[PATCH v6 0/3] w1: add UART w1 bus driver

[Christoph Winklhofer <cj.winklhofer@gmail.com>]

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 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                       | 417 +++++++++++++++++++++
 7 files changed, 544 insertions(+), 1 deletion(-)
---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20240104-w1-uart-ee8685a15a50

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