* [PATCH v2 3/3] w1: add UART w1 bus driver
2023-12-23 10:04 [PATCH v2 0/3] w1: add UART w1 bus driver Christoph Winklhofer
2023-12-23 10:04 ` [PATCH v2 1/3] dt-bindings: w1: UART 1-Wire bus Christoph Winklhofer
2023-12-23 10:04 ` [PATCH v2 2/3] dt-bindings: serial: allow onewire as child node Christoph Winklhofer
@ 2023-12-23 10:04 ` Christoph Winklhofer
2 siblings, 0 replies; 4+ messages in thread
From: Christoph Winklhofer @ 2023-12-23 10:04 UTC (permalink / raw)
To: krzysztof.kozlowski, robh+dt, conor+dt, devicetree, linux-kernel
Cc: Christoph Winklhofer
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@gmail.com>
---
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@gmail.com>
+
+
+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@gmail.com>
+ */
+
+#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@gmail.com>");
+MODULE_LICENSE("GPL");
--
2.43.0
^ permalink raw reply [flat|nested] 4+ messages in thread