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From: Baolin Wang <baolin.wang@linaro.org>
To: stable@vger.kernel.org, gregkh@linuxfoundation.org
Cc: lanqing.liu@unisoc.com, linux-serial@vger.kernel.org,
	arnd@arndb.de, baolin.wang@linaro.org, orsonzhai@gmail.com,
	vincent.guittot@linaro.org, linux-kernel@vger.kernel.org
Subject: [BACKPORT 4.14.y v2 6/6] serial: sprd: Modify the baud rate calculation formula
Date: Thu,  5 Sep 2019 11:11:26 +0800	[thread overview]
Message-ID: <4fe6ec82960301126b9f4be52dd6083c30e17420.1567649729.git.baolin.wang@linaro.org> (raw)
In-Reply-To: <cover.1567649728.git.baolin.wang@linaro.org>

From: Lanqing Liu <lanqing.liu@unisoc.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@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Baolin Wang <baolin.wang@linaro.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


  parent reply	other threads:[~2019-09-05  3:12 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-05  3:05 [BACKPORT 4.14.y v2 0/6] Candidates from Spreadtrum 4.14 product kernel Baolin Wang
2019-09-05  3:06 ` [BACKPORT 4.14.y v2 1/6] ip6: fix skb leak in ip6frag_expire_frag_queue() Baolin Wang
2019-09-05  3:07 ` [BACKPORT 4.14.y v2 2/6] locking/lockdep: Add debug_locks check in __lock_downgrade() Baolin Wang
2019-09-10 14:32   ` Greg KH
2019-09-11  3:39     ` Baolin Wang
2019-09-05  3:07 ` [BACKPORT 4.14.y v2 3/6] pinctrl: sprd: Use define directive for sprd_pinconf_params values Baolin Wang
2019-09-05  3:08 ` [BACKPORT 4.14.y v2 4/6] power: supply: sysfs: ratelimit property read error message Baolin Wang
2019-09-05  3:10 ` [BACKPORT 4.14.y v2 5/6] ppp: mppe: Revert "ppp: mppe: Add softdep to arc4" Baolin Wang
2019-09-05 16:16   ` Eric Biggers
2019-09-06  6:13     ` Baolin Wang
2019-09-05  3:11 ` Baolin Wang [this message]
2019-09-05  9:01   ` [BACKPORT 4.14.y v2 6/6] serial: sprd: Modify the baud rate calculation formula Johan Hovold
2019-09-05  9:58     ` Baolin Wang
2019-09-20  8:06       ` Johan Hovold

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