// SPDX-License-Identifier: GPL-2.0-or-later
/*
* w1-uart - UART 1-Wire bus driver
*
* Uses the UART interface (via Serial Device Bus) to create the 1-Wire
* timing patterns. Implements the following 1-Wire master interface:
*
* - reset_bus: requests baud-rate 9600
*
* - touch_bit: requests baud-rate 115200
*
* Author: Christoph Winklhofer <[email protected]>
*/
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/serdev.h>
#include <linux/w1.h>
/* UART packet contains start and stop bit */
#define W1_UART_BITS_PER_PACKET (BITS_PER_BYTE + 2)
/* Timeout to wait for completion of serdev-receive */
#define W1_UART_TIMEOUT msecs_to_jiffies(500)
/**
* struct w1_uart_config - configuration for 1-Wire operation
* @baudrate: baud-rate returned from serdev
* @delay_us: delay to complete a 1-Wire cycle (in us)
* @tx_byte: byte to generate 1-Wire timing pattern
*/
struct w1_uart_config {
unsigned int baudrate;
unsigned int delay_us;
u8 tx_byte;
};
/**
* struct w1_uart_device - 1-Wire UART device structure
* @serdev: serial device
* @bus: w1-bus master
* @cfg_reset: config for 1-Wire reset
* @cfg_touch_0: config for 1-Wire write-0 cycle
* @cfg_touch_1: config for 1-Wire write-1 and read cycle
* @rx_byte_received: completion for serdev receive
* @rx_mutex: mutex to protect rx_err and rx_byte
* @rx_err: indicates an error in serdev-receive
* @rx_byte: result byte from serdev-receive
*/
struct w1_uart_device {
struct serdev_device *serdev;
struct w1_bus_master bus;
struct w1_uart_config cfg_reset;
struct w1_uart_config cfg_touch_0;
struct w1_uart_config cfg_touch_1;
struct completion rx_byte_received;
/*
* protect rx_err and rx_byte from concurrent access in
* w1-callbacks and serdev-receive.
*/
struct mutex rx_mutex;
int rx_err;
u8 rx_byte;
};
/**
* struct w1_uart_limits - limits for 1-Wire operations
* @baudrate: Requested baud-rate to create 1-Wire timing pattern
* @bit_min_us: minimum time for a bit (in us)
* @bit_max_us: maximum time for a bit (in us)
* @sample_us: timespan to sample 1-Wire response
* @cycle_us: duration of the 1-Wire cycle
*/
struct w1_uart_limits {
unsigned int baudrate;
unsigned int bit_min_us;
unsigned int bit_max_us;
unsigned int sample_us;
unsigned int cycle_us;
};
static inline unsigned int baud_to_bit_ns(unsigned int baud)
{
return NSEC_PER_SEC / baud;
}
static inline unsigned int to_ns(unsigned int us)
{
return us * NSEC_PER_USEC;
}
/*
* Set baud-rate, delay and tx-byte to create a 1-Wire pulse and adapt
* the tx-byte according to the actual baud-rate.
