w1: add UART w1 bus driver
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. Signed-off-by: Christoph Winklhofer <cj.winklhofer@gmail.com> Link: https://lore.kernel.org/r/20240214-w1-uart-v7-3-6e21fa24e066@gmail.com [krzysztof: w1_uart_serdev_receive_buf() return type fixup] Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
This commit is contained in:
Christoph Winklhofer
Krzysztof Kozlowski
parent
23b3333753
commit
a3c0880436
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@ -12,3 +12,4 @@
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mxc-w1
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omap-hdq
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w1-gpio
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w1-uart
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@ -0,0 +1,54 @@
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.. SPDX-License-Identifier: GPL-2.0-or-later
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=====================
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Kernel driver w1-uart
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=====================
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Author: Christoph Winklhofer <cj.winklhofer@gmail.com>
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Description
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-----------
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UART 1-Wire bus driver. The driver utilizes the UART interface via the
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Serial Device Bus to create the 1-Wire timing patterns as described in
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the document `"Using a UART to Implement a 1-Wire Bus Master"`_.
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.. _"Using a UART to Implement a 1-Wire Bus Master": https://www.analog.com/en/technical-articles/using-a-uart-to-implement-a-1wire-bus-master.html
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In short, the UART peripheral must support full-duplex and operate in
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open-drain mode. The timing patterns are generated by a specific
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combination of baud-rate and transmitted byte, which corresponds to a
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1-Wire read bit, write bit or reset pulse.
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For instance the timing pattern for a 1-Wire reset and presence detect uses
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the baud-rate 9600, i.e. 104.2 us per bit. The transmitted byte 0xf0 over
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UART (least significant bit first, start-bit low) sets the reset low time
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for 1-Wire to 521 us. A present 1-Wire device changes the received byte by
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pulling the line low, which is used by the driver to evaluate the result of
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the 1-Wire operation.
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Similar for a 1-Wire read bit or write bit, which uses the baud-rate
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115200, i.e. 8.7 us per bit. The transmitted byte 0x80 is used for a
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Write-0 operation (low time 69.6us) and the byte 0xff for Read-0, Read-1
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and Write-1 (low time 8.7us).
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The default baud-rate for reset and presence detection is 9600 and for
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a 1-Wire read or write operation 115200. In case the actual baud-rate
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is different from the requested one, the transmitted byte is adapted
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to generate the 1-Wire timing patterns.
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Usage
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-----
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Specify the UART 1-wire bus in the device tree by adding the single child
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onewire to the serial node (e.g. uart0). For example:
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::
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@uart0 {
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...
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onewire {
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compatible = "w1-uart";
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};
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};
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@ -78,5 +78,15 @@ config W1_MASTER_SGI
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This support is also available as a module. If so, the module
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will be called sgi_w1.
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config W1_MASTER_UART
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tristate "UART 1-wire driver"
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depends on SERIAL_DEV_BUS
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help
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Say Y here if you want to communicate with your 1-wire devices using
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UART interface.
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This support is also available as a module. If so, the module
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will be called w1-uart.
