[PATCH v5 0/3] tty: Introduce software RS485 direction control support

[PATCH v5 0/3] tty: Introduce software RS485 direction control support

[Matwey V. Kornilov]

Changes from v4:
 - Add commit message to 1/3
Changes from v3:
 - Completely redesigned.
Changes from v2:
 - Introduced SER_RS485_SOFTWARE to show that software implementation is being used
 - serial8250_rs485_config is located as required
 - Timers are used to implement delay_before and delay_after timeouts

[PATCH v5 1/3] tty: Move serial8250_stop_rx in front of serial8250_start_tx

[Matwey V. Kornilov]

Software RS485 emultaion is to be added in the following commit.
serial8250_start_tx will need to refer serial8250_stop_rx.
Move serial8250_stop_rx in front of serial8250_start_tx in order
to avoid function forward declaration.

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
---
 drivers/tty/serial/8250/8250_port.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 0bbf340..8ad0b2d 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1280,6 +1280,19 @@ static void autoconfig_irq(struct uart_8250_port *up)
 	port->irq = (irq > 0) ? irq : 0;
 }
 
+static void serial8250_stop_rx(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+
+	serial8250_rpm_get(up);
+
+	up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
+	up->port.read_status_mask &= ~UART_LSR_DR;
+	serial_port_out(port, UART_IER, up->ier);
+
+	serial8250_rpm_put(up);
+}
+
 static inline void __stop_tx(struct uart_8250_port *p)
 {
 	if (p->ier & UART_IER_THRI) {
@@ -1347,19 +1360,6 @@ static void serial8250_unthrottle(struct uart_port *port)
 	port->unthrottle(port);
 }
 
-static void serial8250_stop_rx(struct uart_port *port)
-{
-	struct uart_8250_port *up = up_to_u8250p(port);
-
-	serial8250_rpm_get(up);
-
-	up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
-	up->port.read_status_mask &= ~UART_LSR_DR;
-	serial_port_out(port, UART_IER, up->ier);
-
-	serial8250_rpm_put(up);
-}
-
 static void serial8250_disable_ms(struct uart_port *port)
 {
 	struct uart_8250_port *up =
-- 
2.6.3

[PATCH v5 2/3] tty: Add software emulated RS485 support for 8250

[Matwey V. Kornilov]

Implementation of software emulation of RS485 direction handling is based
on omap_serial driver.
Before and after transmission RTS is set to the appropriate value.

Note that before calling serial8250_em485_init the caller has to
ensure that UART will interrupt when shift register empty. Otherwise,
emultaion cannot be used.

Both serial8250_em485_init and serial8250_em485_destroy are
idempotent functions.

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
---
 drivers/tty/serial/8250/8250.h      |   6 ++
 drivers/tty/serial/8250/8250_port.c | 161 +++++++++++++++++++++++++++++++++++-
 include/linux/serial_8250.h         |   7 ++
 3 files changed, 170 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index d54dcd8..a3816c6 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -117,6 +117,12 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
 struct uart_8250_port *serial8250_get_port(int line);
 void serial8250_rpm_get(struct uart_8250_port *p);
 void serial8250_rpm_put(struct uart_8250_port *p);
+int serial8250_em485_init(struct uart_8250_port *p);
+void serial8250_em485_destroy(struct uart_8250_port *p);
+static inline bool serial8250_em485_enabled(struct uart_8250_port *p)
+{
+	return p->rs485_emul && (p->port.rs485.flags & SER_RS485_ENABLED);
+}
 
 #if defined(__alpha__) && !defined(CONFIG_PCI)
 /*
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 8ad0b2d..394d0d2 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -37,6 +37,7 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/pm_runtime.h>
+#include <linux/timer.h>
 
 #include <asm/io.h>
 #include <asm/irq.h>
@@ -504,6 +505,31 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
 	}
 }
 
+static inline void serial8250_em485_rts_on_send(struct uart_8250_port *p)
+{
+	unsigned char mcr = serial_in(p, UART_MCR);
+
+	if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND)
+		mcr |= UART_MCR_RTS;
+	else
+		mcr &= ~UART_MCR_RTS;
+	serial_out(p, UART_MCR, mcr);
+}
+
+static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
+{
+	unsigned char mcr = serial_in(p, UART_MCR);
+
+	if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
+		mcr |= UART_MCR_RTS;
+	else
+		mcr &= ~UART_MCR_RTS;
+	serial_out(p, UART_MCR, mcr);
+}
+
+static void serial8250_em485_handle_start_tx(unsigned long arg);
+static void serial8250_em485_handle_stop_tx(unsigned long arg);
+
 void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
 {
 	serial8250_clear_fifos(p);
@@ -528,6 +554,42 @@ void serial8250_rpm_put(struct uart_8250_port *p)
 }
 EXPORT_SYMBOL_GPL(serial8250_rpm_put);
 
