[v5,3/3] w1: add UART w1 bus driver
Commit Message
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.
Signed-off-by: Christoph Winklhofer <cj.winklhofer@gmail.com>
---
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 | 402 +++++++++++++++++++++++++++++++++++
5 files changed, 468 insertions(+)
Comments
On 26/01/2024 16:42, 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.
>
..
> + * 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;
> + u8 tx_byte;
> +};
> +
> +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;
> + int rx_err;
> + u8 rx_byte;
> +
Missing documentation of mutex scope. What does it protect?
> + struct mutex mutex;
> +};
> +
..
> +/*
> + * Send one byte (tx_byte) and read one byte (rx_byte) via serdev.
> + */
> +static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
> + const struct w1_uart_config *w1cfg, u8 *rx_byte)
> +{
> + struct serdev_device *serdev = w1dev->serdev;
> + int ret;
> +
> + serdev_device_write_flush(serdev);
> + serdev_device_set_baudrate(serdev, w1cfg->baudrate);
> +
> + /* write and immediately read one byte */
> + reinit_completion(&w1dev->rx_byte_received);
> + ret = serdev_device_write_buf(serdev, &w1cfg->tx_byte, 1);
> + if (ret != 1)
> + return -EIO;
> + ret = wait_for_completion_interruptible_timeout(
> + &w1dev->rx_byte_received, W1_UART_TIMEOUT);
> + if (ret <= 0)
> + return -EIO;
> +
> + /* locking could fail during driver remove or when serdev is
It's not netdev, so:
/*
*
> + * unexpectedly in the receive callback.
> + */
> + if (!mutex_trylock(&w1dev->mutex))
> + return -EIO;
> +
> + ret = w1dev->rx_err;
> + if (ret == 0)
> + *rx_byte = w1dev->rx_byte;
> +
> + if (w1cfg->delay_us > 0)
> + fsleep(w1cfg->delay_us);
> +
> + mutex_unlock(&w1dev->mutex);
> +
> + return ret;
> +}
> +
> +static ssize_t w1_uart_serdev_receive_buf(struct serdev_device *serdev,
> + const u8 *buf, size_t count)
> +{
> + struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
> +
> + mutex_lock(&w1dev->mutex);
> +
> + /* sent a single byte and receive one single byte */
> + if (count == 1) {
> + w1dev->rx_byte = buf[0];
> + w1dev->rx_err = 0;
> + } else {
> + w1dev->rx_err = -EIO;
> + }
> +
> + mutex_unlock(&w1dev->mutex);
> + complete(&w1dev->rx_byte_received);
> +
> + return count;
> +}
> +
> +static const struct serdev_device_ops w1_uart_serdev_ops = {
> + .receive_buf = w1_uart_serdev_receive_buf,
> + .write_wakeup = serdev_device_write_wakeup,
> +};
> +
> +/*
> + * 1-wire reset and presence detect: A present slave will manipulate
> + * the received byte by pulling the 1-Wire low.
> + */
> +static u8 w1_uart_reset_bus(void *data)
> +{
> + struct w1_uart_device *w1dev = data;
> + const struct w1_uart_config *w1cfg = &w1dev->cfg_reset;
> + int ret;
> + u8 val;
> +
> + ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
> + if (ret < 0)
> + return -1;
> +
> + /* Device present (0) or no device (1) */
> + return val != w1cfg->tx_byte ? 0 : 1;
> +}
> +
> +/*
> + * 1-Wire read and write cycle: Only the read-0 manipulates the
> + * received byte, all others left the line untouched.
