--- /dev/null
+// 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 <cj.winklhofer@gmail.com>
+ */
+
+#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 <cj.winklhofer@gmail.com>");
+MODULE_LICENSE("GPL");
projects / linux.git / commitdiff