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endmenu
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@ -12,3 +12,4 @@ obj-$(CONFIG_W1_MASTER_MXC) += mxc_w1.o
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obj-$(CONFIG_W1_MASTER_GPIO) += w1-gpio.o
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obj-$(CONFIG_HDQ_MASTER_OMAP) += omap_hdq.o
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obj-$(CONFIG_W1_MASTER_SGI) += sgi_w1.o
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obj-$(CONFIG_W1_MASTER_UART) += w1-uart.o
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@ -0,0 +1,415 @@
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// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* w1-uart - UART 1-Wire bus driver
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*
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* Uses the UART interface (via Serial Device Bus) to create the 1-Wire
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* timing patterns. Implements the following 1-Wire master interface:
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*
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* - reset_bus: requests baud-rate 9600
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*
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* - touch_bit: requests baud-rate 115200
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*
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* Author: Christoph Winklhofer <cj.winklhofer@gmail.com>
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*/
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#include <linux/completion.h>
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#include <linux/delay.h>
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#include <linux/jiffies.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/of.h>
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#include <linux/serdev.h>
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#include <linux/w1.h>
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/* UART packet contains start and stop bit */
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#define W1_UART_BITS_PER_PACKET (BITS_PER_BYTE + 2)
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/* Timeout to wait for completion of serdev-receive */
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#define W1_UART_TIMEOUT msecs_to_jiffies(500)
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/**
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* struct w1_uart_config - configuration for 1-Wire operation
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* @baudrate: baud-rate returned from serdev
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* @delay_us: delay to complete a 1-Wire cycle (in us)
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* @tx_byte: byte to generate 1-Wire timing pattern
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*/
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struct w1_uart_config {
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unsigned int baudrate;
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unsigned int delay_us;
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u8 tx_byte;
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};
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/**
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* struct w1_uart_device - 1-Wire UART device structure
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* @serdev: serial device
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* @bus: w1-bus master
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* @cfg_reset: config for 1-Wire reset
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* @cfg_touch_0: config for 1-Wire write-0 cycle
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* @cfg_touch_1: config for 1-Wire write-1 and read cycle
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* @rx_byte_received: completion for serdev receive
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* @rx_mutex: mutex to protect rx_err and rx_byte
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* @rx_err: indicates an error in serdev-receive
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* @rx_byte: result byte from serdev-receive
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*/
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struct w1_uart_device {
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struct serdev_device *serdev;
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struct w1_bus_master bus;
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struct w1_uart_config cfg_reset;
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struct w1_uart_config cfg_touch_0;
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struct w1_uart_config cfg_touch_1;
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struct completion rx_byte_received;
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/*
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* protect rx_err and rx_byte from concurrent access in
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* w1-callbacks and serdev-receive.
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*/
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struct mutex rx_mutex;
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int rx_err;
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u8 rx_byte;
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};
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/**
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* struct w1_uart_limits - limits for 1-Wire operations
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* @baudrate: Requested baud-rate to create 1-Wire timing pattern
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* @bit_min_us: minimum time for a bit (in us)
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* @bit_max_us: maximum time for a bit (in us)
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* @sample_us: timespan to sample 1-Wire response
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* @cycle_us: duration of the 1-Wire cycle
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*/
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struct w1_uart_limits {
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unsigned int baudrate;
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unsigned int bit_min_us;
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unsigned int bit_max_us;
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unsigned int sample_us;
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unsigned int cycle_us;
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};
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static inline unsigned int baud_to_bit_ns(unsigned int baud)
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{
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return NSEC_PER_SEC / baud;
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}
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static inline unsigned int to_ns(unsigned int us)
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{
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return us * NSEC_PER_USEC;
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}
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/*
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* Set baud-rate, delay and tx-byte to create a 1-Wire pulse and adapt
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* the tx-byte according to the actual baud-rate.
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*
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* Reject when:
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* - time for a bit outside min/max range
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* - a 1-Wire response is not detectable for sent byte
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*/
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static int w1_uart_set_config(struct serdev_device *serdev,
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const struct w1_uart_limits *limits,
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struct w1_uart_config *w1cfg)
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{
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unsigned int packet_ns;
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unsigned int bits_low;
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unsigned int bit_ns;
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unsigned int low_ns;
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w1cfg->baudrate = serdev_device_set_baudrate(serdev, limits->baudrate);
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if (w1cfg->baudrate == 0)
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return -EINVAL;
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/* Compute in nanoseconds for accuracy */
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bit_ns = baud_to_bit_ns(w1cfg->baudrate);
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bits_low = to_ns(limits->bit_min_us) / bit_ns;
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/* start bit is always low */
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low_ns = bit_ns * (bits_low + 1);
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if (low_ns < to_ns(limits->bit_min_us))
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return -EINVAL;
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if (low_ns > to_ns(limits->bit_max_us))
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return -EINVAL;
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/* 1-Wire response detectable for sent byte */
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if (limits->sample_us > 0 &&
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bit_ns * BITS_PER_BYTE < low_ns + to_ns(limits->sample_us))
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return -EINVAL;
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/* delay: 1-Wire cycle takes longer than the UART packet */
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packet_ns = bit_ns * W1_UART_BITS_PER_PACKET;
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w1cfg->delay_us = 0;
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if (to_ns(limits->cycle_us) > packet_ns)
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w1cfg->delay_us =
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(to_ns(limits->cycle_us) - packet_ns) / NSEC_PER_USEC;
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/* byte to create 1-Wire pulse */
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w1cfg->tx_byte = 0xff << bits_low;
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return 0;
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}
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/*
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* Configuration for reset and presence detect