+int serial8250_em485_init(struct uart_8250_port *p)
+{
+	if (p->rs485_emul != NULL)
+		return 0;
+
+	p->rs485_emul = kmalloc(sizeof(struct uart_8250_rs485_emul), GFP_KERNEL);
+	if (p->rs485_emul == NULL)
+		return -ENOMEM;
+
+	init_timer(&p->rs485_emul->stop_tx_timer);
+	p->rs485_emul->stop_tx_timer.function = serial8250_em485_handle_stop_tx;
+	p->rs485_emul->stop_tx_timer.data = (unsigned long)p;
+	p->rs485_emul->stop_tx_timer.flags |= TIMER_IRQSAFE;
+	init_timer(&p->rs485_emul->start_tx_timer);
+	p->rs485_emul->start_tx_timer.function = serial8250_em485_handle_start_tx;
+	p->rs485_emul->start_tx_timer.data = (unsigned long)p;
+	p->rs485_emul->start_tx_timer.flags |= TIMER_IRQSAFE;
+
+	serial8250_em485_rts_after_send(p);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(serial8250_em485_init);
+void serial8250_em485_destroy(struct uart_8250_port *p)
+{
+	if (p->rs485_emul == NULL)
+		return;
+
+	del_timer_sync(&p->rs485_emul->start_tx_timer);
+	del_timer_sync(&p->rs485_emul->stop_tx_timer);
+
+	kfree(p->rs485_emul);
+	p->rs485_emul = NULL;
+}
+EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
+
 /*
  * These two wrappers ensure that enable_runtime_pm_tx() can be called more than
  * once and disable_runtime_pm_tx() will still disable RPM because the fifo is
@@ -1293,7 +1355,61 @@ static void serial8250_stop_rx(struct uart_port *port)
 	serial8250_rpm_put(up);
 }
 
-static inline void __stop_tx(struct uart_8250_port *p)
+static __u32 __start_tx_rs485(struct uart_8250_port *p)
+{
+	if (!serial8250_em485_enabled(p))
+		return 0;
+
+	if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
+		serial8250_stop_rx(&p->port);
+
+	del_timer_sync(&p->rs485_emul->stop_tx_timer);
+
+	if (!!(p->port.rs485.flags & SER_RS485_RTS_ON_SEND) != !!(serial_in(p, UART_MCR) & UART_MCR_RTS)) {
+		serial8250_em485_rts_on_send(p);
+		return p->port.rs485.delay_rts_before_send;
+	}
+
+	return 0;
+}
+
+static inline void __do_stop_tx_rs485(struct uart_8250_port *p)
+{
+	if (!serial8250_em485_enabled(p))
+		return;
+
+	serial8250_em485_rts_after_send(p);
+	/*
+	* Empty the RX FIFO, we are not interested in anything
+	* received during the half-duplex transmission.
+	*/
+	if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
+		serial8250_clear_fifos(p);
+}
+
+static void serial8250_em485_handle_stop_tx(unsigned long arg)
+{
+	struct uart_8250_port *p = (struct uart_8250_port *)arg;
+
+	__do_stop_tx_rs485(p);
+}
+
+static inline void __stop_tx_rs485(struct uart_8250_port *p)
+{
+	if (!serial8250_em485_enabled(p))
+		return;
+
+	del_timer_sync(&p->rs485_emul->start_tx_timer);
+
+	/* __do_stop_tx_rs485 is going to set RTS according to config AND flush RX FIFO if required */
+	if (p->port.rs485.delay_rts_after_send > 0) {
+		mod_timer(&p->rs485_emul->stop_tx_timer, jiffies + p->port.rs485.delay_rts_after_send * HZ / 1000);
+	} else {
+		__do_stop_tx_rs485(p);
+	}
+}
+
+static inline void __do_stop_tx(struct uart_8250_port *p)
 {
 	if (p->ier & UART_IER_THRI) {
 		p->ier &= ~UART_IER_THRI;
@@ -1302,6 +1418,21 @@ static inline void __stop_tx(struct uart_8250_port *p)
 	}
 }
 
+static inline void __stop_tx(struct uart_8250_port *p)
+{
+	if (serial8250_em485_enabled(p)) {
+		unsigned char lsr = serial_in(p, UART_LSR);
+	/* To provide required timeing and allow FIFO transfer,
+	 * __stop_tx_rs485 must be called only when both FIFO and shift register
+	 * are empty. It is for device driver to enable interrupt on TEMT.
+	 */
+		if (!((lsr & UART_LSR_TEMT) && (lsr & UART_LSR_THRE)))
+			return;
+	}
+	__do_stop_tx(p);
+	__stop_tx_rs485(p);
+}
+
 static void serial8250_stop_tx(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
@@ -1319,12 +1450,10 @@ static void serial8250_stop_tx(struct uart_port *port)
 	serial8250_rpm_put(up);
 }
 