> + */
> +static u8 w1_uart_touch_bit(void *data, u8 bit)
> +{
> + struct w1_uart_device *w1dev = data;
> + const struct w1_uart_config *w1cfg = bit ? &w1dev->cfg_touch_1 :
> + &w1dev->cfg_touch_0;
> + int ret;
> + u8 val;
> +
> + ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
> +
> + /* return inactive bus state on error */
> + if (ret < 0)
> + return 1;
> +
> + return val == w1cfg->tx_byte ? 1 : 0;
> +}
> +
> +static int w1_uart_probe(struct serdev_device *serdev)
> +{
> + struct device *dev = &serdev->dev;
> + struct w1_uart_device *w1dev;
> + int ret;
> +
> + 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->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);
> +
> + mutex_lock(&w1dev->mutex);
> +
> + w1_remove_master_device(&w1dev->bus);
> +
> + mutex_unlock(&w1dev->mutex);
This is still suspicious. You do not have serdev_device_close and you
want to protect from concurrent access but it looks insufficient.
This code assumes that:
w1_uart_remove()
<-- here concurrent read/write might start
mutex_lock()
w1_remove_master_device()
mutex_unlock()
<-- now w1_uart_serdev_tx_rx() or w1_uart_serdev_receive_buf() can be
executed, but device is removed. So what's the point of the mutex here?
What exactly is protected by the mutex? So far it looks like only some
contents of w1dev, but it does not matter, because it that memory is
still valid at this point.
After describing what is protected we can think whether it is really
protected...
>
Best regards,
Krzysztof
On Wed, Jan 31, 2024 at 02:12:34PM +0100, Krzysztof Kozlowski wrote:
> On 26/01/2024 16:42, 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.
> >
>
> ...
>
> > + * 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;
> > + u8 tx_byte;
> > +};
> > +
> > +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;
> > + int rx_err;
> > + u8 rx_byte;
> > +
>
> Missing documentation of mutex scope. What does it protect?
>
The mutex should protect concurrent access to rx_err and rx_byte. It
would be not be required in the good case: a write is initiated solely
by the w1-callbacks in 'w1_uart_serdev_tx_rx' and a completion is used
to wait for the result of serdev-receive.
However, in case the UART is not configured as a loop, a serdev-receive
may occur when w1_uart_serdev_tx_rx evaluates rx_err and rx_byte in
w1_uart_serdev_tx_rx, so it is protected - however, I will try to find
a better way to detect such an error.
In addition, the w1-callbacks should also return during a 'remove' (with
the mutex_try_lock) - see comment on that below.
> > + struct mutex mutex;
> > +};
> > +
>
> ...
>
> > +/*
> > + * Send one byte (tx_byte) and read one byte (rx_byte) via serdev.
> > + */
> > +static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
> > + const struct w1_uart_config *w1cfg, u8 *rx_byte)
> > +{
> > + struct serdev_device *serdev = w1dev->serdev;
> > + int ret;
> > +
> > + serdev_device_write_flush(serdev);
> > + serdev_device_set_baudrate(serdev, w1cfg->baudrate);
> > +
> > + /* write and immediately read one byte */
> > + reinit_completion(&w1dev->rx_byte_received);
> > + ret = serdev_device_write_buf(serdev, &w1cfg->tx_byte, 1);
> > + if (ret != 1)
> > + return -EIO;
> > + ret = wait_for_completion_interruptible_timeout(
> > + &w1dev->rx_byte_received, W1_UART_TIMEOUT);
> > + if (ret <= 0)
> > + return -EIO;
> > +
> > + /* locking could fail during driver remove or when serdev is
>
> It's not netdev, so:
> /*
> *
>
Ok.
> > + * unexpectedly in the receive callback.
