From: Loic Poulain <loic.poulain@linaro.org>
Date: Thu, 12 Jan 2023 17:19:51 +0000 (+0100)
Subject: serial: mxc: Speed-up character transmission
X-Git-Tag: baikal/mips/sdk5.8.2~5^2~65^2~46
X-Git-Url: https://git.baikalelectronics.ru/?a=commitdiff_plain;h=2377be405195577eccb901df33636a6d9b3245c7;p=uboot.git

serial: mxc: Speed-up character transmission

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@linaro.org>
Tested-by: Lothar Waßmann <LW@KARO-electronics.de>
Acked-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Tested-by: Fabio Estevam <festevam@denx.de>
---

diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
index e4ffa9c3f6..cc85a50272 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);