linux-kernel - [PATCH 1/5] serial: sprd: Modify the baud rate calculation formula

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Message-Id: <a816deaf850b3620457ab3d071345ec572c63477.1550560916.git.baolin.wang@linaro.org>
Date:   Tue, 19 Feb 2019 15:31:11 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     gregkh@...uxfoundation.org, jslaby@...e.com, robh+dt@...nel.org,
        mark.rutland@....com, orsonzhai@...il.com, zhang.lyra@...il.com
Cc:     baolin.wang@...aro.org, broonie@...nel.org, lanqing.liu@...soc.com,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: [PATCH 1/5] serial: sprd: Modify the baud rate calculation formula

From: Lanqing Liu <lanqing.liu@...soc.com>

When the source clock is not divisible by the expected baud rate and
the remainder is not less than half of the expected baud rate, the old
formular will round up the frequency division coefficient. This will
make the actual baud rate less than the expected value and can not meet
the external transmission requirements.

Thus this patch modifies the baud rate calculation formula to support
the serial controller output the maximum baud rate.

Signed-off-by: Lanqing Liu <lanqing.liu@...soc.com>
Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
---
 drivers/tty/serial/sprd_serial.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
index 4287ca3..1891a45 100644
--- a/drivers/tty/serial/sprd_serial.c
+++ b/drivers/tty/serial/sprd_serial.c
@@ -371,7 +371,7 @@ static void sprd_set_termios(struct uart_port *port,
 	/* ask the core to calculate the divisor for us */
 	baud = uart_get_baud_rate(port, termios, old, 0, SPRD_BAUD_IO_LIMIT);
 
-	quot = (unsigned int)((port->uartclk + baud / 2) / baud);
+	quot = port->uartclk / baud;
 
 	/* set data length */
 	switch (termios->c_cflag & CSIZE) {
-- 
1.7.9.5