> > + */
> > + if (!mutex_trylock(&w1dev->mutex))
> > + return -EIO;
> > +
> > + ret = w1dev->rx_err;
> > + if (ret == 0)
> > + *rx_byte = w1dev->rx_byte;
> > +
> > + if (w1cfg->delay_us > 0)
> > + fsleep(w1cfg->delay_us);
> > +
> > + mutex_unlock(&w1dev->mutex);
> > +
> > + return ret;
> > +}
> > +
> > +static ssize_t w1_uart_serdev_receive_buf(struct serdev_device *serdev,
> > + const u8 *buf, size_t count)
> > +{
> > + struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
> > +
> > + mutex_lock(&w1dev->mutex);
> > +
> > + /* sent a single byte and receive one single byte */
> > + if (count == 1) {
> > + w1dev->rx_byte = buf[0];
> > + w1dev->rx_err = 0;
> > + } else {
> > + w1dev->rx_err = -EIO;
> > + }
> > +
> > + mutex_unlock(&w1dev->mutex);
> > + complete(&w1dev->rx_byte_received);
> > +
> > + return count;
> > +}
> > +
> > +static const struct serdev_device_ops w1_uart_serdev_ops = {
> > + .receive_buf = w1_uart_serdev_receive_buf,
> > + .write_wakeup = serdev_device_write_wakeup,
> > +};
> > +
> > +/*
> > + * 1-wire reset and presence detect: A present slave will manipulate
> > + * the received byte by pulling the 1-Wire low.
> > + */
> > +static u8 w1_uart_reset_bus(void *data)
> > +{
> > + struct w1_uart_device *w1dev = data;
> > + const struct w1_uart_config *w1cfg = &w1dev->cfg_reset;
> > + int ret;
> > + u8 val;
> > +
> > + ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
> > + if (ret < 0)
> > + return -1;
> > +
> > + /* Device present (0) or no device (1) */
> > + return val != w1cfg->tx_byte ? 0 : 1;
> > +}
> > +
> > +/*
> > + * 1-Wire read and write cycle: Only the read-0 manipulates the
> > + * received byte, all others left the line untouched.
> > + */
> > +static u8 w1_uart_touch_bit(void *data, u8 bit)
> > +{
> > + struct w1_uart_device *w1dev = data;
> > + const struct w1_uart_config *w1cfg = bit ? &w1dev->cfg_touch_1 :
> > + &w1dev->cfg_touch_0;
> > + int ret;
> > + u8 val;
> > +
> > + ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
> > +
> > + /* return inactive bus state on error */
> > + if (ret < 0)
> > + return 1;
> > +
> > + return val == w1cfg->tx_byte ? 1 : 0;
> > +}
> > +
> > +static int w1_uart_probe(struct serdev_device *serdev)
> > +{
> > + struct device *dev = &serdev->dev;
> > + struct w1_uart_device *w1dev;
> > + int ret;
> > +
> > + 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->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);
> > +
> > + mutex_lock(&w1dev->mutex);
> > +
> > + w1_remove_master_device(&w1dev->bus);
> > +
> > + mutex_unlock(&w1dev->mutex);
>
> This is still suspicious. You do not have serdev_device_close and you
> want to protect from concurrent access but it looks insufficient.
>
> This code assumes that:
>
> w1_uart_remove()
> <-- here concurrent read/write might start
> mutex_lock()
> w1_remove_master_device()
> mutex_unlock()
> <-- now w1_uart_serdev_tx_rx() or w1_uart_serdev_receive_buf() can be
> executed, but device is removed. So what's the point of the mutex here?
>
> What exactly is protected by the mutex? So far it looks like only some
> contents of w1dev, but it does not matter, because it that memory is
> still valid at this point.
>
> After describing what is protected we can think whether it is really
> protected...
>
>
> >
>
> Best regards,
> Krzysztof
>
Yes, it is still suspicious, sorry..
After w1_uart_remove, serdev is closed and w1dev is released. Therefore
the w1-callback (w1_uart_serdev_tx_rx) must be finished before returning
from w1_uart_remove. That was the intention with the lock and trylock.
I thought that after w1_remove_master_device, the w1-callback
(w1_uart_serdev_tx_rx) is finished which is not the case. I will check
the working of w1_remove_master_device, probably it requires a lock to
a mutex from w1-bus.
Many thanks for your review and pointing the things out!
