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/* Copyright (c) 2013 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.
*/
/* I2C arbitration using a pair of GPIO lines */
#include "chipset.h"
#include "common.h"
#include "gpio.h"
#include "hooks.h"
#include "i2c.h"
#include "timer.h"
#include "util.h"
/* Time between requesting bus and deciding that we have it */
#define BUS_SLEW_DELAY_US 10
/* Time between retrying to see if the AP has released the bus */
#define BUS_WAIT_RETRY_US 3000
/* Time to wait until the bus becomes free */
#define BUS_WAIT_FREE_US (100 * 1000)
/*
* This reflects the desired value of GPIO_EC_CLAIM to ensure that the
* GPIO is driven correctly when re-enabled before AP power on.
*/
static char i2c_claimed_by_ec;
int i2c_claim(int port)
{
timestamp_t start;
if (port != I2C_PORT_MASTER)
return EC_SUCCESS;
/* If AP is off, we have the bus */
if (chipset_in_state(CHIPSET_STATE_ANY_OFF)) {
i2c_claimed_by_ec = 1;
return EC_SUCCESS;
}
/* Start a round of trying to claim the bus */
start = get_time();
do {
timestamp_t start_retry;
int waiting = 0;
/* Indicate that we want to claim the bus */
gpio_set_level(GPIO_EC_CLAIM, 0);
usleep(BUS_SLEW_DELAY_US);
/* Wait for the AP to release it */
start_retry = get_time();
while (time_since32(start_retry) < BUS_WAIT_RETRY_US) {
if (gpio_get_level(GPIO_AP_CLAIM)) {
/* We got it, so return */
i2c_claimed_by_ec = 1;
return EC_SUCCESS;
}
if (!waiting)
waiting = 1;
}
/* It didn't release, so give up, wait, and try again */
gpio_set_level(GPIO_EC_CLAIM, 1);
usleep(BUS_WAIT_RETRY_US);
} while (time_since32(start) < BUS_WAIT_FREE_US);
gpio_set_level(GPIO_EC_CLAIM, 1);
usleep(BUS_SLEW_DELAY_US);
i2c_claimed_by_ec = 0;
panic_puts("Unable to access I2C bus (arbitration timeout)\n");
return EC_ERROR_BUSY;
}
void i2c_release(int port)
{
if (port == I2C_PORT_MASTER) {
/* Release our claim */
gpio_set_level(GPIO_EC_CLAIM, 1);
usleep(BUS_SLEW_DELAY_US);
i2c_claimed_by_ec = 0;
}
}
static void i2c_pre_init_hook(void)
{
gpio_set_flags(GPIO_AP_CLAIM, GPIO_PULL_UP);
gpio_set_level(GPIO_EC_CLAIM, i2c_claimed_by_ec ? 0 : 1);
gpio_set_flags(GPIO_EC_CLAIM, GPIO_OUTPUT);
usleep(BUS_SLEW_DELAY_US);
}
DECLARE_HOOK(HOOK_CHIPSET_PRE_INIT, i2c_pre_init_hook, HOOK_PRIO_DEFAULT);
static void i2c_shutdown_hook(void)
{
gpio_set_flags(GPIO_AP_CLAIM, GPIO_INPUT);
gpio_set_flags(GPIO_EC_CLAIM, GPIO_INPUT);
}
DECLARE_HOOK(HOOK_CHIPSET_SHUTDOWN, i2c_shutdown_hook, HOOK_PRIO_DEFAULT);
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