Message-ID: <5ff1d706-9f06-4eb6-bc86-75f933e54118@kernel.org>
Date: Mon, 8 Jan 2024 07:18:31 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: cj.winklhofer@...il.com,
 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Rob Herring <robh+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Rob Herring <robh@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.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: Re: [PATCH v4 3/3] w1: add UART w1 bus driver

On 06. 01. 24, 17:02, Christoph Winklhofer via B4 Relay wrote:
> From: Christoph Winklhofer <cj.winklhofer@...il.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@...il.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,
-- 
js
suse labs

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