-static void serial8250_start_tx(struct uart_port *port)
+static inline void __start_tx(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 
-	serial8250_rpm_get_tx(up);
-
 	if (up->dma && !up->dma->tx_dma(up))
 		return;
 
@@ -1350,6 +1479,30 @@ static void serial8250_start_tx(struct uart_port *port)
 	}
 }
 
+static void serial8250_em485_handle_start_tx(unsigned long arg)
+{
+	struct uart_8250_port *p = (struct uart_8250_port *)arg;
+
+	__start_tx(&p->port);
+}
+
+static void serial8250_start_tx(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	__u32 delay;
+
+	serial8250_rpm_get_tx(up);
+
+	if (up->rs485_emul && timer_pending(&up->rs485_emul->start_tx_timer))
+		return;
+
+	if (up->rs485_emul && (delay = __start_tx_rs485(up))) {
+		mod_timer(&up->rs485_emul->start_tx_timer, jiffies + delay * HZ / 1000);
+	} else {
+		__start_tx(port);
+	}
+}
+
 static void serial8250_throttle(struct uart_port *port)
 {
 	port->throttle(port);
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index faa0e03..99e59fc 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -76,6 +76,11 @@ struct uart_8250_ops {
 	void		(*release_irq)(struct uart_8250_port *);
 };
 
+struct uart_8250_rs485_emul {
+	struct timer_list	start_tx_timer; /* "rs485 start tx" timer */
+	struct timer_list	stop_tx_timer; /* "rs485 stop tx" timer */
+};
+
 /*
  * This should be used by drivers which want to register
  * their own 8250 ports without registering their own
@@ -122,6 +127,8 @@ struct uart_8250_port {
 	/* 8250 specific callbacks */
 	int			(*dl_read)(struct uart_8250_port *);
 	void			(*dl_write)(struct uart_8250_port *, int);
+
+	struct uart_8250_rs485_emul *rs485_emul;
 };
 
 static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
-- 
2.6.3

[PATCH v5 3/3] tty: 8250_omap: Use software emulated RS485 direction control

[Matwey V. Kornilov]

Use software emulated RS485 direction control to provide RS485 API existed in
omap_serial driver. Note that 8250_omap issues interrupt on shift register
empty which is single prerequesite for using software emulated RS485.

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
---
 drivers/tty/serial/8250/8250_omap.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 826c5c4..323c0a4 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -698,6 +698,23 @@ static void omap_8250_throttle(struct uart_port *port)
 	pm_runtime_put_autosuspend(port->dev);
 }
 
+static int omap_8250_rs485_config(struct uart_port *port, struct serial_rs485 *rs485)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+
+	if (rs485->flags & SER_RS485_ENABLED && !serial8250_em485_enabled(up)) {
+		port->rs485 = *rs485;
+		return serial8250_em485_init(up);
+	}
+
+	if (serial8250_em485_enabled(up) && !(rs485->flags & SER_RS485_ENABLED))
+		serial8250_em485_destroy(up);
+
+	port->rs485 = *rs485;
+
+	return 0;
+}
+
 static void omap_8250_unthrottle(struct uart_port *port)
 {
 	unsigned long flags;
@@ -1144,6 +1161,7 @@ static int omap8250_probe(struct platform_device *pdev)
 	up.port.shutdown = omap_8250_shutdown;
 	up.port.throttle = omap_8250_throttle;
 	up.port.unthrottle = omap_8250_unthrottle;
+	up.port.rs485_config = omap_8250_rs485_config;
 
 	if (pdev->dev.of_node) {
 		const struct of_device_id *id;
-- 
2.6.3

Re: [PATCH v5 2/3] tty: Add software emulated RS485 support for 8250

[Andy Shevchenko]

On Sat, Dec 12, 2015 at 1:23 PM, Matwey V. Kornilov <matwey@sai.msu.ru> wrote:
> Implementation of software emulation of RS485 direction handling is based
> on omap_serial driver.
> Before and after transmission RTS is set to the appropriate value.
>
> Note that before calling serial8250_em485_init the caller has to
> ensure that UART will interrupt when shift register empty. Otherwise,
> emultaion cannot be used.
>
> Both serial8250_em485_init and serial8250_em485_destroy are
> idempotent functions.

Just nitpick suggesting to rename both struct and field:

struct uart_8250_rs485em *rs485em;

(might be 'sw' suffix as well, which I like more — rs485sw)

and corresponding local variables if any.

