[v4,0/3] 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 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: 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  |  62 ++++
 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                       | 398 +++++++++++++++++++++
 7 files changed, 527 insertions(+), 1 deletion(-)
---
base-commit: efc19c44aa442197ddcbb157c6ca54a56eba8c4e
change-id: 20240104-w1-uart-ee8685a15a50

Best regards,
  

On 06/01/2024 17:02, Christoph Winklhofer via B4 Relay wrote:
> 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 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
> 

You can slow down a bit. You sent v2 too late to be applied. Then you
sent v3 and next day v4.

While I like approach to release early, release often, it does not
necessarily apply to the bindings. Bindings should be complete, which
means they should describe the hardware as fully as possible.

About the driver, you can develop it incrementally, it is a good idea,
however since ~rc6 my w1 tree is closed. It will remain closed till next
rc1 is released (merge window finished). Nothing will get applied during
that time, so if you intend to add new features, better to send v5 after
the merge window (instead v4 now, v5 tomorrow, v6 next week and then v7
after rc1).

Best regards,
Krzysztof
  

On Sat, Jan 06, 2024 at 05:56:34PM +0100, Krzysztof Kozlowski wrote:
> On 06/01/2024 17:02, Christoph Winklhofer via B4 Relay wrote:
> > 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 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
> > 
> 
> You can slow down a bit. You sent v2 too late to be applied. Then you
> sent v3 and next day v4.
> 
> While I like approach to release early, release often, it does not
> necessarily apply to the bindings. Bindings should be complete, which
> means they should describe the hardware as fully as possible.
> 
> About the driver, you can develop it incrementally, it is a good idea,
> however since ~rc6 my w1 tree is closed. It will remain closed till next
> rc1 is released (merge window finished). Nothing will get applied during
> that time, so if you intend to add new features, better to send v5 after
> the merge window (instead v4 now, v5 tomorrow, v6 next week and then v7
> after rc1).
> 
> Best regards,
> Krzysztof
> 

Ok sorry, understood - thank you for the clarification.

Kind regards,
Christoph