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* - bit_min_us is 480us, add margin and use 485us
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* - limits for sample time 60us-75us, use 65us
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*/
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static int w1_uart_set_config_reset(struct w1_uart_device *w1dev)
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{
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struct serdev_device *serdev = w1dev->serdev;
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struct device_node *np = serdev->dev.of_node;
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struct w1_uart_limits limits = { .baudrate = 9600,
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.bit_min_us = 485,
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.bit_max_us = 640,
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.sample_us = 65,
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.cycle_us = 960 };
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of_property_read_u32(np, "reset-bps", &limits.baudrate);
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return w1_uart_set_config(serdev, &limits, &w1dev->cfg_reset);
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}
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/*
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* Configuration for write-0 cycle (touch bit 0)
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* - bit_min_us is 60us, add margin and use 65us
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* - no sampling required, sample_us = 0
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*/
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static int w1_uart_set_config_touch_0(struct w1_uart_device *w1dev)
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{
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struct serdev_device *serdev = w1dev->serdev;
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struct device_node *np = serdev->dev.of_node;
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struct w1_uart_limits limits = { .baudrate = 115200,
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.bit_min_us = 65,
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.bit_max_us = 120,
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.sample_us = 0,
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.cycle_us = 70 };
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of_property_read_u32(np, "write-0-bps", &limits.baudrate);
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return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_0);
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}
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/*
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* Configuration for write-1 and read cycle (touch bit 1)
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* - bit_min_us is 5us, add margin and use 6us
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* - limits for sample time 5us-15us, use 15us
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*/
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static int w1_uart_set_config_touch_1(struct w1_uart_device *w1dev)
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{
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struct serdev_device *serdev = w1dev->serdev;
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struct device_node *np = serdev->dev.of_node;
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struct w1_uart_limits limits = { .baudrate = 115200,
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.bit_min_us = 6,
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.bit_max_us = 15,
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.sample_us = 15,
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.cycle_us = 70 };
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of_property_read_u32(np, "write-1-bps", &limits.baudrate);
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return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_1);
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}
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/*
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* Configure and open the serial device
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*/
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static int w1_uart_serdev_open(struct w1_uart_device *w1dev)
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{
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struct serdev_device *serdev = w1dev->serdev;
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struct device *dev = &serdev->dev;
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int ret;
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ret = devm_serdev_device_open(dev, serdev);
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if (ret < 0)
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return ret;
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ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
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if (ret < 0) {
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dev_err(dev, "set parity failed\n");
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return ret;
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}
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ret = w1_uart_set_config_reset(w1dev);
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if (ret < 0) {
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dev_err(dev, "config for reset failed\n");
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return ret;
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}
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ret = w1_uart_set_config_touch_0(w1dev);
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if (ret < 0) {
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dev_err(dev, "config for touch-0 failed\n");
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return ret;
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}
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ret = w1_uart_set_config_touch_1(w1dev);
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if (ret < 0) {
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dev_err(dev, "config for touch-1 failed\n");
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return ret;
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}
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serdev_device_set_flow_control(serdev, false);
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return 0;
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}
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/*
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* Send one byte (tx_byte) and read one byte (rx_byte) via serdev.
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*/
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static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
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const struct w1_uart_config *w1cfg, u8 *rx_byte)
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{
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struct serdev_device *serdev = w1dev->serdev;
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int ret;
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serdev_device_write_flush(serdev);
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serdev_device_set_baudrate(serdev, w1cfg->baudrate);
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/* write and immediately read one byte */
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reinit_completion(&w1dev->rx_byte_received);
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ret = serdev_device_write_buf(serdev, &w1cfg->tx_byte, 1);
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if (ret != 1)
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return -EIO;
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ret = wait_for_completion_interruptible_timeout(
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&w1dev->rx_byte_received, W1_UART_TIMEOUT);
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if (ret <= 0)
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return -EIO;
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/* locking could fail when serdev is unexpectedly receiving. */
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if (!mutex_trylock(&w1dev->rx_mutex))
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return -EIO;
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ret = w1dev->rx_err;
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if (ret == 0)
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*rx_byte = w1dev->rx_byte;
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mutex_unlock(&w1dev->rx_mutex);
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if (w1cfg->delay_us > 0)
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fsleep(w1cfg->delay_us);
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return ret;
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}
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static size_t w1_uart_serdev_receive_buf(struct serdev_device *serdev,
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const u8 *buf, size_t count)
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{
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struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
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mutex_lock(&w1dev->rx_mutex);
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/* sent a single byte and receive one single byte */
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if (count == 1) {
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w1dev->rx_byte = buf[0];
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w1dev->rx_err = 0;
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} else {
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w1dev->rx_err = -EIO;
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}
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mutex_unlock(&w1dev->rx_mutex);
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complete(&w1dev->rx_byte_received);
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return count;
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}
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static const struct serdev_device_ops w1_uart_serdev_ops = {
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.receive_buf = w1_uart_serdev_receive_buf,
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.write_wakeup = serdev_device_write_wakeup,
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};
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/*
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* 1-wire reset and presence detect: A present slave will manipulate
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* the received byte by pulling the 1-Wire low.
