[PATCH v8 0/3] tty: Introduce software RS485 direction control support

[PATCH v8 0/3] tty: Introduce software RS485 direction control support

[Matwey V. Kornilov]

Changes from v7:
 - rework comments to follow guidelines
 - minor style changes
Changes from v6:
 - minor style changes
 - timers are not IRQSAFE now
Changes from v5:
 - rs485_emul variable has been renamed to em485 to follow function names convention
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

Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>

[PATCH v8 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 8d262bc..b82fcae 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1304,6 +1304,19 @@ 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) {
@@ -1371,19 +1384,6 @@ 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 =
-- 
2.7.0

[PATCH v8 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      |   2 +
 drivers/tty/serial/8250/8250_port.c | 223 +++++++++++++++++++++++++++++++++++-
 include/linux/serial_8250.h         |   8 ++
 3 files changed, 229 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index d54dcd8..ce587c0 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -117,6 +117,8 @@ 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);
 
 #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 b82fcae..c908b77 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>
@@ -522,6 +523,20 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
 	}
 }
 
+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);
@@ -546,6 +561,73 @@ void serial8250_rpm_put(struct uart_8250_port *p)
 }
 EXPORT_SYMBOL_GPL(serial8250_rpm_put);
 
+/**
+ *	serial8250_em485_init() - put uart_8250_port into rs485 emulating
+ *	@p:	uart_8250_port port instance
+ *
+ *	The function is used to start rs485 software emulating on the
+ *	&struct uart_8250_port* @p. Namely, RTS is switched before/after
+ *	transmission. The function is idempotent, so it is safe to call it
+ *	multiple times.
+ *
+ *	The caller MUST enable interrupt on empty shift register before
+ *	calling serial8250_em485_init(). This interrupt is not a part of
+ *	8250 standard, but implementation defined.
+ *
+ *	The function is supposed to be called from .rs485_config callback
+ *	or from any other callback protected with p->port.lock spinlock.
+ *
+ *	See also serial8250_em485_destroy()
+ *
+ *	Return 0 - success, -errno - otherwise
+ */
+int serial8250_em485_init(struct uart_8250_port *p)
+{
+	if (p->em485 != NULL)
+		return 0;
+
+	p->em485 = kmalloc(sizeof(struct uart_8250_em485), GFP_KERNEL);
+	if (p->em485 == NULL)
+		return -ENOMEM;
+
+	setup_timer(&p->em485->stop_tx_timer,
+		serial8250_em485_handle_stop_tx, (unsigned long)p);
+	setup_timer(&p->em485->start_tx_timer,
+		serial8250_em485_handle_start_tx, (unsigned long)p);
+	p->em485->active_timer = NULL;
+
+	serial8250_em485_rts_after_send(p);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(serial8250_em485_init);
+
+/**
+ *	serial8250_em485_destroy() - put uart_8250_port into normal state
+ *	@p:	uart_8250_port port instance
+ *
+ *	The function is used to stop rs485 software emulating on the
+ *	&struct uart_8250_port* @p. The function is idempotent, so it is safe to
+ *	call it multiple times.
+ *
+ *	The function is supposed to be called from .rs485_config callback
+ *	or from any other callback protected with p->port.lock spinlock.
+ *
+ *	See also serial8250_em485_init()
+ */
+void serial8250_em485_destroy(struct uart_8250_port *p)
+{
+	if (p->em485 == NULL)
+		return;
+
+	del_timer(&p->em485->start_tx_timer);
+	del_timer(&p->em485->stop_tx_timer);
+
+	kfree(p->em485);
+	p->em485 = 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
@@ -1317,7 +1399,56 @@ static void serial8250_stop_rx(struct uart_port *port)
 	serial8250_rpm_put(up);
 }
 
-static inline void __stop_tx(struct uart_8250_port *p)
+static void __do_stop_tx_rs485(struct uart_8250_port *p)
+{
+	if (!p->em485)
+		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;
+	struct uart_8250_em485 *em485 = p->em485;
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->port.lock, flags);
+	if (em485 &&
+	    em485->active_timer == &em485->stop_tx_timer) {
+		__do_stop_tx_rs485(p);
+		em485->active_timer = NULL;
+	}
+	spin_unlock_irqrestore(&p->port.lock, flags);
+}
+
+static void __stop_tx_rs485(struct uart_8250_port *p)
+{
+	struct uart_8250_em485 *em485 = p->em485;
+
+	if (!em485)
+		return;
+
+	/*
+	 * __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) {
+		em485->active_timer = &em485->stop_tx_timer;
+		mod_timer(&em485->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;
@@ -1326,6 +1457,28 @@ static inline void __stop_tx(struct uart_8250_port *p)
 	}
 }
 
+static inline void __stop_tx(struct uart_8250_port *p)
+{
+	struct uart_8250_em485 *em485 = p->em485;
+
+	if (em485) {
+		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 & BOTH_EMPTY) != BOTH_EMPTY)
+			return;
+
+		del_timer(&em485->start_tx_timer);
+		em485->active_timer = NULL;
+	}
+	__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);
@@ -1343,12 +1496,10 @@ 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;
 
@@ -1374,6 +1525,70 @@ static void serial8250_start_tx(struct uart_port *port)
 	}
 }
 
