linux-kernel - [BACKPORT 4.14.y v2 6/6] serial: sprd: Modify the baud rate calculation formula

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Message-Id: <4fe6ec82960301126b9f4be52dd6083c30e17420.1567649729.git.baolin.wang@linaro.org>
Date:   Thu,  5 Sep 2019 11:11:26 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     stable@...r.kernel.org, gregkh@...uxfoundation.org
Cc:     lanqing.liu@...soc.com, linux-serial@...r.kernel.org,
        arnd@...db.de, baolin.wang@...aro.org, orsonzhai@...il.com,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org
Subject: [BACKPORT 4.14.y v2 6/6] serial: sprd: Modify the baud rate calculation formula

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

[Upstream commit 5b9cea15a3de5d65000d49f626b71b00d42a0577]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 e902494..72e96ab8 100644
--- a/drivers/tty/serial/sprd_serial.c
+++ b/drivers/tty/serial/sprd_serial.c
@@ -380,7 +380,7 @@ 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