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*/
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static u8 w1_uart_reset_bus(void *data)
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{
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struct w1_uart_device *w1dev = data;
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const struct w1_uart_config *w1cfg = &w1dev->cfg_reset;
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int ret;
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u8 val;
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ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
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if (ret < 0)
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return -1;
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/* Device present (0) or no device (1) */
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return val != w1cfg->tx_byte ? 0 : 1;
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}
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/*
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* 1-Wire read and write cycle: Only the read-0 manipulates the
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* received byte, all others left the line untouched.
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*/
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static u8 w1_uart_touch_bit(void *data, u8 bit)
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{
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struct w1_uart_device *w1dev = data;
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const struct w1_uart_config *w1cfg = bit ? &w1dev->cfg_touch_1 :
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&w1dev->cfg_touch_0;
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int ret;
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u8 val;
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ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
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/* return inactive bus state on error */
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if (ret < 0)
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return 1;
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return val == w1cfg->tx_byte ? 1 : 0;
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}
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static int w1_uart_probe(struct serdev_device *serdev)
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{
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struct device *dev = &serdev->dev;
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struct w1_uart_device *w1dev;
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int ret;
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w1dev = devm_kzalloc(dev, sizeof(*w1dev), GFP_KERNEL);
|
||||
if (!w1dev)
|
||||
return -ENOMEM;
|
||||
w1dev->bus.data = w1dev;
|
||||
w1dev->bus.reset_bus = w1_uart_reset_bus;
|
||||
w1dev->bus.touch_bit = w1_uart_touch_bit;
|
||||
w1dev->serdev = serdev;
|
||||
|
||||
init_completion(&w1dev->rx_byte_received);
|
||||
mutex_init(&w1dev->rx_mutex);
|
||||
|
||||
ret = w1_uart_serdev_open(w1dev);
|
||||
if (ret < 0)
|
||||
return ret;
|
||||
serdev_device_set_drvdata(serdev, w1dev);
|
||||
serdev_device_set_client_ops(serdev, &w1_uart_serdev_ops);
|
||||
|
||||
return w1_add_master_device(&w1dev->bus);
|
||||
}
|
||||
|
||||
static void w1_uart_remove(struct serdev_device *serdev)
|
||||
{
|
||||
struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
|
||||
|
||||
/*
|
||||
* Waits until w1-uart callbacks are finished, serdev is closed
|
||||
* and its device data released automatically by devres (waits
|
||||
* until serdev-receive is finished).
|
||||
*/
|
||||
w1_remove_master_device(&w1dev->bus);
|
||||
}
|
||||
|
||||
static const struct of_device_id w1_uart_of_match[] = {
|
||||
{ .compatible = "w1-uart" },
|
||||
{},
|
||||
};
|
||||
MODULE_DEVICE_TABLE(of, w1_uart_of_match);
|
||||
|
||||
static struct serdev_device_driver w1_uart_driver = {
|
||||
.driver = {
|
||||
.name = "w1-uart",
|
||||
.of_match_table = w1_uart_of_match,
|
||||
},
|
||||
.probe = w1_uart_probe,
|
||||
.remove = w1_uart_remove,
|
||||
};
|
||||
|
||||
module_serdev_device_driver(w1_uart_driver);
|
||||
|
||||
MODULE_DESCRIPTION("UART w1 bus driver");
|
||||
MODULE_AUTHOR("Christoph Winklhofer <cj.winklhofer@gmail.com>");
|
||||
MODULE_LICENSE("GPL");
|
||||
Loading…
Reference in New Issue