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 <ulrich.hecht+renesas@xxxxxxxxx>
---
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 d9f399c..553f30c 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -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)
--
2.7.4