Kind regards,
Christoph
On 01/02/2024 08:29, Christoph Winklhofer wrote:
>>> +
>>> +static void w1_uart_remove(struct serdev_device *serdev)
>>> +{
>>> + struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
>>> +
>>> + mutex_lock(&w1dev->mutex);
>>> +
>>> + w1_remove_master_device(&w1dev->bus);
>>> +
>>> + mutex_unlock(&w1dev->mutex);
>>
>> This is still suspicious. You do not have serdev_device_close and you
>> want to protect from concurrent access but it looks insufficient.
>>
>> This code assumes that:
>>
>> w1_uart_remove()
>> <-- here concurrent read/write might start
>> mutex_lock()
>> w1_remove_master_device()
>> mutex_unlock()
>> <-- now w1_uart_serdev_tx_rx() or w1_uart_serdev_receive_buf() can be
>> executed, but device is removed. So what's the point of the mutex here?
>>
>> What exactly is protected by the mutex? So far it looks like only some
>> contents of w1dev, but it does not matter, because it that memory is
>> still valid at this point.
>>
>> After describing what is protected we can think whether it is really
>> protected...
>>
>>
>>>
>>
>> Best regards,
>> Krzysztof
>>
>
> Yes, it is still suspicious, sorry..
>
> After w1_uart_remove, serdev is closed and w1dev is released. Therefore
> the w1-callback (w1_uart_serdev_tx_rx) must be finished before returning
I did not even go to end of w1_uart_remove(). In my code above, that
thread is still in w1_uart_remove(), just after unlocking mutex.
> from w1_uart_remove. That was the intention with the lock and trylock.
Then it does not look really protected. To be honest, w1-gpio and other
drivers also might have a race here. You can test it by adding long
sleeps in read/write paths and then trying to unbind device. Maybe this
should be fixed everywhere, but this mutex here brings more questions.
Best regards,
Krzysztof
On Thu, Feb 01, 2024 at 10:35:32AM +0100, Krzysztof Kozlowski wrote:
> On 01/02/2024 08:29, Christoph Winklhofer wrote:
> >>> +
> >>> +static void w1_uart_remove(struct serdev_device *serdev)
> >>> +{
> >>> + struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
> >>> +
> >>> + mutex_lock(&w1dev->mutex);
> >>> +
> >>> + w1_remove_master_device(&w1dev->bus);
> >>> +
> >>> + mutex_unlock(&w1dev->mutex);
> >>
> >> This is still suspicious. You do not have serdev_device_close and you
> >> want to protect from concurrent access but it looks insufficient.
> >>
> >> This code assumes that:
> >>
> >> w1_uart_remove()
> >> <-- here concurrent read/write might start
> >> mutex_lock()
> >> w1_remove_master_device()
> >> mutex_unlock()
> >> <-- now w1_uart_serdev_tx_rx() or w1_uart_serdev_receive_buf() can be
> >> executed, but device is removed. So what's the point of the mutex here?
> >>
> >> What exactly is protected by the mutex? So far it looks like only some
> >> contents of w1dev, but it does not matter, because it that memory is
> >> still valid at this point.
> >>
> >> After describing what is protected we can think whether it is really
> >> protected...
> >>
> >>
> >>>
> >>
> >> Best regards,
> >> Krzysztof
> >>
> >
> > Yes, it is still suspicious, sorry..
> >
> > After w1_uart_remove, serdev is closed and w1dev is released. Therefore
> > the w1-callback (w1_uart_serdev_tx_rx) must be finished before returning
>
> I did not even go to end of w1_uart_remove(). In my code above, that
> thread is still in w1_uart_remove(), just after unlocking mutex.
>
Ok, I looked more closely at the underlying w1-code and think it is
sufficient to only call w1_remove_master_device() in w1_uart_remove.
This function waits until all slaves have finished their work, so
w1_uart_serdev_tx_rx finished too. The lock is not required.
Hence, I will use the mutex only to protected concurrent access of
serdev and w1-callbacks (for rx_byte and rx_err).
> > from w1_uart_remove. That was the intention with the lock and trylock.
>
> Then it does not look really protected. To be honest, w1-gpio and other
> drivers also might have a race here. You can test it by adding long
> sleeps in read/write paths and then trying to unbind device. Maybe this
> should be fixed everywhere, but this mutex here brings more questions.
