This extends the user interface for rs485 communication:
We add a new flag, SER_RS485_DELAY_IN_USEC, to struct serial_rs485 that
indicates that delay_rts_before_send and delay_rts_after_send values are
interpreted in microsecond units.
Up until now, the code comment defined these values to hold the delays in
millisecond units. Especially with fast data rates (1Mbaut or more) that
are not too uncommon for RS485, 1ms become quite long. Users need to be
able to set shorter delays than 1 ms in order not to slow down the channel
unnecessarily.
So when delays are needed, but not as long as 1ms, this enables faster
communication channels without changing the baudrate.
Signed-off-by: Martin Kepplinger <[email protected]>
---
Hi,
We have this totally quirky patch that uses udelay() in our tree
for a looong time now because of the above reasons - and because we are lazy.
This is an attempt to get rid of said patch on our side and fix this properly.
What do you thing about adding a flag in general?
The following patches should integrate this idea in devicetree and drivers.
These changes are NOT tested on hardware but should behave predictably
enough. I use the delays in a driver that doesn't implement them yet at
all. I'll do that after this (or something similar) is merged - it's a 2-liner
then.
Also, a patch to the rs485conf tool, that is sometimes used instead of
ioctl() directly, will be prepared as well.
thanks
martin
include/uapi/linux/serial.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
index 93eb3c496ff1..c16c950ebca2 100644
--- a/include/uapi/linux/serial.h
+++ b/include/uapi/linux/serial.h
@@ -126,8 +126,15 @@ struct serial_rs485 {
#define SER_RS485_TERMINATE_BUS (1 << 5) /* Enable bus
termination
(if supported) */
- __u32 delay_rts_before_send; /* Delay before send (milliseconds) */
- __u32 delay_rts_after_send; /* Delay after send (milliseconds) */
+#define SER_RS485_DELAY_IN_USEC (1 << 6) /* delay_rts_*_send
+ values are given in
+ microseconds */
+ __u32 delay_rts_before_send; /* Delay before send (milliseconds
+ by default. microseconds if flag
+ is set) */
+ __u32 delay_rts_after_send; /* Delay after send (milliseconds
+ by default. microseconds if flag
+ is set) */
__u32 padding[5]; /* Memory is cheap, new structs
are a royal PITA .. */
};
--
2.20.1
Document the new RS485 flag, SER_RS485_DELAY_IN_USEC that specifies that the
rts delay values stored in struct serial_rs485 hold values in microseconds
instead of milliseconds (the default).
Signed-off-by: Martin Kepplinger <[email protected]>
---
Documentation/serial/serial-rs485.txt | 3 +++
1 file changed, 3 insertions(+)
diff --git a/Documentation/serial/serial-rs485.txt b/Documentation/serial/serial-rs485.txt
index ce0c1a9b8aab..a1e15e9efc2e 100644
--- a/Documentation/serial/serial-rs485.txt
+++ b/Documentation/serial/serial-rs485.txt
@@ -75,6 +75,9 @@
/* Set rts delay after send, if needed: */
rs485conf.delay_rts_after_send = ...;
+ /* Specify the rts delay to be microseconds, not milliseconds */
+ rs485conf.flags |= SER_RS485_DELAY_IN_USEC;
+
/* Set this flag if you want to receive data even while sending data */
rs485conf.flags |= SER_RS485_RX_DURING_TX;
--
2.20.1
Read struct serial_rs485's flag SER_RS485_DELAY_IN_USEC and apply the delay
accordingly.
Signed-off-by: Martin Kepplinger <[email protected]>
---
drivers/tty/serial/omap-serial.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 6420ae581a80..adcd75ce5112 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -310,7 +310,11 @@ static void serial_omap_stop_tx(struct uart_port *port)
res = (port->rs485.flags & SER_RS485_RTS_AFTER_SEND) ?
1 : 0;
if (gpio_get_value(up->rts_gpio) != res) {
- if (port->rs485.delay_rts_after_send > 0)
+ if (port->rs485.delay_rts_after_send > 0 &&
+ port->rs485.flags & SER_RS485_DELAY_IN_USEC)
+ udelay(
+ port->rs485.delay_rts_after_send);
+ else if (port->rs485.delay_rts_after_send > 0)
mdelay(
port->rs485.delay_rts_after_send);
gpio_set_value(up->rts_gpio, res);
@@ -420,7 +424,11 @@ static void serial_omap_start_tx(struct uart_port *port)
res = (port->rs485.flags & SER_RS485_RTS_ON_SEND) ? 1 : 0;
if (gpio_get_value(up->rts_gpio) != res) {
gpio_set_value(up->rts_gpio, res);
- if (port->rs485.delay_rts_before_send > 0)
+ if (port->rs485.delay_rts_before_send > 0 &&
+ port->rs485.flags & SER_RS485_DELAY_IN_USEC)
+ udelay(port->rs485.delay_rts_before_send);
+ else if (port->rs485.delay_rts_before_send > 0 &&
+ !(port->rs485.flags & SER_RS485_DELAY_IN_USEC)
mdelay(port->rs485.delay_rts_before_send);
}
}
@@ -1407,8 +1415,17 @@ serial_omap_config_rs485(struct uart_port *port, struct serial_rs485 *rs485)
serial_out(up, UART_IER, 0);
/* Clamp the delays to [0, 100ms] */
- rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
- rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
+ if (port->rs485.flags & SER_RS485_DELAY_IN_USEC) {
+ rs485->delay_rts_before_send = min(rs485->delay_rts_before_send,
+ 100000U);
+ rs485->delay_rts_after_send = min(rs485->delay_rts_after_send,
+ 100000U);
+ } else {
+ rs485->delay_rts_before_send = min(rs485->delay_rts_before_send,
+ 100);
+ rs485->delay_rts_after_send = min(rs485->delay_rts_after_send,
+ 100U);
+ }
/* store new config */
port->rs485 = *rs485;
--
2.20.1
struct serial_rs485 now optionally holds the rts delay values in
microseconds. Users can set these delays in their devicetree descriptions,
so this adds the microseconds-option with the "rs485-rts-delay-us" boolean
property.