>
> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
> ---
>  drivers/tty/serial/8250/8250.h      |   6 ++
>  drivers/tty/serial/8250/8250_port.c | 161 +++++++++++++++++++++++++++++++++++-
>  include/linux/serial_8250.h         |   7 ++
>  3 files changed, 170 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> index d54dcd8..a3816c6 100644
> --- a/drivers/tty/serial/8250/8250.h
> +++ b/drivers/tty/serial/8250/8250.h
> @@ -117,6 +117,12 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
>  struct uart_8250_port *serial8250_get_port(int line);
>  void serial8250_rpm_get(struct uart_8250_port *p);
>  void serial8250_rpm_put(struct uart_8250_port *p);
> +int serial8250_em485_init(struct uart_8250_port *p);
> +void serial8250_em485_destroy(struct uart_8250_port *p);
> +static inline bool serial8250_em485_enabled(struct uart_8250_port *p)
> +{
> +       return p->rs485_emul && (p->port.rs485.flags & SER_RS485_ENABLED);
> +}
>
>  #if defined(__alpha__) && !defined(CONFIG_PCI)
>  /*
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 8ad0b2d..394d0d2 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -37,6 +37,7 @@
>  #include <linux/slab.h>
>  #include <linux/uaccess.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/timer.h>
>
>  #include <asm/io.h>
>  #include <asm/irq.h>
> @@ -504,6 +505,31 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
>         }
>  }
>
> +static inline void serial8250_em485_rts_on_send(struct uart_8250_port *p)
> +{
> +       unsigned char mcr = serial_in(p, UART_MCR);
> +
> +       if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND)
> +               mcr |= UART_MCR_RTS;
> +       else
> +               mcr &= ~UART_MCR_RTS;
> +       serial_out(p, UART_MCR, mcr);
> +}
> +
> +static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
> +{
> +       unsigned char mcr = serial_in(p, UART_MCR);
> +
> +       if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
> +               mcr |= UART_MCR_RTS;
> +       else
> +               mcr &= ~UART_MCR_RTS;
> +       serial_out(p, UART_MCR, mcr);
> +}
> +
> +static void serial8250_em485_handle_start_tx(unsigned long arg);
> +static void serial8250_em485_handle_stop_tx(unsigned long arg);
> +
>  void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
>  {
>         serial8250_clear_fifos(p);
> @@ -528,6 +554,42 @@ void serial8250_rpm_put(struct uart_8250_port *p)
>  }
>  EXPORT_SYMBOL_GPL(serial8250_rpm_put);
>
> +int serial8250_em485_init(struct uart_8250_port *p)
> +{
> +       if (p->rs485_emul != NULL)
> +               return 0;
> +
> +       p->rs485_emul = kmalloc(sizeof(struct uart_8250_rs485_emul), GFP_KERNEL);
> +       if (p->rs485_emul == NULL)
> +               return -ENOMEM;
> +
> +       init_timer(&p->rs485_emul->stop_tx_timer);
> +       p->rs485_emul->stop_tx_timer.function = serial8250_em485_handle_stop_tx;
> +       p->rs485_emul->stop_tx_timer.data = (unsigned long)p;
> +       p->rs485_emul->stop_tx_timer.flags |= TIMER_IRQSAFE;
> +       init_timer(&p->rs485_emul->start_tx_timer);
> +       p->rs485_emul->start_tx_timer.function = serial8250_em485_handle_start_tx;
> +       p->rs485_emul->start_tx_timer.data = (unsigned long)p;
> +       p->rs485_emul->start_tx_timer.flags |= TIMER_IRQSAFE;
> +
> +       serial8250_em485_rts_after_send(p);
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(serial8250_em485_init);
> +void serial8250_em485_destroy(struct uart_8250_port *p)
> +{
> +       if (p->rs485_emul == NULL)
> +               return;
> +
> +       del_timer_sync(&p->rs485_emul->start_tx_timer);
> +       del_timer_sync(&p->rs485_emul->stop_tx_timer);
> +
> +       kfree(p->rs485_emul);
> +       p->rs485_emul = NULL;
> +}
> +EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
> +
>  /*
>   * These two wrappers ensure that enable_runtime_pm_tx() can be called more than
>   * once and disable_runtime_pm_tx() will still disable RPM because the fifo is
> @@ -1293,7 +1355,61 @@ static void serial8250_stop_rx(struct uart_port *port)
>         serial8250_rpm_put(up);
>  }
>
> -static inline void __stop_tx(struct uart_8250_port *p)
> +static __u32 __start_tx_rs485(struct uart_8250_port *p)
> +{
> +       if (!serial8250_em485_enabled(p))
> +               return 0;
> +
> +       if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
> +               serial8250_stop_rx(&p->port);
> +
> +       del_timer_sync(&p->rs485_emul->stop_tx_timer);
> +
> +       if (!!(p->port.rs485.flags & SER_RS485_RTS_ON_SEND) != !!(serial_in(p, UART_MCR) & UART_MCR_RTS)) {
> +               serial8250_em485_rts_on_send(p);
