From b96408b47480f9947eee933fcce35ed4ae74cc9a Mon Sep 17 00:00:00 2001 From: Ulrich Hecht Date: Thu, 15 Feb 2018 13:02:41 +0100 Subject: [PATCH] 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: Ulrich Hecht Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/sh-sci.c | 47 +++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 17 deletions(-) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 7257c078e155..af1c3246cee1 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -33,6 +33,7 @@ #include #include #include +#include #include #include #include @@ -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 @@ done: 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) -- 2.11.0