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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
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+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)