Message-Id: <20240105-w1-uart-v3-0-8687093b2e76@gmail.com>
Date: Fri, 05 Jan 2024 09:26:41 +0100
From: Christoph Winklhofer via B4 Relay
 <devnull+cj.winklhofer.gmail.com@...nel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, 
 Rob Herring <robh+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
 Christoph Winklhofer <cj.winklhofer@...il.com>, 
 Rob Herring <robh@...nel.org>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Jiri Slaby <jirislaby@...nel.org>, 
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
 Jonathan Corbet <corbet@....net>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-serial@...r.kernel.org, linux-doc@...r.kernel.org
Subject: [PATCH v3 0/3] w1: add UART w1 bus driver

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 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

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)

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: w1: UART 1-Wire bus
  dt-bindings: serial: allow onewire as child node
  w1: add UART w1 bus driver

 .../devicetree/bindings/serial/serial.yaml    |   2 +-
 .../devicetree/bindings/w1/w1-uart.yaml       |  44 +++
 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 ++++++++++++++++++
 7 files changed, 417 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/devicetree/bindings/w1/w1-uart.yaml
 create mode 100644 Documentation/w1/masters/w1-uart.rst
 create mode 100644 drivers/w1/masters/w1-uart.c

--
2.43.0

base-commit: efc19c44aa442197ddcbb157c6ca54a56eba8c4e
---
Christoph Winklhofer (3):
      dt-bindings: w1: UART 1-Wire bus
      dt-bindings: serial: allow onewire as child node
      w1: add UART w1 bus driver

 .../devicetree/bindings/serial/serial.yaml         |   2 +-
 Documentation/devicetree/bindings/w1/w1-uart.yaml  |  44 +++
 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                       | 350 +++++++++++++++++++++
 7 files changed, 461 insertions(+), 1 deletion(-)
---
base-commit: efc19c44aa442197ddcbb157c6ca54a56eba8c4e
change-id: 20240104-w1-uart-ee8685a15a50

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

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