tty: Add software emulated RS485 support for 8250
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
Greg Kroah-Hartman
parent
a07a70bcb7
commit
e490c9144c
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@ -117,6 +117,8 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
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struct uart_8250_port *serial8250_get_port(int line);
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void serial8250_rpm_get(struct uart_8250_port *p);
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void serial8250_rpm_put(struct uart_8250_port *p);
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int serial8250_em485_init(struct uart_8250_port *p);
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void serial8250_em485_destroy(struct uart_8250_port *p);
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#if defined(__alpha__) && !defined(CONFIG_PCI)
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/*
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@ -37,6 +37,7 @@
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#include <linux/slab.h>
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#include <linux/uaccess.h>
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#include <linux/pm_runtime.h>
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#include <linux/timer.h>
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#include <asm/io.h>
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#include <asm/irq.h>
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@ -522,6 +523,20 @@ static void serial8250_clear_fifos(struct uart_8250_port *p)
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}
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}
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static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
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{
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unsigned char mcr = serial_in(p, UART_MCR);
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if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
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mcr |= UART_MCR_RTS;
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else
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mcr &= ~UART_MCR_RTS;
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serial_out(p, UART_MCR, mcr);
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}
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static void serial8250_em485_handle_start_tx(unsigned long arg);
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static void serial8250_em485_handle_stop_tx(unsigned long arg);
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void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
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{
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serial8250_clear_fifos(p);
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@ -546,6 +561,73 @@ void serial8250_rpm_put(struct uart_8250_port *p)
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}
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EXPORT_SYMBOL_GPL(serial8250_rpm_put);
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/**
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* serial8250_em485_init() - put uart_8250_port into rs485 emulating
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* @p: uart_8250_port port instance
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*
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* The function is used to start rs485 software emulating on the
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* &struct uart_8250_port* @p. Namely, RTS is switched before/after
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* transmission. The function is idempotent, so it is safe to call it
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* multiple times.
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*
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* The caller MUST enable interrupt on empty shift register before
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* calling serial8250_em485_init(). This interrupt is not a part of
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* 8250 standard, but implementation defined.
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*
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* The function is supposed to be called from .rs485_config callback
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* or from any other callback protected with p->port.lock spinlock.
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*
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* See also serial8250_em485_destroy()
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*
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* Return 0 - success, -errno - otherwise
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*/
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int serial8250_em485_init(struct uart_8250_port *p)
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{
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if (p->em485 != NULL)
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return 0;
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p->em485 = kmalloc(sizeof(struct uart_8250_em485), GFP_KERNEL);
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if (p->em485 == NULL)
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return -ENOMEM;
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setup_timer(&p->em485->stop_tx_timer,
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serial8250_em485_handle_stop_tx, (unsigned long)p);
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setup_timer(&p->em485->start_tx_timer,
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serial8250_em485_handle_start_tx, (unsigned long)p);
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p->em485->active_timer = NULL;
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serial8250_em485_rts_after_send(p);
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return 0;
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}
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EXPORT_SYMBOL_GPL(serial8250_em485_init);
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/**
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* serial8250_em485_destroy() - put uart_8250_port into normal state
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* @p: uart_8250_port port instance
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*
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* The function is used to stop rs485 software emulating on the
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* &struct uart_8250_port* @p. The function is idempotent, so it is safe to
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* call it multiple times.
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*
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* The function is supposed to be called from .rs485_config callback
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* or from any other callback protected with p->port.lock spinlock.
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*
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* See also serial8250_em485_init()
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*/
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void serial8250_em485_destroy(struct uart_8250_port *p)
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{
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if (p->em485 == NULL)
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return;
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del_timer(&p->em485->start_tx_timer);
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del_timer(&p->em485->stop_tx_timer);
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kfree(p->em485);
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p->em485 = NULL;
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}
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EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
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/*
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* These two wrappers ensure that enable_runtime_pm_tx() can be called more than
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* once and disable_runtime_pm_tx() will still disable RPM because the fifo is
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@ -1317,7 +1399,56 @@ static void serial8250_stop_rx(struct uart_port *port)
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serial8250_rpm_put(up);
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}
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static inline void __stop_tx(struct uart_8250_port *p)
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static void __do_stop_tx_rs485(struct uart_8250_port *p)
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{
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if (!p->em485)
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return;
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serial8250_em485_rts_after_send(p);
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/*
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* Empty the RX FIFO, we are not interested in anything
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* received during the half-duplex transmission.
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*/
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if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
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serial8250_clear_fifos(p);
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}
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static void serial8250_em485_handle_stop_tx(unsigned long arg)
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{
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struct uart_8250_port *p = (struct uart_8250_port *)arg;
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struct uart_8250_em485 *em485 = p->em485;
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unsigned long flags;
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spin_lock_irqsave(&p->port.lock, flags);
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if (em485 &&
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em485->active_timer == &em485->stop_tx_timer) {
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__do_stop_tx_rs485(p);
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em485->active_timer = NULL;
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}
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spin_unlock_irqrestore(&p->port.lock, flags);
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}
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static void __stop_tx_rs485(struct uart_8250_port *p)
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{
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struct uart_8250_em485 *em485 = p->em485;
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if (!em485)
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return;
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/*
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* __do_stop_tx_rs485 is going to set RTS according to config
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* AND flush RX FIFO if required.