> +               return p->port.rs485.delay_rts_before_send;
> +       }
> +
> +       return 0;
> +}
> +
> +static inline void __do_stop_tx_rs485(struct uart_8250_port *p)
> +{
> +       if (!serial8250_em485_enabled(p))
> +               return;
> +
> +       serial8250_em485_rts_after_send(p);
> +       /*
> +       * Empty the RX FIFO, we are not interested in anything
> +       * received during the half-duplex transmission.
> +       */
> +       if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
> +               serial8250_clear_fifos(p);
> +}
> +
> +static void serial8250_em485_handle_stop_tx(unsigned long arg)
> +{
> +       struct uart_8250_port *p = (struct uart_8250_port *)arg;
> +
> +       __do_stop_tx_rs485(p);
> +}
> +
> +static inline void __stop_tx_rs485(struct uart_8250_port *p)
> +{
> +       if (!serial8250_em485_enabled(p))
> +               return;
> +
> +       del_timer_sync(&p->rs485_emul->start_tx_timer);
> +
> +       /* __do_stop_tx_rs485 is going to set RTS according to config AND flush RX FIFO if required */
> +       if (p->port.rs485.delay_rts_after_send > 0) {
> +               mod_timer(&p->rs485_emul->stop_tx_timer, jiffies + p->port.rs485.delay_rts_after_send * HZ / 1000);
> +       } else {
> +               __do_stop_tx_rs485(p);
> +       }
> +}
> +
> +static inline void __do_stop_tx(struct uart_8250_port *p)
>  {
>         if (p->ier & UART_IER_THRI) {
>                 p->ier &= ~UART_IER_THRI;
> @@ -1302,6 +1418,21 @@ static inline void __stop_tx(struct uart_8250_port *p)
>         }
>  }
>
> +static inline void __stop_tx(struct uart_8250_port *p)
> +{
> +       if (serial8250_em485_enabled(p)) {
> +               unsigned char lsr = serial_in(p, UART_LSR);
> +       /* To provide required timeing and allow FIFO transfer,
> +        * __stop_tx_rs485 must be called only when both FIFO and shift register
> +        * are empty. It is for device driver to enable interrupt on TEMT.
> +        */
> +               if (!((lsr & UART_LSR_TEMT) && (lsr & UART_LSR_THRE)))
> +                       return;
> +       }
> +       __do_stop_tx(p);
> +       __stop_tx_rs485(p);
> +}
> +
>  static void serial8250_stop_tx(struct uart_port *port)
>  {
>         struct uart_8250_port *up = up_to_u8250p(port);
> @@ -1319,12 +1450,10 @@ static void serial8250_stop_tx(struct uart_port *port)
>         serial8250_rpm_put(up);
>  }
>
> -static void serial8250_start_tx(struct uart_port *port)
> +static inline void __start_tx(struct uart_port *port)
>  {
>         struct uart_8250_port *up = up_to_u8250p(port);
>
> -       serial8250_rpm_get_tx(up);
> -
>         if (up->dma && !up->dma->tx_dma(up))
>                 return;
>
> @@ -1350,6 +1479,30 @@ static void serial8250_start_tx(struct uart_port *port)
>         }
>  }
>
> +static void serial8250_em485_handle_start_tx(unsigned long arg)
> +{
> +       struct uart_8250_port *p = (struct uart_8250_port *)arg;
> +
> +       __start_tx(&p->port);
> +}
> +
> +static void serial8250_start_tx(struct uart_port *port)
> +{
> +       struct uart_8250_port *up = up_to_u8250p(port);
> +       __u32 delay;
> +
> +       serial8250_rpm_get_tx(up);
> +
> +       if (up->rs485_emul && timer_pending(&up->rs485_emul->start_tx_timer))
> +               return;
> +
> +       if (up->rs485_emul && (delay = __start_tx_rs485(up))) {
> +               mod_timer(&up->rs485_emul->start_tx_timer, jiffies + delay * HZ / 1000);
> +       } else {
> +               __start_tx(port);
> +       }
> +}
> +
>  static void serial8250_throttle(struct uart_port *port)
>  {
>         port->throttle(port);
> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
> index faa0e03..99e59fc 100644
> --- a/include/linux/serial_8250.h
> +++ b/include/linux/serial_8250.h
> @@ -76,6 +76,11 @@ struct uart_8250_ops {
>         void            (*release_irq)(struct uart_8250_port *);
>  };
>
> +struct uart_8250_rs485_emul {
> +       struct timer_list       start_tx_timer; /* "rs485 start tx" timer */
> +       struct timer_list       stop_tx_timer; /* "rs485 stop tx" timer */
> +};
> +
>  /*
>   * This should be used by drivers which want to register
>   * their own 8250 ports without registering their own
> @@ -122,6 +127,8 @@ struct uart_8250_port {
>         /* 8250 specific callbacks */
>         int                     (*dl_read)(struct uart_8250_port *);
>         void                    (*dl_write)(struct uart_8250_port *, int);
> +
> +       struct uart_8250_rs485_emul *rs485_emul;
>  };
>
>  static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
> --
> 2.6.3
>



