This time to lkml...
Subject: serial 8250: move push calls out of lock
Due to previous changes in the 8250 driver, the call to
tty_flip_buffer_push is now done with interrupts disabled. Not really
a huge deal, but sub-optimal.
This patch moves all of the "wake up, you have data" operations out of
the lock. This will run a little faster by avoiding dropping and
retaking the lock in the receive handler and will make the polled
serial code (which I am working on) easier to do.
>From Alan Cox:
This is actually a very good idea as it means you don't have to deal with
the problems with low_latency causing re-entry into the driver under the
lock so its conceptually much easier to follow the locking
Signed-off-by: Corey Minyard <[email protected]>
Acked-by: Alan Cox <[email protected]>
drivers/serial/8250.c | 53 +++++++++++++++++++++++++++++++-------------------
1 file changed, 33 insertions(+), 20 deletions(-)
Index: linux-2.6.21/drivers/serial/8250.c
===================================================================
--- linux-2.6.21.orig/drivers/serial/8250.c
+++ linux-2.6.21/drivers/serial/8250.c
@@ -1146,7 +1146,7 @@ static void serial8250_stop_tx(struct ua
}
}
-static void transmit_chars(struct uart_8250_port *up);
+static int transmit_chars(struct uart_8250_port *up);
static void serial8250_start_tx(struct uart_port *port)
{
@@ -1195,10 +1195,8 @@ static void serial8250_enable_ms(struct
serial_out(up, UART_IER, up->ier);
}
-static void
-receive_chars(struct uart_8250_port *up, unsigned int *status)
+static int receive_chars(struct uart_8250_port *up, unsigned int *status)
{
- struct tty_struct *tty = up->port.info->tty;
unsigned char ch, lsr = *status;
int max_count = 256;
char flag;
@@ -1262,30 +1260,30 @@ receive_chars(struct uart_8250_port *up,
ignore_char:
lsr = serial_inp(up, UART_LSR);
} while ((lsr & UART_LSR_DR) && (max_count-- > 0));
- spin_unlock(&up->port.lock);
- tty_flip_buffer_push(tty);
- spin_lock(&up->port.lock);
*status = lsr;
+
+ return 1;
}
-static void transmit_chars(struct uart_8250_port *up)
+static int transmit_chars(struct uart_8250_port *up)
{
struct circ_buf *xmit = &up->port.info->xmit;
int count;
+ int xmit_ready = 0;
if (up->port.x_char) {
serial_outp(up, UART_TX, up->port.x_char);
up->port.icount.tx++;
up->port.x_char = 0;
- return;
+ return 0;
}
if (uart_tx_stopped(&up->port)) {
serial8250_stop_tx(&up->port);
- return;
+ return 0;
}
if (uart_circ_empty(xmit)) {
__stop_tx(up);
- return;
+ return 0;
}
count = up->tx_loadsz;
@@ -1298,18 +1296,22 @@ static void transmit_chars(struct uart_8
} while (--count > 0);
if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
- uart_write_wakeup(&up->port);
+ xmit_ready = 1;
DEBUG_INTR("THRE...");
if (uart_circ_empty(xmit))
__stop_tx(up);
+
+ return xmit_ready;
}
-static unsigned int check_modem_status(struct uart_8250_port *up)
+static int check_modem_status(struct uart_8250_port *up, unsigned int *rstatus)
{
unsigned int status = serial_in(up, UART_MSR);
+ if (rstatus)
+ *rstatus = status;
if (status & UART_MSR_ANY_DELTA && up->ier & UART_IER_MSI &&
up->port.info != NULL) {
if (status & UART_MSR_TERI)
@@ -1320,11 +1322,10 @@ static unsigned int check_modem_status(s
uart_handle_dcd_change(&up->port, status & UART_MSR_DCD);
if (status & UART_MSR_DCTS)
uart_handle_cts_change(&up->port, status & UART_MSR_CTS);
-
- wake_up_interruptible(&up->port.info->delta_msr_wait);
+ return 1;
}
- return status;
+ return 0;
}
/*
@@ -1334,6 +1335,9 @@ static inline void
serial8250_handle_port(struct uart_8250_port *up)
{
unsigned int status;
+ int xmit_ready = 0;
+ int recv_ready = 0;
+ int msr_ready = 0;
unsigned long flags;
spin_lock_irqsave(&up->port.lock, flags);
@@ -1343,12 +1347,21 @@ serial8250_handle_port(struct uart_8250_
DEBUG_INTR("status = %x...", status);
if (status & UART_LSR_DR)
- receive_chars(up, &status);
- check_modem_status(up);
+ recv_ready = receive_chars(up, &status);
+ msr_ready = check_modem_status(up, NULL);
if (status & UART_LSR_THRE)
- transmit_chars(up);
+ xmit_ready = transmit_chars(up);
spin_unlock_irqrestore(&up->port.lock, flags);
+
+ if (recv_ready)
+ tty_flip_buffer_push(up->port.info->tty);
+
+ if (msr_ready)
+ wake_up_interruptible(&up->port.info->delta_msr_wait);
+
+ if (xmit_ready)
+ uart_write_wakeup(&up->port);
}
/*
@@ -1551,7 +1564,7 @@ static unsigned int serial8250_get_mctrl
unsigned int status;
unsigned int ret;
- status = check_modem_status(up);
+ check_modem_status(up, &status);
ret = 0;
if (status & UART_MSR_DCD)
-
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