[PATCH v7 0/3] w1: add UART w1 bus driver

[PATCH v7 0/3] w1: add UART w1 bus driver

[Christoph Winklhofer via B4 Relay]

Hello!

This patch contains a driver for a 1-Wire bus over UART. The driver
utilizes the UART interface via the Serial Device Bus to create the
1-Wire timing patterns.

Changes in v7:
- rename mutex to rx_mutex and comment its usage
- fix comments and use kerneldoc for internal structs
- Link to v6: https://lore.kernel.org/r/20240209-w1-uart-v6-0-3e753c149196@gmail.com
Thanks Krzysztof for the review.

Changes in v6:
- change order of patches for dt-binding
- remove unnecessary lock in remove
- delay for 1-Wire cycle without mutex lock 
- fix comment style and add some more comments
- Link to v5: https://lore.kernel.org/r/20240126-w1-uart-v5-0-1d82bfdc2ae9@gmail.com
Thanks Krzysztof and Rob for the review.

Changes in v5:
- dt-binding: allow child object for onewire and use prefix -bps for
  baud rate configuration.
- use type u8 for a byte, instead of unsigned char
- use constants (NSEC_PER_SEC, BITS_PER_BYTE)
- make delay computation from packet time more coherent
- Link to v4: https://lore.kernel.org/r/20240106-w1-uart-v4-0-7fe1378a8b3e@gmail.com
Thanks Jiri, Krzysztof and Rob for the review.

Changes in v4:
- rework baud-rate configuration: also check max bit-time, support higher
  baud-rates by adding a delay to complete 1-Wire cycle.
- dt-binding w1-uart: specify baud-rates for 1-Wire operations
- Link to v3: https://lore.kernel.org/r/20240105-w1-uart-v3-0-8687093b2e76@gmail.com

Changes in v3:
- improve baud-rate configuration: use specific limits for 1-Wire
  reset, touch-0 and touch-1 operation, compute in nanoseconds.
- remove unused header atomic.h
- use function instead of macro to compute bit-time from baud-rate
- switch to b4 util to publish patch: missing recipients
- Link to v2: https://lore.kernel.org/lkml/20231223100408.44056-1-cj.winklhofer@gmail.com

Changes in v2:
- add documentation for dt-binding
- allow onewire as serial child node
- support different baud-rates: The driver requests a baud-rate (9600
  for reset and 115200 for write/read) and tries to adapt the
  transmitted byte according to the actual baud-rate returned from
  serdev.
- fix locking problem for serdev-receive and w1-master reset/touch: The
  received byte is now protected with a mutex - instead of the atomic,
  which was used before due to the concurrent store and load.
- explicit error in serdev-receive: Receiving more than one byte results
  in an error, since the w1-uart driver is the only writer, it writes a
  single-byte and should receive a single byte.
- fix variable names, errno-returns, wrong define CONFIG_OF
- fix log flooding
- fix driver remove (error-path for rxtx-function)
- Link to v1: https://lore.kernel.org/all/20231217122004.42795-1-cj.winklhofer@gmail.com
Krzysztof, thank your very much for your feedback!

It was tested on a "Raspberry Pi 3 Model B+" with a DS18B20 and on a
"Variscite DART-6UL" with a DS18S20 temperature sensor.

Content:
- Patch 1: device tree binding 1-Wire
- Patch 2: allow onewire as serial child node
- Patch 3: driver and documentation

The patch was created against the w1 subsytem tree (branch w1-next):
  Link: https://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux-w1.git/

The checkpatch.pl script reported the following error - which I am not
sure how to fix:
  WARNING: added, moved or deleted file(s), does MAINTAINERS need
  updating?

The technical details for 1-Wire over UART are 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 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.

Hope the driver is helpful.

Thanks,
Christoph

---
Christoph Winklhofer (3):
      dt-bindings: serial: allow onewire as child node
      dt-bindings: w1: UART 1-Wire bus
      w1: add UART w1 bus driver

 .../devicetree/bindings/serial/serial.yaml         |   2 +-
 Documentation/devicetree/bindings/w1/w1-uart.yaml  |  60 +++
 Documentation/w1/masters/index.rst                 |   1 +
 Documentation/w1/masters/w1-uart.rst               |  54 +++
 drivers/w1/masters/Kconfig                         |  10 +
 drivers/w1/masters/Makefile                        |   1 +
 drivers/w1/masters/w1-uart.c                       | 415 +++++++++++++++++++++
 7 files changed, 542 insertions(+), 1 deletion(-)
---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20240104-w1-uart-ee8685a15a50

Best regards,
-- 
Christoph Winklhofer <cj.winklhofer@gmail.com>

[PATCH v7 1/3] dt-bindings: serial: allow onewire as child node

[Christoph Winklhofer via B4 Relay]