Signed-off-by: Martin Kepplinger <[email protected]>
---
Documentation/devicetree/bindings/serial/rs485.txt | 1 +
drivers/tty/serial/serial_core.c | 11 +++++++++++
2 files changed, 12 insertions(+)
diff --git a/Documentation/devicetree/bindings/serial/rs485.txt b/Documentation/devicetree/bindings/serial/rs485.txt
index b92592dff6dd..77396c62b383 100644
--- a/Documentation/devicetree/bindings/serial/rs485.txt
+++ b/Documentation/devicetree/bindings/serial/rs485.txt
@@ -12,6 +12,7 @@ Optional properties:
* b is the delay between end of data sent and rts signal in milliseconds
it corresponds to the delay after sending data and actual release of the line.
If this property is not specified, <0 0> is assumed.
+- rs485-rts-delay-us: the same as rs485-rts-delay, but in microseconds.
- rs485-rts-active-low: drive RTS low when sending (default is high).
- linux,rs485-enabled-at-boot-time: empty property telling to enable the rs485
feature at boot time. It can be disabled later with proper ioctl.
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 556f50aa1b58..4fb265b2c0fe 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3097,6 +3097,17 @@ void uart_get_rs485_mode(struct device *dev, struct serial_rs485 *rs485conf)
rs485conf->delay_rts_after_send = 0;
}
+ ret = device_property_read_u32_array(dev, "rs485-rts-delay-us",
+ rs485_delay, 2);
+ if (!ret) {
+ rs485conf->delay_rts_before_send = rs485_delay[0];
+ rs485conf->delay_rts_after_send = rs485_delay[1];
+ rs485conf->flags |= SER_RS485_DELAY_IN_USEC;
+ } else {
+ rs485conf->delay_rts_before_send = 0;
+ rs485conf->delay_rts_after_send = 0;
+ }
+
/*
* Clear full-duplex and enabled flags, set RTS polarity to active high
* to get to a defined state with the following properties:
--
2.20.1
Read struct serial_rs485's flag SER_RS485_DELAY_IN_USEC and apply the delay
accordingly.
Signed-off-by: Martin Kepplinger <[email protected]>
---
drivers/tty/serial/8250/8250_omap.c | 13 +++++++++++--
drivers/tty/serial/8250/8250_port.c | 25 +++++++++++++++++++++----
2 files changed, 32 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 0a8316632d75..cbce43ac60b1 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -720,8 +720,17 @@ static int omap_8250_rs485_config(struct uart_port *port,
struct uart_8250_port *up = up_to_u8250p(port);
/* Clamp the delays to [0, 100ms] */
- rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
- rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
+ if (rs485->flags & SER_RS485_DELAY_IN_USEC) {
+ rs485->delay_rts_before_send = min(rs485->delay_rts_before_send,
+ 100000U);
+ rs485->delay_rts_after_send = min(rs485->delay_rts_after_send,
+ 100000U);
+ } else {
+ rs485->delay_rts_before_send = min(rs485->delay_rts_before_send,
+ 100U);
+ rs485->delay_rts_after_send = min(rs485->delay_rts_after_send,
+ 100U);
+ }
port->rs485 = *rs485;
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index d2f3310abe54..0cee4aa8323d 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1483,6 +1483,15 @@ static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
hrtimer_start(hrt, t, HRTIMER_MODE_REL);
}
+static void start_hrtimer_us(struct hrtimer *hrt, unsigned long usec)
+{
+ long sec = usec / 1000000;
+ long nsec = (usec % 1000000) * 1000000000;
+ ktime_t t = ktime_set(sec, nsec);
+
+ hrtimer_start(hrt, t, HRTIMER_MODE_REL);
+}
+
static void __stop_tx_rs485(struct uart_8250_port *p)
{
struct uart_8250_em485 *em485 = p->em485;
@@ -1493,8 +1502,12 @@ static void __stop_tx_rs485(struct uart_8250_port *p)
*/
if (p->port.rs485.delay_rts_after_send > 0) {
em485->active_timer = &em485->stop_tx_timer;
- start_hrtimer_ms(&em485->stop_tx_timer,
- p->port.rs485.delay_rts_after_send);
+ if (p->port.rs485.flags & SER_RS485_DELAY_IN_USEC)
+ start_hrtimer_us(&em485->stop_tx_timer,
+ p->port.rs485.delay_rts_after_send);
+ else
+ start_hrtimer_ms(&em485->stop_tx_timer,
+ p->port.rs485.delay_rts_after_send);
} else {
__do_stop_tx_rs485(p);
}
@@ -1600,8 +1613,12 @@ static inline void start_tx_rs485(struct uart_port *port)
if (up->port.rs485.delay_rts_before_send > 0) {
em485->active_timer = &em485->start_tx_timer;
- start_hrtimer_ms(&em485->start_tx_timer,
- up->port.rs485.delay_rts_before_send);
+ if (up->port.rs485.flags & SER_RS485_DELAY_IN_USEC)
+ start_hrtimer_us(&em485->start_tx_timer,
+ up->port.rs485.delay_rts_before_send);
+ else
+ start_hrtimer_ms(&em485->start_tx_timer,
+ up->port.rs485.delay_rts_before_send);
return;
}
}
--
2.20.1