I2C%d unwedge failed, SCL still low", i2c_port->port);
}
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);
CPRINTS("clock low timeout");
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) {
CPRINTS("%s: arbitration lost", __func__);
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) {
CPRINTS("%s: arbitration lost", __func__);
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)
CPRINTS("warning: bitbang driver only supports 100kbps");
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
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