From: Christoph Winklhofer <cj.winklhofer@gmail.com>

The UART 1-Wire bus utilizes the Serial Device Bus to create the 1-wire
timing patterns.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Christoph Winklhofer <cj.winklhofer@gmail.com>
---
 Documentation/devicetree/bindings/serial/serial.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/serial/serial.yaml b/Documentation/devicetree/bindings/serial/serial.yaml
index 65804ca274ae..ffc9198ae214 100644
--- a/Documentation/devicetree/bindings/serial/serial.yaml
+++ b/Documentation/devicetree/bindings/serial/serial.yaml
@@ -88,7 +88,7 @@ properties:
       TX FIFO threshold configuration (in bytes).
 
 patternProperties:
-  "^(bluetooth|bluetooth-gnss|gnss|gps|mcu)$":
+  "^(bluetooth|bluetooth-gnss|gnss|gps|mcu|onewire)$":
     if:
       type: object
     then:

-- 
2.43.0

[PATCH v7 2/3] dt-bindings: w1: UART 1-Wire bus

[Christoph Winklhofer via B4 Relay]

From: Christoph Winklhofer <cj.winklhofer@gmail.com>

Add device tree binding for UART 1-Wire bus.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Christoph Winklhofer <cj.winklhofer@gmail.com>
---
 Documentation/devicetree/bindings/w1/w1-uart.yaml | 60 +++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/Documentation/devicetree/bindings/w1/w1-uart.yaml b/Documentation/devicetree/bindings/w1/w1-uart.yaml
new file mode 100644
index 000000000000..7173820c78f9
--- /dev/null
+++ b/Documentation/devicetree/bindings/w1/w1-uart.yaml
@@ -0,0 +1,60 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/w1/w1-uart.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: UART 1-Wire Bus
+
+maintainers:
+  - Christoph Winklhofer <cj.winklhofer@gmail.com>
+
+description: |
+  UART 1-wire bus. Utilizes the UART interface via the Serial Device Bus
+  to create the 1-Wire timing patterns.
+
+  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.
+
+  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.
+
+  https://www.analog.com/en/technical-articles/using-a-uart-to-implement-a-1wire-bus-master.html
+
+
+properties:
+  compatible:
+    const: w1-uart
+
+  reset-bps:
+    default: 9600
+    description:
+      The baud rate for the 1-Wire reset and presence detect.
+
+  write-0-bps:
+    default: 115200
+    description:
+      The baud rate for the 1-Wire write-0 cycle.
+
+  write-1-bps:
+    default: 115200
+    description:
+      The baud rate for the 1-Wire write-1 and read cycle.
+
+required:
+  - compatible
+
+additionalProperties:
+  type: object
+
+examples:
+  - |
+    serial {
+        onewire {
+            compatible = "w1-uart";
+        };
+    };

-- 
2.43.0

[PATCH v7 3/3] w1: add UART w1 bus driver

[Christoph Winklhofer via B4 Relay]

From: Christoph Winklhofer <cj.winklhofer@gmail.com>

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 |  54 +++++
 drivers/w1/masters/Kconfig           |  10 +
 drivers/w1/masters/Makefile          |   1 +
 drivers/w1/masters/w1-uart.c         | 415 +++++++++++++++++++++++++++++++++++
 5 files changed, 481 insertions(+)

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..8d0f122178d4
--- /dev/null
+++ b/Documentation/w1/masters/w1-uart.rst
@@ -0,0 +1,54 @@
+.. 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 0x80 is used for a
+Write-0 operation (low time 69.6us) and the byte 0xff for Read-0, Read-1
+and Write-1 (low time 8.7us).
+
+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..6950d29d7dac
--- /dev/null
+++ b/drivers/w1/masters/w1-uart.c
@@ -0,0 +1,415 @@
+// 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 ssize_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");

-- 
2.43.0

Re: (subset) [PATCH v7 3/3] w1: add UART w1 bus driver

[Krzysztof Kozlowski]

On Wed, 14 Feb 2024 07:36:15 +0100, Christoph Winklhofer wrote:
> 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:
> 
> [...]

Applied, thanks!

[3/3] w1: add UART w1 bus driver
      https://git.kernel.org/krzk/linux-w1/c/178cf9db9e6d8fb0c026098c8f2d1fd92ae3d79b

Best regards,
-- 
Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Re: [PATCH v7 2/3] dt-bindings: w1: UART 1-Wire bus

[Krzysztof Kozlowski]

On 14/02/2024 07:36, Christoph Winklhofer via B4 Relay wrote:
> From: Christoph Winklhofer <cj.winklhofer@gmail.com>
> 
> Add device tree binding for UART 1-Wire bus.
> 
> Reviewed-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Christoph Winklhofer <cj.winklhofer@gmail.com>
> ---

No need to send applied patches.

Best regards,
Krzysztof