Add a UART 1-Wire bus driver. The driver utilizes the UART interface via the Serial Device Bus to create the 1-Wire timing patterns. The driver was tested on a "Raspberry Pi 3B" with a DS18B20 and on a "Variscite DART-6UL" with a DS18S20 temperature sensor. The 1-Wire timing pattern and the corresponding UART baud-rate with the interpretation of the transferred bytes are described in the document: Link: https://www.analog.com/en/technical-articles/using-a-uart-to-implement-a-1wire-bus-master.html In short, the UART peripheral must support full-duplex and operate in open-drain mode. The timing patterns are generated by a specific combination of baud-rate and transmitted byte, which corresponds to a 1-Wire read bit, write bit or reset. Signed-off-by: Christoph Winklhofer <cj.winklhofer@xxxxxxxxx> --- Documentation/w1/masters/index.rst | 1 + Documentation/w1/masters/w1-uart.rst | 53 +++++ drivers/w1/masters/Kconfig | 10 + drivers/w1/masters/Makefile | 1 + drivers/w1/masters/w1-uart.c | 307 +++++++++++++++++++++++++++ 5 files changed, 372 insertions(+) create mode 100644 Documentation/w1/masters/w1-uart.rst create mode 100644 drivers/w1/masters/w1-uart.c diff --git a/Documentation/w1/masters/index.rst b/Documentation/w1/masters/index.rst index 4442a98850ad..cc40189909fd 100644 --- a/Documentation/w1/masters/index.rst +++ b/Documentation/w1/masters/index.rst @@ -12,3 +12,4 @@ mxc-w1 omap-hdq w1-gpio + w1-uart diff --git a/Documentation/w1/masters/w1-uart.rst b/Documentation/w1/masters/w1-uart.rst new file mode 100644 index 000000000000..2d9d5ec93ddd --- /dev/null +++ b/Documentation/w1/masters/w1-uart.rst @@ -0,0 +1,53 @@ +.. SPDX-License-Identifier: GPL-2.0-or-later + +===================== +Kernel driver w1-uart +===================== + +Author: Christoph Winklhofer <cj.winklhofer@xxxxxxxxx> + + +Description +----------- + +UART 1-Wire bus driver. The driver utilizes the UART interface via the +Serial Device Bus to create the 1-Wire timing patterns as described in +the document `"Using a UART to Implement a 1-Wire Bus Master"`_. + +.. _"Using a UART to Implement a 1-Wire Bus Master": https://www.analog.com/en/technical-articles/using-a-uart-to-implement-a-1wire-bus-master.html + +In short, the UART peripheral must support full-duplex and operate in +open-drain mode. The timing patterns are generated by a specific +combination of baud-rate and transmitted byte, which corresponds to a +1-Wire read bit, write bit or reset pulse. + +For instance the timing pattern for a 1-Wire reset and presence detect uses +the baud-rate 9600, i.e. 104.2 us per bit. The transmitted byte 0xf0 over +UART (least significant bit first, start-bit low) sets the reset low time +for 1-Wire to 521 us. A present 1-Wire device changes the received byte by +pulling the line low, which is used by the driver to evaluate the result of +the 1-Wire operation. + +Similar for a 1-Wire read bit or write bit, which uses the baud-rate +115200, i.e. 8.7 us per bit. The transmitted byte 0x00 is used for a +Write-0 operation and the byte 0xff for Read-0, Read-1 and Write-1. + +The default baud-rate for reset and presence detection is 9600 and for +a 1-Wire read or write operation 115200. In case the actual baud-rate +is different from the requested one, the transmitted byte is adapted +to generate the 1-Wire timing patterns. + + +Usage +----- + +Specify the UART 1-wire bus in the device tree by adding the single child +onewire to the serial node (e.g. uart0). For example: +:: + + @uart0 { + ... + onewire { + compatible = "w1-uart"; + }; + }; diff --git a/drivers/w1/masters/Kconfig b/drivers/w1/masters/Kconfig index 513c0b114337..e6049a75b35b 100644 --- a/drivers/w1/masters/Kconfig +++ b/drivers/w1/masters/Kconfig @@ -78,5 +78,15 @@ config W1_MASTER_SGI This support is also available as a module. If so, the module will be called sgi_w1. +config W1_MASTER_UART + tristate "UART 1-wire driver" + depends on SERIAL_DEV_BUS + help + Say Y here if you want to communicate with your 1-wire devices using + UART interface. + + This support is also available as a module. If so, the module + will be called w1-uart. + endmenu diff --git a/drivers/w1/masters/Makefile b/drivers/w1/masters/Makefile index 6c5a21f9b88c..227f80987e69 100644 --- a/drivers/w1/masters/Makefile +++ b/drivers/w1/masters/Makefile @@ -12,3 +12,4 @@ obj-$(CONFIG_W1_MASTER_MXC) += mxc_w1.o obj-$(CONFIG_W1_MASTER_GPIO) += w1-gpio.o obj-$(CONFIG_HDQ_MASTER_OMAP) += omap_hdq.o obj-$(CONFIG_W1_MASTER_SGI) += sgi_w1.o +obj-$(CONFIG_W1_MASTER_UART) += w1-uart.o diff --git a/drivers/w1/masters/w1-uart.c b/drivers/w1/masters/w1-uart.c new file mode 100644 index 000000000000..6303c8a2a53a --- /dev/null +++ b/drivers/w1/masters/w1-uart.c @@ -0,0 +1,307 @@ +// 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@xxxxxxxxx> + */ + +#include <linux/atomic.h> +#include <linux/completion.