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*/
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if (p->port.rs485.delay_rts_after_send > 0) {
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em485->active_timer = &em485->stop_tx_timer;
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mod_timer(&em485->stop_tx_timer, jiffies +
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p->port.rs485.delay_rts_after_send * HZ / 1000);
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} else {
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__do_stop_tx_rs485(p);
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}
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}
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static inline void __do_stop_tx(struct uart_8250_port *p)
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{
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if (p->ier & UART_IER_THRI) {
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p->ier &= ~UART_IER_THRI;
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@ -1326,6 +1457,28 @@ static inline void __stop_tx(struct uart_8250_port *p)
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}
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}
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static inline void __stop_tx(struct uart_8250_port *p)
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{
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struct uart_8250_em485 *em485 = p->em485;
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if (em485) {
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unsigned char lsr = serial_in(p, UART_LSR);
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/*
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* To provide required timeing and allow FIFO transfer,
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* __stop_tx_rs485 must be called only when both FIFO and
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* shift register are empty. It is for device driver to enable
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* interrupt on TEMT.
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*/
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if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
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return;
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del_timer(&em485->start_tx_timer);
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em485->active_timer = NULL;
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}
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__do_stop_tx(p);
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__stop_tx_rs485(p);
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}
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static void serial8250_stop_tx(struct uart_port *port)
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{
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struct uart_8250_port *up = up_to_u8250p(port);
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@ -1343,12 +1496,10 @@ static void serial8250_stop_tx(struct uart_port *port)
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serial8250_rpm_put(up);
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}
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static void serial8250_start_tx(struct uart_port *port)
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static inline void __start_tx(struct uart_port *port)
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{
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struct uart_8250_port *up = up_to_u8250p(port);
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serial8250_rpm_get_tx(up);
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if (up->dma && !up->dma->tx_dma(up))
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return;
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@ -1374,6 +1525,70 @@ static void serial8250_start_tx(struct uart_port *port)
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}
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}
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static inline void start_tx_rs485(struct uart_port *port)
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{
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struct uart_8250_port *up = up_to_u8250p(port);
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struct uart_8250_em485 *em485 = up->em485;
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unsigned char mcr;
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if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
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serial8250_stop_rx(&up->port);
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del_timer(&em485->stop_tx_timer);
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em485->active_timer = NULL;
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mcr = serial_in(up, UART_MCR);
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if (!!(up->port.rs485.flags & SER_RS485_RTS_ON_SEND) !=
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!!(mcr & UART_MCR_RTS)) {
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if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
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mcr |= UART_MCR_RTS;
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else
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mcr &= ~UART_MCR_RTS;
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serial_out(up, UART_MCR, mcr);
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if (up->port.rs485.delay_rts_before_send > 0) {
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em485->active_timer = &em485->start_tx_timer;
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mod_timer(&em485->start_tx_timer, jiffies +
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up->port.rs485.delay_rts_before_send * HZ / 1000);
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return;
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}
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}
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__start_tx(port);
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}
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static void serial8250_em485_handle_start_tx(unsigned long arg)
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{
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struct uart_8250_port *p = (struct uart_8250_port *)arg;
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struct uart_8250_em485 *em485 = p->em485;
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unsigned long flags;
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spin_lock_irqsave(&p->port.lock, flags);
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if (em485 &&
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em485->active_timer == &em485->start_tx_timer) {
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__start_tx(&p->port);
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em485->active_timer = NULL;
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}
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spin_unlock_irqrestore(&p->port.lock, flags);
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}
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static void serial8250_start_tx(struct uart_port *port)
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{
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struct uart_8250_port *up = up_to_u8250p(port);
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struct uart_8250_em485 *em485 = up->em485;
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serial8250_rpm_get_tx(up);
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if (em485 &&
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em485->active_timer == &em485->start_tx_timer)
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return;
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if (em485)
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start_tx_rs485(port);
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else
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__start_tx(port);
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}
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static void serial8250_throttle(struct uart_port *port)
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{
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port->throttle(port);
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@ -76,6 +76,12 @@ struct uart_8250_ops {
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void (*release_irq)(struct uart_8250_port *);
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};
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struct uart_8250_em485 {
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struct timer_list start_tx_timer; /* "rs485 start tx" timer */
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struct timer_list stop_tx_timer; /* "rs485 stop tx" timer */
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struct timer_list *active_timer; /* pointer to active timer */
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};
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/*
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* This should be used by drivers which want to register
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* their own 8250 ports without registering their own
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@ -122,6 +128,8 @@ struct uart_8250_port {
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/* 8250 specific callbacks */
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int (*dl_read)(struct uart_8250_port *);
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void (*dl_write)(struct uart_8250_port *, int);
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struct uart_8250_em485 *em485;
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};
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static inline struct uart_8250_port *up_to_u8250p(struct uart_port *up)
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