>
I added a delay, unbind takes longer but works without problems when its
done during a temperature read.
IMO also the other drivers should be fine. From w1_int.c: The w1_master
is ref-counted and released when it is unused (2). In w1_slave_detach
(1), the slaves decrement this count, perform specific clean up (in
remove_slave) and remove sysfs entries.
w1_int.c:
void __w1_remove_master_device(struct w1_master *dev)
..
list_for_each_entry_safe(sl, sln, &dev->slist, w1_slave_entry) {
mutex_unlock(&dev->list_mutex);
w1_slave_detach(sl); (1)
..
while (atomic_read(&dev->refcnt)) { (2)
..
}
..
w1_free_dev(dev);
For example w1_therm waits in remove_slave until its w1-operations are
done. The other slave-drivers (e.g. w1_ds2405.c) use w1-operations in
their sysfs-callback and I suppose that sysfs-removal waits until the
sysfs-read is finished.
Kind regards,
Christoph
@@ -12,3 +12,4 @@
mxc-w1
omap-hdq
w1-gpio
+ w1-uart
new file mode 100644
@@ -0,0 +1,54 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+=====================
+Kernel driver w1-uart
+=====================
+
+Author: Christoph Winklhofer <cj.winklhofer@gmail.com>
+
+
+Description
+-----------
+
+UART 1-Wire bus driver. The driver utilizes the UART interface via the
+Serial Device Bus to create the 1-Wire timing patterns as described in
+the document `"Using a UART to Implement a 1-Wire Bus Master"`_.
+
+.. _"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
+
+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 0x80 is used for a
+Write-0 operation (low time 69.6us) and the byte 0xff for Read-0, Read-1
+and Write-1 (low time 8.7us).
+
+The default baud-rate for reset and presence detection is 9600 and for
+a 1-Wire read or write operation 115200. In case the actual baud-rate
+is different from the requested one, the transmitted byte is adapted
+to generate the 1-Wire timing patterns.
+
+
+Usage
+-----
+
+Specify the UART 1-wire bus in the device tree by adding the single child
+onewire to the serial node (e.g. uart0). For example:
+::
+
+ @uart0 {
+ ...
+ onewire {
+ compatible = "w1-uart";
+ };
+ };
@@ -78,5 +78,15 @@ config W1_MASTER_SGI
This support is also available as a module. If so, the module
will be called sgi_w1.
+config W1_MASTER_UART
+ tristate "UART 1-wire driver"
+ depends on SERIAL_DEV_BUS
+ help
+ Say Y here if you want to communicate with your 1-wire devices using
+ UART interface.
+
+ This support is also available as a module. If so, the module
+ will be called w1-uart.