+static inline void start_tx_rs485(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	struct uart_8250_em485 *em485 = up->em485;
+	unsigned char mcr;
+
+	if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+		serial8250_stop_rx(&up->port);
+
+	del_timer(&em485->stop_tx_timer);
+	em485->active_timer = NULL;
+
+	mcr = serial_in(up, UART_MCR);
+	if (!!(up->port.rs485.flags & SER_RS485_RTS_ON_SEND) !=
+	    !!(mcr & UART_MCR_RTS)) {
+		if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
+			mcr |= UART_MCR_RTS;
+		else
+			mcr &= ~UART_MCR_RTS;
+		serial_out(up, UART_MCR, mcr);
+
+		if (up->port.rs485.delay_rts_before_send > 0) {
+			em485->active_timer = &em485->start_tx_timer;
+			mod_timer(&em485->start_tx_timer, jiffies +
+				up->port.rs485.delay_rts_before_send * HZ / 1000);
+			return;
+		}
+	}
+
+	__start_tx(port);
+}
+
+static void serial8250_em485_handle_start_tx(unsigned long arg)
+{
+	struct uart_8250_port *p = (struct uart_8250_port *)arg;
+	struct uart_8250_em485 *em485 = p->em485;
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->port.lock, flags);
+	if (em485 &&
+	    em485->active_timer == &em485->start_tx_timer) {
+		__start_tx(&p->port);
+		em485->active_timer = NULL;
+	}
+	spin_unlock_irqrestore(&p->port.lock, flags);
+}
+
+static void serial8250_start_tx(struct uart_port *port)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	struct uart_8250_em485 *em485 = up->em485;
+
+	serial8250_rpm_get_tx(up);
+
+	if (em485 &&
+	    em485->active_timer == &em485->start_tx_timer)
+		return;
+
+	if (em485)
+		start_tx_rs485(port);
+	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..4348797 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -76,6 +76,12 @@ struct uart_8250_ops {
 	void		(*release_irq)(struct uart_8250_port *);
 };
 
+struct uart_8250_em485 {
+	struct timer_list	start_tx_timer; /* "rs485 start tx" timer */
+	struct timer_list	stop_tx_timer;  /* "rs485 stop tx" timer */
+	struct timer_list	*active_timer;  /* pointer to active timer */
+};
+
 /*
  * This should be used by drivers which want to register
  * their own 8250 ports without registering their own
@@ -122,6 +128,8 @@ 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_em485 *em485;
 };
 
 static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
-- 
2.7.0

[PATCH v8 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 | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index a2c0734..d710985 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -697,6 +697,36 @@ 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);
+
+	/* 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);
+
+	port->rs485 = *rs485;
+
+	/*
+	 * Both serial8250_em485_init and serial8250_em485_destroy
+	 * are idempotent
+	 */
+	if (rs485->flags & SER_RS485_ENABLED) {
+		int ret = serial8250_em485_init(up);
+
+		if (ret) {
+			rs485->flags &= ~SER_RS485_ENABLED;
+			port->rs485.flags &= ~SER_RS485_ENABLED;
+		}
+		return ret;
+	}
+
+	serial8250_em485_destroy(up);
+
+	return 0;
+}
+
 static void omap_8250_unthrottle(struct uart_port *port)
 {
 	unsigned long flags;
@@ -1146,6 +1176,7 @@ 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;
-- 
2.7.0

Re: [PATCH v8 0/3] tty: Introduce software RS485 direction control support

[Peter Hurley]

Hi Matwey,

On 02/01/2016 10:09 AM, Matwey V. Kornilov wrote:
> Changes from v7:
>  - rework comments to follow guidelines
>  - minor style changes
> Changes from v6:
>  - minor style changes
>  - timers are not IRQSAFE now
> Changes from v5:
>  - rs485_emul variable has been renamed to em485 to follow function names convention
> 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
> 
> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>

The holdup here is that I'd like to unit test this, which is 3rd on my todo list.
Should be done before the end of the week which will be soon enough
for this series to make linux-next.

Thanks for your work on this.

Regards,
Peter Hurley

Re: [PATCH v8 0/3] tty: Introduce software RS485 direction control support

[Matwey V. Kornilov]

2016-02-10 19:05 GMT+03:00 Peter Hurley <peter@hurleysoftware.com>:
> Hi Matwey,
>
> On 02/01/2016 10:09 AM, Matwey V. Kornilov wrote:
>> Changes from v7:
>>  - rework comments to follow guidelines
>>  - minor style changes
>> Changes from v6:
>>  - minor style changes
>>  - timers are not IRQSAFE now
>> Changes from v5:
>>  - rs485_emul variable has been renamed to em485 to follow function names convention
>> 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
>>
>> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
>
> The holdup here is that I'd like to unit test this, which is 3rd on my todo list.
> Should be done before the end of the week which will be soon enough
> for this series to make linux-next.

Hi Peter,

Is something required from me?

>
> Thanks for your work on this.
>
> Regards,
> Peter Hurley
>



-- 
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 v8 0/3] tty: Introduce software RS485 direction control support

[Peter Hurley]

On 02/10/2016 08:24 AM, Matwey V. Kornilov wrote:
> 2016-02-10 19:05 GMT+03:00 Peter Hurley <peter@hurleysoftware.com>:
>> Hi Matwey,
>>
>> On 02/01/2016 10:09 AM, Matwey V. Kornilov wrote:
>>> Changes from v7:
>>>  - rework comments to follow guidelines
>>>  - minor style changes
>>> Changes from v6:
>>>  - minor style changes
>>>  - timers are not IRQSAFE now
>>> Changes from v5:
>>>  - rs485_emul variable has been renamed to em485 to follow function names convention
>>> 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
>>>
>>> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
>>
>> The holdup here is that I'd like to unit test this, which is 3rd on my todo list.
>> Should be done before the end of the week which will be soon enough
>> for this series to make linux-next.
> 
> Hi Peter,
> 
> Is something required from me?

Not unless my tests identify a problem. I'll let you know.