-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v5 2/3] tty: Add software emulated RS485 support for 8250

[Matwey V. Kornilov]

2015-12-20 19:41 GMT+03:00 Andy Shevchenko <andy.shevchenko@gmail.com>:
> On Sat, Dec 12, 2015 at 1:23 PM, Matwey V. Kornilov <matwey@sai.msu.ru> wrote:
>> Implementation of software emulation of RS485 direction handling is based
>> on omap_serial driver.
>> Before and after transmission RTS is set to the appropriate value.
>>
>> Note that before calling serial8250_em485_init the caller has to
>> ensure that UART will interrupt when shift register empty. Otherwise,
>> emultaion cannot be used.
>>
>> Both serial8250_em485_init and serial8250_em485_destroy are
>> idempotent functions.
>
> Just nitpick suggesting to rename both struct and field:
>
> struct uart_8250_rs485em *rs485em;

Why not

struct uart_8250_em485 *em485;

to be consistent with function name suffix?

>
> (might be 'sw' suffix as well, which I like more — rs485sw)
>
> and corresponding local variables if any.
>
>>
>> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
>> ---
>>  drivers/tty/serial/8250/8250.h      |   6 ++
>>  drivers/tty/serial/8250/8250_port.c | 161 +++++++++++++++++++++++++++++++++++-
>>  include/linux/serial_8250.h         |   7 ++
>>  3 files changed, 170 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
>> index d54dcd8..a3816c6 100644
>> --- a/drivers/tty/serial/8250/8250.h
>> +++ b/drivers/tty/serial/8250/8250.h
>> @@ -117,6 +117,12 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
>>  struct uart_8250_port *serial8250_get_port(int line);
>>  void serial8250_rpm_get(struct uart_8250_port *p);
>>  void serial8250_rpm_put(struct uart_8250_port *p);
>> +int serial8250_em485_init(struct uart_8250_port *p);
>> +void serial8250_em485_destroy(struct uart_8250_port *p);
>> +static inline bool serial8250_em485_enabled(struct uart_8250_port *p)
>> +{
>> +       return p->rs485_emul && (p->port.rs485.flags & SER_RS485_ENABLED);
>> +}
>>
>>  #if defined(__alpha__) && !defined(CONFIG_PCI)
>>  /*
>> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
>> index 8ad0b2d..394d0d2 100644
>> --- a/drivers/tty/serial/8250/8250_port.c
>> +++ b/drivers/tty/serial/8250/8250_port.c
>> @@ -37,6 +37,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/uaccess.h>
>>  #include <linux/pm_runtime.h>
>> +#include <linux/timer.h>
>>
>>  #include <asm/io.h>
>>  #include <asm/irq.h>
>> @@ -504,6 +505,31 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
>>         }
>>  }
>>
>> +static inline void serial8250_em485_rts_on_send(struct uart_8250_port *p)
>> +{
>> +       unsigned char mcr = serial_in(p, UART_MCR);
>> +
>> +       if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND)
>> +               mcr |= UART_MCR_RTS;
>> +       else
>> +               mcr &= ~UART_MCR_RTS;
>> +       serial_out(p, UART_MCR, mcr);
>> +}
>> +
>> +static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
>> +{
>> +       unsigned char mcr = serial_in(p, UART_MCR);
>> +
>> +       if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
>> +               mcr |= UART_MCR_RTS;
>> +       else
>> +               mcr &= ~UART_MCR_RTS;
>> +       serial_out(p, UART_MCR, mcr);
>> +}
>> +
>> +static void serial8250_em485_handle_start_tx(unsigned long arg);
>> +static void serial8250_em485_handle_stop_tx(unsigned long arg);
>> +
>>  void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
>>  {
>>         serial8250_clear_fifos(p);
>> @@ -528,6 +554,42 @@ void serial8250_rpm_put(struct uart_8250_port *p)
>>  }
>>  EXPORT_SYMBOL_GPL(serial8250_rpm_put);
>>
>> +int serial8250_em485_init(struct uart_8250_port *p)
>> +{
>> +       if (p->rs485_emul != NULL)
>> +               return 0;
>> +
>> +       p->rs485_emul = kmalloc(sizeof(struct uart_8250_rs485_emul), GFP_KERNEL);
>> +       if (p->rs485_emul == NULL)
>> +               return -ENOMEM;
>> +
>> +       init_timer(&p->rs485_emul->stop_tx_timer);
>> +       p->rs485_emul->stop_tx_timer.function = serial8250_em485_handle_stop_tx;
>> +       p->rs485_emul->stop_tx_timer.data = (unsigned long)p;
>> +       p->rs485_emul->stop_tx_timer.flags |= TIMER_IRQSAFE;
>> +       init_timer(&p->rs485_emul->start_tx_timer);
>> +       p->rs485_emul->start_tx_timer.function = serial8250_em485_handle_start_tx;
>> +       p->rs485_emul->start_tx_timer.data = (unsigned long)p;
>> +       p->rs485_emul->start_tx_timer.flags |= TIMER_IRQSAFE;
>> +
>> +       serial8250_em485_rts_after_send(p);
>> +
>> +       return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(serial8250_em485_init);
>> +void serial8250_em485_destroy(struct uart_8250_port *p)
>> +{
>> +       if (p->rs485_emul == NULL)
>> +               return;
>> +
>> +       del_timer_sync(&p->rs485_emul->start_tx_timer);
>> +       del_timer_sync(&p->rs485_emul->stop_tx_timer);
>> +
>> +       kfree(p->rs485_emul);
>> +       p->rs485_emul = NULL;
>> +}
>> +EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
>> +
>>  /*
>>   * These two wrappers ensure that enable_runtime_pm_tx() can be called more than
>>   * once and disable_runtime_pm_tx() will still disable RPM because the fifo is
>> @@ -1293,7 +1355,61 @@ static void serial8250_stop_rx(struct uart_port *port)
>>         serial8250_rpm_put(up);
>>  }
>>