+
endmenu
@@ -12,3 +12,4 @@ obj-$(CONFIG_W1_MASTER_MXC) += mxc_w1.o
obj-$(CONFIG_W1_MASTER_GPIO) += w1-gpio.o
obj-$(CONFIG_HDQ_MASTER_OMAP) += omap_hdq.o
obj-$(CONFIG_W1_MASTER_SGI) += sgi_w1.o
+obj-$(CONFIG_W1_MASTER_UART) += w1-uart.o
new file mode 100644
@@ -0,0 +1,402 @@
+// 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>
+
+/* UART packet contains start and stop bit */
+#define W1_UART_BITS_PER_PACKET (BITS_PER_BYTE + 2)
+
+#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;
+ u8 tx_byte;
+};
+
+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;
+ int rx_err;
+ u8 rx_byte;
+
+ 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 NSEC_PER_SEC / baud;
+}
+
+static inline unsigned int to_ns(unsigned int us)
+{
+ return us * 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 packet_ns;
+ 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 * BITS_PER_BYTE < low_ns + to_ns(limits->sample_us))
+ return -EINVAL;
+
+ /* delay: 1-Wire cycle takes longer than the UART packet */
+ packet_ns = bit_ns * W1_UART_BITS_PER_PACKET;
+ w1cfg->delay_us = 0;
+ if (to_ns(limits->cycle_us) > packet_ns)
+ w1cfg->delay_us =
+ (to_ns(limits->cycle_us) - packet_ns) / NSEC_PER_USEC;
+
+ /* byte to create 1-Wire pulse */
+ w1cfg->tx_byte = 0xff << bits_low;
+
+ return 0;
+}
+
+/*
+ * Configuration for reset and presence detect
+ * - bit_min_us is 480us, add margin and use 485us
+ * - limits for sample time 60us-75us, use 65us
+ */
+static int w1_uart_set_config_reset(struct w1_uart_device *w1dev)
+{
+ struct serdev_device *serdev = w1dev->serdev;
+ struct device_node *np = serdev->dev.of_node;
+
+ struct w1_uart_limits limits = { .baudrate = 9600,
+ .bit_min_us = 485,
+ .bit_max_us = 640,
+ .sample_us = 65,
+ .cycle_us = 960 };
+
+ of_property_read_u32(np, "reset-bps", &limits.baudrate);
+
+ return w1_uart_set_config(serdev, &limits, &w1dev->cfg_reset);
+}
+
+/*
+ * Configuration for write-0 cycle (touch bit 0)
+ * - bit_min_us is 60us, add margin and use 65us
+ * - no sampling required, sample_us = 0
+ */
+static int w1_uart_set_config_touch_0(struct w1_uart_device *w1dev)
+{
+ struct serdev_device *serdev = w1dev->serdev;
+ struct device_node *np = serdev->dev.of_node;
+
+ struct w1_uart_limits limits = { .baudrate = 115200,
+ .bit_min_us = 65,
+ .bit_max_us = 120,
+ .sample_us = 0,
+ .cycle_us = 70 };
+
+ of_property_read_u32(np, "write-0-bps", &limits.baudrate);
+
+ return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_0);
+}
+
+/*
+ * Configuration for write-1 and read cycle (touch bit 1)
+ * - bit_min_us is 5us, add margin and use 6us
+ * - limits for sample time 5us-15us, use 15us
+ */
+static int w1_uart_set_config_touch_1(struct w1_uart_device *w1dev)
+{
+ struct serdev_device *serdev = w1dev->serdev;
+ struct device_node *np = serdev->dev.of_node;
+
+ struct w1_uart_limits limits = { .baudrate = 115200,
+ .bit_min_us = 6,
+ .bit_max_us = 15,
+ .sample_us = 15,
+ .cycle_us = 70 };
+
+ of_property_read_u32(np, "write-1-bps", &limits.baudrate);
+
+ return w1_uart_set_config(serdev, &limits, &w1dev->cfg_touch_1);
+}
+
+/*
+ * Configure and open the serial device
+ */
+static int w1_uart_serdev_open(struct w1_uart_device *w1dev)
+{
+ struct serdev_device *serdev = w1dev->serdev;
+ struct device *dev = &serdev->dev;
+ int ret;
+
+ ret = devm_serdev_device_open(dev, serdev);
+ if (ret < 0)
+ return ret;
+
+ ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
+ if (ret < 0) {
+ dev_err(dev, "set parity failed\n");
+ return ret;
+ }
+
+ ret = w1_uart_set_config_reset(w1dev);
+ if (ret < 0) {
+ dev_err(dev, "config for reset failed\n");
+ return ret;
+ }
+
+ ret = w1_uart_set_config_touch_0(w1dev);
+ if (ret < 0) {
+ dev_err(dev, "config for touch-0 failed\n");
+ return ret;
+ }
+
+ ret = w1_uart_set_config_touch_1(w1dev);
+ if (ret < 0) {
+ dev_err(dev, "config for touch-1 failed\n");
+ return ret;
+ }
+
+ serdev_device_set_flow_control(serdev, false);
+
+ return 0;
+}
+
+/*
+ * Send one byte (tx_byte) and read one byte (rx_byte) via serdev.
