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tty: Add software emulated RS485 support for 8250

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Matwey V. Kornilov 2016-02-01 21:09:21 +03:00 committed by Greg Kroah-Hartman
parent a07a70bcb7
commit e490c9144c
3 changed files with 229 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/tty/serial/8250/8250.h
View File

@ -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)
/*

223
drivers/tty/serial/8250/8250_port.c
View File

@ -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);

8
include/linux/serial_8250.h
View File

@ -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)