[PATCH v4 2/2] serial: mxc: Speed-up character transmission

[Loic Poulain]

Instead of waiting for empty FIFO condition before writing a
character, wait for non-full FIFO condition.

This helps in saving several tens of milliseconds during boot
(depending verbosity).

Signed-off-by: Loic Poulain <loic.poulain at linaro.org>
Tested-by: Lothar Waßmann <LW at KARO-electronics.de>
Acked-by: Pali Rohár <pali at kernel.org>
---
 v2: fixing transfert abort & char corruption commit
 v3: Reordering commits for good bisectability
 v4: no code change

 drivers/serial/serial_mxc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
index 9e5b987994..cac1922354 100644
--- a/drivers/serial/serial_mxc.c
+++ b/drivers/serial/serial_mxc.c
@@ -240,11 +240,11 @@ static void mxc_serial_putc(const char c)
 	if (c == '\n')
 		serial_putc('\r');
 
-	writel(c, &mxc_base->txd);
-
 	/* wait for transmitter to be ready */
-	while (!(readl(&mxc_base->ts) & UTS_TXEMPTY))
+	while (readl(&mxc_base->ts) & UTS_TXFULL)
 		schedule();
+
+	writel(c, &mxc_base->txd);
 }
 
 /* Test whether a character is in the RX buffer */
@@ -335,7 +335,7 @@ static int mxc_serial_putc(struct udevice *dev, const char ch)
 	struct mxc_serial_plat *plat = dev_get_plat(dev);
 	struct mxc_uart *const uart = plat->reg;
 
-	if (!(readl(&uart->ts) & UTS_TXEMPTY))
+	if (readl(&uart->ts) & UTS_TXFULL)
 		return -EAGAIN;
 
 	writel(ch, &uart->txd);
-- 
2.34.1