linux-kernel - [PATCH 0/2] w1: add UART w1 bus driver

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Message-ID: <20231217122004.42795-1-cj.winklhofer@gmail.com>
Date: Sun, 17 Dec 2023 13:20:02 +0100
From: Christoph Winklhofer <cj.winklhofer@...il.com>
To: krzysztof.kozlowski@...aro.org,
	robh+dt@...nel.org,
	conor+dt@...nel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Christoph Winklhofer <cj.winklhofer@...il.com>
Subject: [PATCH 0/2] w1: add UART w1 bus driver

Hello!

This patch set 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.

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
- Patch 2: 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 (2):
  dt-bindings: w1: UART 1-wire bus
  w1: add UART w1 bus driver

 .../devicetree/bindings/w1/w1-uart.yaml       |  27 +++
 Documentation/w1/masters/index.rst            |   1 +
 Documentation/w1/masters/w1-uart.rst          |  48 +++++
 drivers/w1/masters/Kconfig                    |  10 +
 drivers/w1/masters/Makefile                   |   1 +
 drivers/w1/masters/w1-uart.c                  | 189 ++++++++++++++++++
 6 files changed, 276 insertions(+)
 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

base-commit: efc19c44aa442197ddcbb157c6ca54a56eba8c4e
-- 
2.43.0