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Commit b96408b4 authored by Ulrich Hecht's avatar Ulrich Hecht Committed by Greg Kroah-Hartman
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serial: sh-sci: use hrtimer for receive timeout 



High latencies of classic timers cause performance issues for high-
speed serial transmissions. This patch transforms rx_timer into an
hrtimer to reduce the minimum latency.

Signed-off-by: default avatarUlrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 08fb00c6

drivers/tty/serial/sh-sci.c

+30 −17
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ 
#include <linux/init.h>

#include <linux/interrupt.h>

#include <linux/ioport.h>

#include <linux/ktime.h>

#include <linux/major.h>

#include <linux/module.h>

#include <linux/mm.h>
@@ -143,8 +144,8 @@ struct sci_port { 
	void				*rx_buf[2];

	size_t				buf_len_rx;

	struct work_struct		work_tx;

	struct timer_list		rx_timer;

	unsigned int			rx_timeout;

	struct hrtimer			rx_timer;

	unsigned int			rx_timeout;	/* microseconds */

#endif

	unsigned int			rx_frame;

	int				rx_trigger;
@@ -1229,6 +1230,15 @@ static void sci_rx_dma_release(struct sci_port *s, bool enable_pio) 
	}

}



static void start_hrtimer_us(struct hrtimer *hrt, unsigned long usec)

{

	long sec = usec / 1000000;

	long nsec = (usec % 1000000) * 1000;

	ktime_t t = ktime_set(sec, nsec);



	hrtimer_start(hrt, t, HRTIMER_MODE_REL);

}



static void sci_dma_rx_complete(void *arg)

{

	struct sci_port *s = arg;
@@ -1247,7 +1257,7 @@ static void sci_dma_rx_complete(void *arg) 
	if (active >= 0)

		count = sci_dma_rx_push(s, s->rx_buf[active], s->buf_len_rx);



	mod_timer(&s->rx_timer, jiffies + s->rx_timeout);

	start_hrtimer_us(&s->rx_timer, s->rx_timeout);



	if (count)

		tty_flip_buffer_push(&port->state->port);
@@ -1391,9 +1401,9 @@ static void work_fn_tx(struct work_struct *work) 
	dma_async_issue_pending(chan);

}



static void rx_timer_fn(struct timer_list *t)

static enum hrtimer_restart rx_timer_fn(struct hrtimer *t)

{

	struct sci_port *s = from_timer(s, t, rx_timer);

	struct sci_port *s = container_of(t, struct sci_port, rx_timer);

	struct dma_chan *chan = s->chan_rx;

	struct uart_port *port = &s->port;

	struct dma_tx_state state;
@@ -1410,7 +1420,7 @@ static void rx_timer_fn(struct timer_list *t) 
	active = sci_dma_rx_find_active(s);

	if (active < 0) {

		spin_unlock_irqrestore(&port->lock, flags);

		return;

		return HRTIMER_NORESTART;

	}



	status = dmaengine_tx_status(s->chan_rx, s->active_rx, &state);
@@ -1420,7 +1430,7 @@ static void rx_timer_fn(struct timer_list *t) 
			s->active_rx, active);



		/* Let packet complete handler take care of the packet */

		return;

		return HRTIMER_NORESTART;

	}



	dmaengine_pause(chan);
@@ -1435,7 +1445,7 @@ static void rx_timer_fn(struct timer_list *t) 
	if (status == DMA_COMPLETE) {

		spin_unlock_irqrestore(&port->lock, flags);

		dev_dbg(port->dev, "Transaction complete after DMA engine was stopped");

		return;

		return HRTIMER_NORESTART;

	}



	/* Handle incomplete DMA receive */
@@ -1460,6 +1470,8 @@ static void rx_timer_fn(struct timer_list *t) 
	serial_port_out(port, SCSCR, scr | SCSCR_RIE);



	spin_unlock_irqrestore(&port->lock, flags);



	return HRTIMER_NORESTART;

}



static struct dma_chan *sci_request_dma_chan(struct uart_port *port,
@@ -1571,7 +1583,8 @@ static void sci_request_dma(struct uart_port *port) 
			dma += s->buf_len_rx;

		}



		timer_setup(&s->rx_timer, rx_timer_fn, 0);

		hrtimer_init(&s->rx_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

		s->rx_timer.function = rx_timer_fn;



		if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)

			sci_submit_rx(s);
@@ -1630,9 +1643,9 @@ static irqreturn_t sci_rx_interrupt(int irq, void *ptr) 
		/* Clear current interrupt */

		serial_port_out(port, SCxSR,

				ssr & ~(SCIF_DR | SCxSR_RDxF(port)));

		dev_dbg(port->dev, "Rx IRQ %lu: setup t-out in %u jiffies\n",

		dev_dbg(port->dev, "Rx IRQ %lu: setup t-out in %u us\n",

			jiffies, s->rx_timeout);

		mod_timer(&s->rx_timer, jiffies + s->rx_timeout);

		start_hrtimer_us(&s->rx_timer, s->rx_timeout);



		return IRQ_HANDLED;

	}
@@ -1643,7 +1656,7 @@ static irqreturn_t sci_rx_interrupt(int irq, void *ptr) 
			scif_set_rtrg(port, s->rx_trigger);



		mod_timer(&s->rx_fifo_timer, jiffies + DIV_ROUND_UP(

			  s->rx_frame * s->rx_fifo_timeout, 1000));

			  s->rx_frame * HZ * s->rx_fifo_timeout, 1000000));

	}



	/* I think sci_receive_chars has to be called irrespective
@@ -2079,7 +2092,7 @@ static void sci_shutdown(struct uart_port *port) 
	if (s->chan_rx) {

		dev_dbg(port->dev, "%s(%d) deleting rx_timer\n", __func__,

			port->line);

		del_timer_sync(&s->rx_timer);

		hrtimer_cancel(&s->rx_timer);

	}

#endif
@@ -2480,11 +2493,11 @@ static void sci_set_termios(struct uart_port *port, struct ktermios *termios, 
	if (termios->c_cflag & PARENB)

		bits++;



	s->rx_frame = (100 * bits * HZ) / (baud / 10);

	s->rx_frame = (10000 * bits) / (baud / 100);

#ifdef CONFIG_SERIAL_SH_SCI_DMA

	s->rx_timeout = DIV_ROUND_UP(s->buf_len_rx * 2 * s->rx_frame, 1000);

	if (s->rx_timeout < msecs_to_jiffies(20))

		s->rx_timeout = msecs_to_jiffies(20);

	s->rx_timeout = s->buf_len_rx * 2 * s->rx_frame;

	if (s->rx_timeout < 20)

		s->rx_timeout = 20;

#endif



	if ((termios->c_cflag & CREAD) != 0)