*
* Reject when:
* - time for a bit outside min/max range
* - a 1-Wire response is not detectable for sent byte
*/
static int w1_uart_set_config(struct serdev_device *serdev,
const struct w1_uart_limits *limits,
struct w1_uart_config *w1cfg)
{
unsigned int packet_ns;
unsigned int bits_low;
unsigned int bit_ns;
unsigned int low_ns;
w1cfg->baudrate = serdev_device_set_baudrate(serdev, limits->baudrate);
if (w1cfg->baudrate == 0)
return -EINVAL;
/* Compute in nanoseconds for accuracy */
bit_ns = baud_to_bit_ns(w1cfg->baudrate);
bits_low = to_ns(limits->bit_min_us) / bit_ns;
/* start bit is always low */
low_ns = bit_ns * (bits_low + 1);
if (low_ns < to_ns(limits->bit_min_us))
return -EINVAL;
if (low_ns > to_ns(limits->bit_max_us))
return -EINVAL;
/* 1-Wire response detectable for sent byte */
if (limits->sample_us > 0 &&
bit_ns * BITS_PER_BYTE < low_ns + to_ns(limits->sample_us))
return -EINVAL;
/* delay: 1-Wire cycle takes longer than the UART packet */
packet_ns = bit_ns * W1_UART_BITS_PER_PACKET;
w1cfg->delay_us = 0;
if (to_ns(limits->cycle_us) > packet_ns)
w1cfg->delay_us =
(to_ns(limits->cycle_us) - packet_ns) / NSEC_PER_USEC;
/* byte to create 1-Wire pulse */
w1cfg->tx_byte = 0xff << bits_low;
return 0;
}
/*
* Configuration for reset and presence detect
* - bit_min_us is 480us, add margin and use 485us
* - limits for sample time 60us-75us, use 65us
*/
static int w1_uart_set_config_reset(struct w1_uart_device *w1dev)
{
struct serdev_device *serdev = w1dev->serdev;
struct device_node *np = serdev->dev.of_node;
struct w1_uart_limits limits = { .baudrate = 9600,
.bit_min_us = 485,
.bit_max_us = 640,
.sample_us = 65,
.cycle_us = 960 };
of_property_read_u32(np, "reset-bps", &limits.baudrate);
return w1_uart_set_config(serdev, &limits, &w1dev->cfg_reset);
}
/*
* Configuration for write-0 cycle (touch bit 0)
* - bit_min_us is 60us, add margin and use 65us
* - no sampling required, sample_us = 0
*/
static int w1_uart_set_config_touch_0(struct w1_uart_device *w1dev)
{
struct serdev_device *serdev = w1dev->serdev;
struct device_node *np = serdev->dev.of_node;
struct w1_uart_limits limits = { .baudrate = 115200,
.bit_min_us = 65,
.bit_max_us = 120,
.sample_us = 0,
.cycle_us = 70 };
of_property_read_u32(np, "write-0-bps", &limits.baudrate);
return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_0);
}
/*
* Configuration for write-1 and read cycle (touch bit 1)
* - bit_min_us is 5us, add margin and use 6us
* - limits for sample time 5us-15us, use 15us
*/
static int w1_uart_set_config_touch_1(struct w1_uart_device *w1dev)
{
struct serdev_device *serdev = w1dev->serdev;
struct device_node *np = serdev->dev.of_node;
struct w1_uart_limits limits = { .baudrate = 115200,
.bit_min_us = 6,
.bit_max_us = 15,
.sample_us = 15,
.cycle_us = 70 };
of_property_read_u32(np, "write-1-bps", &limits.baudrate);
return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_1);
}
/*
* Configure and open the serial device
*/
static int w1_uart_serdev_open(struct w1_uart_device *w1dev)
{
struct serdev_device *serdev = w1dev->serdev;
struct device *dev = &serdev->dev;
int ret;
ret = devm_serdev_device_open(dev, serdev);
if (ret < 0)
return ret;
ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
if (ret < 0) {
dev_err(dev, "set parity failed\n");
return ret;
}
ret = w1_uart_set_config_reset(w1dev);
if (ret < 0) {
dev_err(dev, "config for reset failed\n");
return ret;
}
ret = w1_uart_set_config_touch_0(w1dev);
if (ret < 0) {
dev_err(dev, "config for touch-0 failed\n");
return ret;
}
ret = w1_uart_set_config_touch_1(w1dev);
if (ret < 0) {
dev_err(dev, "config for touch-1 failed\n");
return ret;
}
serdev_device_set_flow_control(serdev, false);
return 0;
}
/*
* Send one byte (tx_byte) and read one byte (rx_byte) via serdev.