>> -static inline void __stop_tx(struct uart_8250_port *p)
>> +static __u32 __start_tx_rs485(struct uart_8250_port *p)
>> +{
>> +       if (!serial8250_em485_enabled(p))
>> +               return 0;
>> +
>> +       if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
>> +               serial8250_stop_rx(&p->port);
>> +
>> +       del_timer_sync(&p->rs485_emul->stop_tx_timer);
>> +
>> +       if (!!(p->port.rs485.flags & SER_RS485_RTS_ON_SEND) != !!(serial_in(p, UART_MCR) & UART_MCR_RTS)) {
>> +               serial8250_em485_rts_on_send(p);
>> +               return p->port.rs485.delay_rts_before_send;
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +static inline void __do_stop_tx_rs485(struct uart_8250_port *p)
>> +{
>> +       if (!serial8250_em485_enabled(p))
>> +               return;
>> +
>> +       serial8250_em485_rts_after_send(p);
>> +       /*
>> +       * Empty the RX FIFO, we are not interested in anything
>> +       * received during the half-duplex transmission.
>> +       */
>> +       if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
>> +               serial8250_clear_fifos(p);
>> +}
>> +
>> +static void serial8250_em485_handle_stop_tx(unsigned long arg)
>> +{
>> +       struct uart_8250_port *p = (struct uart_8250_port *)arg;
>> +
>> +       __do_stop_tx_rs485(p);
>> +}
>> +
>> +static inline void __stop_tx_rs485(struct uart_8250_port *p)
>> +{
>> +       if (!serial8250_em485_enabled(p))
>> +               return;
>> +
>> +       del_timer_sync(&p->rs485_emul->start_tx_timer);
>> +
>> +       /* __do_stop_tx_rs485 is going to set RTS according to config AND flush RX FIFO if required */
>> +       if (p->port.rs485.delay_rts_after_send > 0) {
>> +               mod_timer(&p->rs485_emul->stop_tx_timer, jiffies + p->port.rs485.delay_rts_after_send * HZ / 1000);
>> +       } else {
>> +               __do_stop_tx_rs485(p);
>> +       }
>> +}
>> +
>> +static inline void __do_stop_tx(struct uart_8250_port *p)
>>  {
>>         if (p->ier & UART_IER_THRI) {
>>                 p->ier &= ~UART_IER_THRI;
>> @@ -1302,6 +1418,21 @@ static inline void __stop_tx(struct uart_8250_port *p)
>>         }
>>  }
>>
>> +static inline void __stop_tx(struct uart_8250_port *p)
>> +{
>> +       if (serial8250_em485_enabled(p)) {
>> +               unsigned char lsr = serial_in(p, UART_LSR);
>> +       /* To provide required timeing and allow FIFO transfer,
>> +        * __stop_tx_rs485 must be called only when both FIFO and shift register
>> +        * are empty. It is for device driver to enable interrupt on TEMT.
>> +        */
>> +               if (!((lsr & UART_LSR_TEMT) && (lsr & UART_LSR_THRE)))
>> +                       return;
>> +       }
>> +       __do_stop_tx(p);
>> +       __stop_tx_rs485(p);
>> +}
>> +
>>  static void serial8250_stop_tx(struct uart_port *port)
>>  {
>>         struct uart_8250_port *up = up_to_u8250p(port);
>> @@ -1319,12 +1450,10 @@ static void serial8250_stop_tx(struct uart_port *port)
>>         serial8250_rpm_put(up);
>>  }
>>
>> -static void serial8250_start_tx(struct uart_port *port)
>> +static inline void __start_tx(struct uart_port *port)
>>  {
>>         struct uart_8250_port *up = up_to_u8250p(port);
>>
>> -       serial8250_rpm_get_tx(up);
>> -
>>         if (up->dma && !up->dma->tx_dma(up))
>>                 return;
>>
>> @@ -1350,6 +1479,30 @@ static void serial8250_start_tx(struct uart_port *port)
>>         }
>>  }
>>
>> +static void serial8250_em485_handle_start_tx(unsigned long arg)
>> +{
>> +       struct uart_8250_port *p = (struct uart_8250_port *)arg;
>> +
>> +       __start_tx(&p->port);
>> +}
>> +
>> +static void serial8250_start_tx(struct uart_port *port)
>> +{
>> +       struct uart_8250_port *up = up_to_u8250p(port);
>> +       __u32 delay;
>> +
>> +       serial8250_rpm_get_tx(up);
>> +
>> +       if (up->rs485_emul && timer_pending(&up->rs485_emul->start_tx_timer))
>> +               return;
>> +
>> +       if (up->rs485_emul && (delay = __start_tx_rs485(up))) {
>> +               mod_timer(&up->rs485_emul->start_tx_timer, jiffies + delay * HZ / 1000);
>> +       } else {
>> +               __start_tx(port);
>> +       }
>> +}
>> +
>>  static void serial8250_throttle(struct uart_port *port)
>>  {
>>         port->throttle(port);
>> diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
>> index faa0e03..99e59fc 100644
>> --- a/include/linux/serial_8250.h
>> +++ b/include/linux/serial_8250.h
>> @@ -76,6 +76,11 @@ struct uart_8250_ops {
>>         void            (*release_irq)(struct uart_8250_port *);
>>  };
>>
>> +struct uart_8250_rs485_emul {
>> +       struct timer_list       start_tx_timer; /* "rs485 start tx" timer */
>> +       struct timer_list       stop_tx_timer; /* "rs485 stop tx" timer */
>> +};
>> +
>>  /*
>>   * This should be used by drivers which want to register
>>   * their own 8250 ports without registering their own
>> @@ -122,6 +127,8 @@ struct uart_8250_port {
>>         /* 8250 specific callbacks */
>>         int                     (*dl_read)(struct uart_8250_port *);
>>         void                    (*dl_write)(struct uart_8250_port *, int);
>> +
>> +       struct uart_8250_rs485_emul *rs485_emul;
>>  };
>>
>>  static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
>> --
>> 2.6.3
>>
>
>
>
> --
> With Best Regards,
> Andy Shevchenko
>



