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Subject[PATCH 10/25] serial: bfin_sport_uart: only enable SPORT TX if data is to be sent
Date
From: Sonic Zhang <sonic.zhang@analog.com>

Rather than always turn on the SPORT TX interrupt, only do it when we've
actually queued up data for transmission. This avoids useless interrupt
processing.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
drivers/serial/bfin_sport_uart.c | 30 +++++++++++++++++++++---------
1 files changed, 21 insertions(+), 9 deletions(-)
diff --git a/drivers/serial/bfin_sport_uart.c b/drivers/serial/bfin_sport_uart.c
index b9938ac..0b459cf 100644
--- a/drivers/serial/bfin_sport_uart.c
+++ b/drivers/serial/bfin_sport_uart.c
@@ -54,7 +54,7 @@ struct sport_uart_port {
#endif
};

-static void sport_uart_tx_chars(struct sport_uart_port *up);
+static int sport_uart_tx_chars(struct sport_uart_port *up);
static void sport_stop_tx(struct uart_port *port);

static inline void tx_one_byte(struct sport_uart_port *up, unsigned int value)
@@ -307,18 +307,24 @@ static int sport_startup(struct uart_port *port)
return ret;
}

-static void sport_uart_tx_chars(struct sport_uart_port *up)
+/*
+ * sport_uart_tx_chars
+ *
+ * ret 1 means need to enable sport.
+ * ret 0 means do nothing.
+ */
+static int sport_uart_tx_chars(struct sport_uart_port *up)
{
struct circ_buf *xmit = &up->port.state->xmit;

if (SPORT_GET_STAT(up) & TXF)
- return;
+ return 0;

if (up->port.x_char) {
tx_one_byte(up, up->port.x_char);
up->port.icount.tx++;
up->port.x_char = 0;
- return;
+ return 1;
}

if (uart_circ_empty(xmit) || uart_tx_stopped(&up->port)) {
@@ -329,7 +335,7 @@ static void sport_uart_tx_chars(struct sport_uart_port *up)
*/
if (SPORT_GET_STAT(up) & TXHRE)
sport_stop_tx(&up->port);
- return;
+ return 0;
}

while(!(SPORT_GET_STAT(up) & TXF) && !uart_circ_empty(xmit)) {
@@ -340,6 +346,8 @@ static void sport_uart_tx_chars(struct sport_uart_port *up)

if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
uart_write_wakeup(&up->port);
+
+ return 1;
}

static unsigned int sport_tx_empty(struct uart_port *port)
@@ -361,6 +369,9 @@ static void sport_stop_tx(struct uart_port *port)

pr_debug("%s enter\n", __func__);

+ if (!(SPORT_GET_TCR1(up) & TSPEN))
+ return;
+
/* Although the hold register is empty, last byte is still in shift
* register and not sent out yet. So, put a dummy data into TX FIFO.
* Then, sport tx stops when last byte is shift out and the dummy
@@ -383,11 +394,12 @@ static void sport_start_tx(struct uart_port *port)
pr_debug("%s enter\n", __func__);

/* Write data into SPORT FIFO before enable SPROT to transmit */
- sport_uart_tx_chars(up);
+ if (sport_uart_tx_chars(up)) {
+ /* Enable transmit, then an interrupt will generated */
+ SPORT_PUT_TCR1(up, (SPORT_GET_TCR1(up) | TSPEN));
+ SSYNC();
+ }

- /* Enable transmit, then an interrupt will generated */
- SPORT_PUT_TCR1(up, (SPORT_GET_TCR1(up) | TSPEN));
- SSYNC();
pr_debug("%s exit\n", __func__);
}

--
1.7.0.3


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