[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

On 06. 01. 24, 17:02, Christoph Winklhofer via B4 Relay wrote:
> 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.
...
> --- /dev/null
> +++ b/drivers/w1/masters/w1-uart.c
> @@ -0,0 +1,398 @@
> +// 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>
> +
> +#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;
> +	unsigned char tx_byte;

If it is a "byte", it should be u8.

> +};
> +
> +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;
> +	unsigned char rx_byte;

The same here.

> +	int rx_err;
> +
> +	struct mutex mutex;
> +};
> +
> +/*
> + * 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 1000000000 / baud;

NSEC_PER_SEC

> +}
> +
> +static inline unsigned int to_ns(unsigned int us)
> +{
> +	return us * 1000;

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 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 * 8 < low_ns + to_ns(limits->sample_us))

BITS_PER_BYTE

> +		return -EINVAL;
> +
> +	/* delay to complete 1-Wire cycle, include start and stop-bit */
> +	w1cfg->delay_us = 0;
> +	if (bit_ns * 10 < to_ns(limits->cycle_us))

What is this 10? Dub it.

> +		w1cfg->delay_us =
> +			(to_ns(limits->cycle_us) - bit_ns * 10) / 1000;

And this 10?

The end: / NSEC_PER_USEC

> +
> +	/* byte to create 1-Wire pulse */
> +	w1cfg->tx_byte = 0xff << bits_low;
> +
> +	return 0;
> +}
...

> +static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
> +				const struct w1_uart_config *w1cfg,
> +				unsigned char *rx_byte)

u8 *

> +{
...
> +}
> +
> +static int w1_uart_serdev_receive_buf(struct serdev_device *serdev,
> +				      const unsigned char *buf, size_t count)

serdev already uses u8 * here. You are basing on the top of some old tree.

regards,

On Mon, Jan 08, 2024 at 07:18:31AM +0100, Jiri Slaby wrote:
> On 06. 01. 24, 17:02, Christoph Winklhofer via B4 Relay wrote:
> > 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.
> ...
> > --- /dev/null
> > +++ b/drivers/w1/masters/w1-uart.c
> > @@ -0,0 +1,398 @@
> > +// 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>
> > +
> > +#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;
> > +	unsigned char tx_byte;
> 
> If it is a "byte", it should be u8.
> 
will change this and all others to u8.

...
> > +
> > +static inline unsigned int baud_to_bit_ns(unsigned int baud)
> > +{
> > +	return 1000000000 / baud;
> 
> NSEC_PER_SEC
> 
> > +}
> > +
> > +static inline unsigned int to_ns(unsigned int us)
> > +{
> > +	return us * 1000;
> 
> NSEC_PER_USEC
> 
and use the correct constants.

...
> > +}
> > +
> > +/*
> > + * 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)
> > +{
...
> > +	/* 1-Wire response detectable for sent byte */
> > +	if (limits->sample_us > 0 &&
> > +	    bit_ns * 8 < low_ns + to_ns(limits->sample_us))
> 
> BITS_PER_BYTE
> 
ok, change it (it is the time for the UART data-frame).
> > +		return -EINVAL;
> > +
> > +	/* delay to complete 1-Wire cycle, include start and stop-bit */
> > +	w1cfg->delay_us = 0;
> > +	if (bit_ns * 10 < to_ns(limits->cycle_us))
> 
> What is this 10? Dub it.
> 
> > +		w1cfg->delay_us =
> > +			(to_ns(limits->cycle_us) - bit_ns * 10) / 1000;
> 
> And this 10?
> 
> The end: / NSEC_PER_USEC
> 
will be more explicit (it is the time for the UART packet:
BITS_PER_BYTE + 2 (start and stop-bit).

...
> > +static int w1_uart_serdev_receive_buf(struct serdev_device *serdev,
> > +				      const unsigned char *buf, size_t count)
> 
> serdev already uses u8 * here. You are basing on the top of some old tree.
Yes, this patch is based on the w1-next branch of
  git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux-w1.git
was not sure from where to start. I guess that this change is probably in
the w1-tree after the next stable release.
> 
> regards,
> -- 
> js
> suse labs
> 
Thanks Jiri for the review!

Kind regards,
Christoph

On 08/01/2024 19:03, Christoph Winklhofer wrote:
> ...
>>> +static int w1_uart_serdev_receive_buf(struct serdev_device *serdev,
>>> +				      const unsigned char *buf, size_t count)
>>
>> serdev already uses u8 * here. You are basing on the top of some old tree.

Old? Your change came for v6.8 and this was sent when all trees were
based on v6.7-rc1. What newer tree could have this been?

> Yes, this patch is based on the w1-next branch of
>   git://git.kernel.org/pub/scm/linux/kernel/git/krzk/linux-w1.git
> was not sure from where to start. I guess that this change is probably in
> the w1-tree after the next stable release.

That's a timing issue. For that particular case, where this was
targeting next-next cycle, you should have based this on linux-next. In
other cases this would require cross-tree merging due to dependencies
which none of us were aware, so no harm.


Best regards,
Krzysztof