-- 
With best regards,
Matwey V. Kornilov.
Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia
119991, Moscow, Universitetsky pr-k 13, +7 (495) 9392382

Re: [PATCH v5 2/3] tty: Add software emulated RS485 support for 8250

[Andy Shevchenko]

On Sun, Dec 20, 2015 at 8:11 PM, Matwey V. Kornilov <matwey@sai.msu.ru> wrote:
> 2015-12-20 19:41 GMT+03:00 Andy Shevchenko <andy.shevchenko@gmail.com>:
>> On Sat, Dec 12, 2015 at 1:23 PM, Matwey V. Kornilov <matwey@sai.msu.ru> wrote:
>>> Implementation of software emulation of RS485 direction handling is based
>>> on omap_serial driver.
>>> Before and after transmission RTS is set to the appropriate value.
>>>
>>> Note that before calling serial8250_em485_init the caller has to
>>> ensure that UART will interrupt when shift register empty. Otherwise,
>>> emultaion cannot be used.
>>>
>>> Both serial8250_em485_init and serial8250_em485_destroy are
>>> idempotent functions.
>>
>> Just nitpick suggesting to rename both struct and field:
>>
>> struct uart_8250_rs485em *rs485em;
>
> Why not
>
> struct uart_8250_em485 *em485;
>
> to be consistent with function name suffix?

I'm fine with that as well.

-- 
With Best Regards,
Andy Shevchenko