+ */
+static int w1_uart_serdev_tx_rx(struct w1_uart_device *w1dev,
+ const struct w1_uart_config *w1cfg, u8 *rx_byte)
+{
+ struct serdev_device *serdev = w1dev->serdev;
+ int ret;
+
+ serdev_device_write_flush(serdev);
+ serdev_device_set_baudrate(serdev, w1cfg->baudrate);
+
+ /* write and immediately read one byte */
+ reinit_completion(&w1dev->rx_byte_received);
+ ret = serdev_device_write_buf(serdev, &w1cfg->tx_byte, 1);
+ if (ret != 1)
+ return -EIO;
+ ret = wait_for_completion_interruptible_timeout(
+ &w1dev->rx_byte_received, W1_UART_TIMEOUT);
+ if (ret <= 0)
+ return -EIO;
+
+ /* locking could fail during driver remove or when serdev is
+ * unexpectedly in the receive callback.
+ */
+ if (!mutex_trylock(&w1dev->mutex))
+ return -EIO;
+
+ ret = w1dev->rx_err;
+ if (ret == 0)
+ *rx_byte = w1dev->rx_byte;
+
+ if (w1cfg->delay_us > 0)
+ fsleep(w1cfg->delay_us);
+
+ mutex_unlock(&w1dev->mutex);
+
+ return ret;
+}
+
+static ssize_t w1_uart_serdev_receive_buf(struct serdev_device *serdev,
+ const u8 *buf, size_t count)
+{
+ struct w1_uart_device *w1dev = serdev_device_get_drvdata(serdev);
+
+ mutex_lock(&w1dev->mutex);
+
+ /* sent a single byte and receive one single byte */
+ if (count == 1) {
+ w1dev->rx_byte = buf[0];
+ w1dev->rx_err = 0;
+ } else {
+ w1dev->rx_err = -EIO;
+ }
+
+ mutex_unlock(&w1dev->mutex);
+ complete(&w1dev->rx_byte_received);
+
+ return count;
+}
+
+static const struct serdev_device_ops w1_uart_serdev_ops = {
+ .receive_buf = w1_uart_serdev_receive_buf,
+ .write_wakeup = serdev_device_write_wakeup,
+};
+
+/*
+ * 1-wire reset and presence detect: A present slave will manipulate
+ * the received byte by pulling the 1-Wire low.
+ */
+static u8 w1_uart_reset_bus(void *data)
+{
+ struct w1_uart_device *w1dev = data;
+ const struct w1_uart_config *w1cfg = &w1dev->cfg_reset;
+ int ret;
+ u8 val;
+
+ ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
+ if (ret < 0)
+ return -1;
+
+ /* Device present (0) or no device (1) */
+ return val != w1cfg->tx_byte ? 0 : 1;
+}
+
+/*
+ * 1-Wire read and write cycle: Only the read-0 manipulates the
+ * received byte, all others left the line untouched.
+ */
+static u8 w1_uart_touch_bit(void *data, u8 bit)
+{
+ struct w1_uart_device *w1dev = data;
+ const struct w1_uart_config *w1cfg = bit ? &w1dev->cfg_touch_1 :
+ &w1dev->cfg_touch_0;
+ int ret;
+ u8 val;
+
+ ret = w1_uart_serdev_tx_rx(w1dev, w1cfg, &val);
+
+ /* return inactive bus state on error */
+ if (ret < 0)
+ return 1;
+
+ return val == w1cfg->tx_byte ? 1 : 0;
+}
+
+static int w1_uart_probe(struct serdev_device *serdev)
+{
+ struct device *dev = &serdev->dev;
+ struct w1_uart_device *w1dev;
+ int ret;
+
+ 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->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);
+
+ mutex_lock(&w1dev->mutex);
+
+ w1_remove_master_device(&w1dev->bus);
+
+ mutex_unlock(&w1dev->mutex);
+}
+
+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");