*/
static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
const struct w1_uart_config *w1cfg, u8 *rx_byte)
{
struct serdev_device *serdev = w1dev->serdev;
int ret;
serdev_device_write_flush(serdev);
serdev_device_set_baudrate(serdev, w1cfg->baudrate);
/* write and immediately read one byte */
reinit_completion(&w1dev->rx_byte_received);
ret = serdev_device_write_buf(serdev, &w1cfg->tx_byte, 1);
if (ret != 1)
return -EIO;
ret = wait_for_completion_interruptible_timeout(
&w1dev->rx_byte_received, W1_UART_TIMEOUT);
if (ret <= 0)
return -EIO;
/* locking could fail when serdev is unexpectedly receiving. */
if (!mutex_trylock(&w1dev->rx_mutex))
return -EIO;
ret = w1dev->rx_err;
if (ret == 0)
*rx_byte = w1dev->rx_byte;
mutex_unlock(&w1dev->rx_mutex);
if (w1cfg->delay_us > 0)
fsleep(w1cfg->delay_us);
return ret;
}
static size_t w1_uart_serdev_receive_buf(struct serdev_device *serdev,
const u8 *buf, size_t count)
{
struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
mutex_lock(&w1dev->rx_mutex);
/* sent a single byte and receive one single byte */
if (count == 1) {
w1dev->rx_byte = buf[0];
w1dev->rx_err = 0;
} else {
w1dev->rx_err = -EIO;
}
mutex_unlock(&w1dev->rx_mutex);
complete(&w1dev->rx_byte_received);
return count;
}
static const struct serdev_device_ops w1_uart_serdev_ops = {
.receive_buf = w1_uart_serdev_receive_buf,
.write_wakeup = serdev_device_write_wakeup,
};
/*
* 1-wire reset and presence detect: A present slave will manipulate
* the received byte by pulling the 1-Wire low.
*/
static u8 w1_uart_reset_bus(void *data)
{
struct w1_uart_device *w1dev = data;
const struct w1_uart_config *w1cfg = &w1dev->cfg_reset;
int ret;
u8 val;
ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
if (ret < 0)
return -1;
/* Device present (0) or no device (1) */
return val != w1cfg->tx_byte ? 0 : 1;
}
/*
* 1-Wire read and write cycle: Only the read-0 manipulates the
* received byte, all others left the line untouched.
*/
static u8 w1_uart_touch_bit(void *data, u8 bit)
{
struct w1_uart_device *w1dev = data;
const struct w1_uart_config *w1cfg = bit ? &w1dev->cfg_touch_1 :
&w1dev->cfg_touch_0;
int ret;
u8 val;
ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
/* return inactive bus state on error */
if (ret < 0)
return 1;
return val == w1cfg->tx_byte ? 1 : 0;
}
static int w1_uart_probe(struct serdev_device *serdev)
{
struct device *dev = &serdev->dev;
struct w1_uart_device *w1dev;
int ret;
w1dev = devm_kzalloc(dev, sizeof(*w1dev), GFP_KERNEL);
if (!w1dev)
return -ENOMEM;
w1dev->bus.data = w1dev;
w1dev->bus.reset_bus = w1_uart_reset_bus;
w1dev->bus.touch_bit = w1_uart_touch_bit;
w1dev->serdev = serdev;
init_completion(&w1dev->rx_byte_received);
mutex_init(&w1dev->rx_mutex);
ret = w1_uart_serdev_open(w1dev);
if (ret < 0)
return ret;
serdev_device_set_drvdata(serdev, w1dev);
serdev_device_set_client_ops(serdev, &w1_uart_serdev_ops);
return w1_add_master_device(&w1dev->bus);
}
static void w1_uart_remove(struct serdev_device *serdev)
{
struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
/*
* Waits until w1-uart callbacks are finished, serdev is closed
* and its device data released automatically by devres (waits
* until serdev-receive is finished).
*/
w1_remove_master_device(&w1dev->bus);
}
static const struct of_device_id w1_uart_of_match[] = {
{ .compatible = "w1-uart" },
{},
};
MODULE_DEVICE_TABLE(of, w1_uart_of_match);
static struct serdev_device_driver w1_uart_driver = {
.driver = {
.name = "w1-uart",
.of_match_table = w1_uart_of_match,
},
.probe = w1_uart_probe,
.remove = w1_uart_remove,
};
module_serdev_device_driver(w1_uart_driver);
MODULE_DESCRIPTION("UART w1 bus driver");
MODULE_AUTHOR("Christoph Winklhofer <[email protected]>");
MODULE_LICENSE("GPL");
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