linux-kernel - [PATCH] Uartlite: speed up console output

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Date:	Sun, 21 Oct 2007 17:02:55 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	jacmet@...site.dk
Subject: [PATCH] Uartlite: speed up console output

From: Grant Likely <grant.likely@...retlab.ca>

Change the wait_tx routine to call cpu_relax() instead of udelay() to
reduce console output latency and test for the TXFULL bit instead of
TXEMPTY.  That way the FIFO doesn't need to by 100% flushed before
writing the next character.

Signed-off-by: Grant Likely <grant.likely@...retlab.ca>
---

 drivers/serial/uartlite.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/serial/uartlite.c b/drivers/serial/uartlite.c
index dfef83f..a85f2d3 100644
--- a/drivers/serial/uartlite.c
+++ b/drivers/serial/uartlite.c
@@ -329,12 +329,14 @@ static struct uart_ops ulite_ops = {
 static void ulite_console_wait_tx(struct uart_port *port)
 {
 	int i;
+	u8 val;
 
-	/* wait up to 10ms for the character(s) to be sent */
-	for (i = 0; i < 10000; i++) {
-		if (readb(port->membase + ULITE_STATUS) & ULITE_STATUS_TXEMPTY)
+	/* Spin waiting for TX fifo to have space available */
+	for (i = 0; i < 100000; i++) {
+		val = readb(port->membase + ULITE_STATUS);
+		if ((val & ULITE_STATUS_TXFULL) == 0)
 			break;
-		udelay(1);
+		cpu_relax();
 	}
 }
 

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