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> + +#define W1_UART_TIMEOUT msecs_to_jiffies(500) + +#define baud_to_bit_us(baud) (1000000 / baud) + +struct w1_uart_device { + struct serdev_device *serdev; + struct w1_bus_master bus; + + unsigned int baud_reset; + unsigned char tx_reset; + + unsigned int baud_touch; + unsigned char tx_touch; + + struct completion rx_byte_received; + unsigned char rx_byte; + int rx_err; + + struct mutex mutex; +}; + +/* + * Set baud-rate and tx-byte for 1-Wire reset and presence detect and + * adapt the tx-byte according to the actual baud-rate. + * + * Minimum reset low time is 480us and the response from a 1-Wire + * device is at around 570us. Reject when a bit takes longer than + * 500us or is to short to detect a manipulated byte. + * + */ +static int w1_uart_set_baud_reset(struct w1_uart_device *w1dev) +{ + struct serdev_device *serdev = w1dev->serdev; + unsigned int bit_us; + unsigned int bits_low; + + w1dev->baud_reset = serdev_device_set_baudrate(serdev, 9600); + if (w1dev->baud_reset == 0) + return -EINVAL; + + bit_us = baud_to_bit_us(w1dev->baud_reset); + + /* reset low time is 480us */ + if (bit_us > 500) + return -EINVAL; + + /* At least Bit-8 should be manipulated by a present device, + * which is at 570us. Bit-8 and start-bit: 9 * 65us + */ + if (bit_us < 65) + return -EINVAL; + + /* byte to create reset pulse (start-bit is low) */ + bits_low = 500 / bit_us; + w1dev->tx_reset = 0xff << bits_low; + + return 0; +} + +/* + * Set baud-rate and tx-byte for 1-Wire read and write cycle and + * adapt the tx-byte according to the actual baud-rate. + * + * Recommended low-time to initiate a Write-1 or Read is 6us. Time-slot + * for 1-Wire bit operation is 70us. Reject when a bit takes longer + * than 10us (recommended 6us) or the entire time-slot is to short. + */ +static int w1_uart_set_baud_touch(struct w1_uart_device *w1dev) +{ + struct serdev_device *serdev = w1dev->serdev; + unsigned int bits_low; + unsigned int bit_us; + + w1dev->baud_touch = serdev_device_set_baudrate(serdev, 115200); + if (w1dev->baud_touch == 0) + return -EINVAL; + + bit_us = baud_to_bit_us(w1dev->baud_touch); + /* low-time to start write-1 and read cycle */ + if (bit_us > 10) + return -EINVAL; + /* 1-Wire time slot is 70 us */ + if (bit_us < 7) + return -EINVAL; + + /* max low time 10us */ + bits_low = 5 / bit_us; + w1dev->tx_touch = 0xff << bits_low; + + return 0; +} + +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_baud_reset(w1dev); + if (ret < 0) { + dev_err(dev, "set baud-rate for reset failed\n"); + return ret; + } + + ret = w1_uart_set_baud_touch(w1dev); + if (ret < 0) { + dev_err(dev, "set baud-rate for touch 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, + unsigned int baudrate, unsigned char tx_byte, + unsigned char *rx_byte) +{ + struct serdev_device *serdev = w1dev->serdev; + int ret; + + serdev_device_write_flush(serdev); + serdev_device_set_baudrate(serdev, baudrate); + + /* write and immediately read one byte */ + reinit_completion(&w1dev->rx_byte_received); + ret = serdev_device_write_buf(serdev, &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 during driver remove or when serdev + * is unexpectedly in the receive callback. + */ + if (!mutex_trylock(&w1dev->mutex)) + return -EIO; + + ret = w1dev->rx_err; + if (ret == 0) + *rx_byte = w1dev->rx_byte; + + mutex_unlock(&w1dev->mutex); + + return ret; +} + +static int w1_uart_serdev_receive_buf(struct serdev_device *serdev, + const unsigned char *buf, size_t count) +{ + struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev); + + mutex_lock(&w1dev->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->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; + unsigned char val; + int ret; + + ret = w1_uart_serdev_tx_rx(w1dev, w1dev->baud_reset, w1dev->tx_reset, + &val); + if (ret < 0) + return -1; + + /* Device present (0) or no device (1) */ + return val != w1dev->tx_reset ? 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; + unsigned char val; + int ret; + + ret = w1_uart_serdev_tx_rx(w1dev, w1dev->baud_touch, + bit ? w1dev->tx_touch : 0x00, &val); + /* return inactive bus state on error */ + if (ret < 0) + return 1; + + return val == w1dev->tx_touch ? 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->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); + + mutex_lock(&w1dev->mutex); + + w1_remove_master_device(&w1dev->bus); + + mutex_unlock(&w1dev->mutex); +} + +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@xxxxxxxxx>"); +MODULE_LICENSE("GPL"); -- 2.43.0
