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serial: 8250: Use hrtimers for rs485 delays
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Previously the timers where based on the classic timers, giving a too
coarse resolution on systems with configs of less than 1000 HZ.

This patch changes the rs485 timers to hrtimers.

Signed-off-by: Rafael Gago Castano <rgc@hms.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Rafael Gago authored and Greg Kroah-Hartman committed Aug 28, 2017
1 parent a6845e1 commit 6e0a5de
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Showing 2 changed files with 44 additions and 26 deletions.
63 changes: 40 additions & 23 deletions drivers/tty/serial/8250/8250_port.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,7 @@
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/pm_runtime.h>
#include <linux/timer.h>
#include <linux/ktime.h>

#include <asm/io.h>
#include <asm/irq.h>
Expand Down Expand Up @@ -553,8 +553,8 @@ static inline void serial8250_em485_rts_after_send(struct uart_8250_port *p)
serial8250_out_MCR(p, mcr);
}

static void serial8250_em485_handle_start_tx(unsigned long arg);
static void serial8250_em485_handle_stop_tx(unsigned long arg);
static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t);
static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t);

void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p)
{
Expand Down Expand Up @@ -609,12 +609,14 @@ int serial8250_em485_init(struct uart_8250_port *p)
if (!p->em485)
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);
hrtimer_init(&p->em485->stop_tx_timer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
hrtimer_init(&p->em485->start_tx_timer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
p->em485->stop_tx_timer.function = &serial8250_em485_handle_stop_tx;
p->em485->start_tx_timer.function = &serial8250_em485_handle_start_tx;
p->em485->port = p;
p->em485->active_timer = NULL;

serial8250_em485_rts_after_send(p);

return 0;
Expand All @@ -639,8 +641,8 @@ void serial8250_em485_destroy(struct uart_8250_port *p)
if (!p->em485)
return;

del_timer(&p->em485->start_tx_timer);
del_timer(&p->em485->stop_tx_timer);
hrtimer_cancel(&p->em485->start_tx_timer);
hrtimer_cancel(&p->em485->stop_tx_timer);

kfree(p->em485);
p->em485 = NULL;
Expand Down Expand Up @@ -1435,12 +1437,13 @@ static void __do_stop_tx_rs485(struct uart_8250_port *p)
serial_port_out(&p->port, UART_IER, p->ier);
}
}

static void serial8250_em485_handle_stop_tx(unsigned long arg)
static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t)
{
struct uart_8250_port *p = (struct uart_8250_port *)arg;
struct uart_8250_em485 *em485 = p->em485;
struct uart_8250_em485 *em485;
struct uart_8250_port *p;
unsigned long flags;
em485 = container_of(t, struct uart_8250_em485, stop_tx_timer);
p = em485->port;

serial8250_rpm_get(p);
spin_lock_irqsave(&p->port.lock, flags);
Expand All @@ -1451,6 +1454,16 @@ static void serial8250_em485_handle_stop_tx(unsigned long arg)
}
spin_unlock_irqrestore(&p->port.lock, flags);
serial8250_rpm_put(p);
return HRTIMER_NORESTART;
}

static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
{
long sec = msec / 1000;
long nsec = (msec % 1000) * 1000000;
ktime_t t = ktime_set(sec, nsec);

hrtimer_start(hrt, t, HRTIMER_MODE_REL);
}

static void __stop_tx_rs485(struct uart_8250_port *p)
Expand All @@ -1463,8 +1476,8 @@ 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;
mod_timer(&em485->stop_tx_timer, jiffies +
p->port.rs485.delay_rts_after_send * HZ / 1000);
start_hrtimer_ms(&em485->stop_tx_timer,
p->port.rs485.delay_rts_after_send);
} else {
__do_stop_tx_rs485(p);
}
Expand Down Expand Up @@ -1494,8 +1507,8 @@ static inline void __stop_tx(struct uart_8250_port *p)
if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
return;

del_timer(&em485->start_tx_timer);
em485->active_timer = NULL;
hrtimer_cancel(&em485->start_tx_timer);

__stop_tx_rs485(p);
}
Expand Down Expand Up @@ -1558,8 +1571,9 @@ static inline void start_tx_rs485(struct uart_port *port)
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;
if (hrtimer_is_queued(&em485->stop_tx_timer))
hrtimer_cancel(&em485->stop_tx_timer);

mcr = serial8250_in_MCR(up);
if (!!(up->port.rs485.flags & SER_RS485_RTS_ON_SEND) !=
Expand All @@ -1572,20 +1586,22 @@ 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;
mod_timer(&em485->start_tx_timer, jiffies +
up->port.rs485.delay_rts_before_send * HZ / 1000);
start_hrtimer_ms(&em485->start_tx_timer,
up->port.rs485.delay_rts_before_send);
return;
}
}

__start_tx(port);
}

static void serial8250_em485_handle_start_tx(unsigned long arg)
static enum hrtimer_restart serial8250_em485_handle_start_tx(struct hrtimer *t)
{
struct uart_8250_port *p = (struct uart_8250_port *)arg;
struct uart_8250_em485 *em485 = p->em485;
struct uart_8250_em485 *em485;
struct uart_8250_port *p;
unsigned long flags;
em485 = container_of(t, struct uart_8250_em485, start_tx_timer);
p = em485->port;

spin_lock_irqsave(&p->port.lock, flags);
if (em485 &&
Expand All @@ -1594,6 +1610,7 @@ static void serial8250_em485_handle_start_tx(unsigned long arg)
em485->active_timer = NULL;
}
spin_unlock_irqrestore(&p->port.lock, flags);
return HRTIMER_NORESTART;
}

static void serial8250_start_tx(struct uart_port *port)
Expand Down
7 changes: 4 additions & 3 deletions include/linux/serial_8250.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -80,9 +80,10 @@ struct uart_8250_ops {
};

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 */
struct hrtimer start_tx_timer; /* "rs485 start tx" timer */
struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */
struct hrtimer *active_timer; /* pointer to active timer */
struct uart_8250_port *port; /* for hrtimer callbacks */
};

/*
Expand Down

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