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From:   Yu Tu <yu.tu@amlogic.com>
To:     <linux-serial@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-amlogic@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Kevin Hilman <khilman@baylibre.com>,
        Jerome Brunet <jbrunet@baylibre.com>
CC:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
        Yu Tu <yu.tu@amlogic.com>
Subject: [PATCH 1/3] tty: serial: meson: Use DIV_ROUND_CLOSEST to calculate baud rates
Date:   Thu, 7 Apr 2022 16:13:53 +0800
Message-ID: <20220407081355.13602-2-yu.tu@amlogic.com>
In-Reply-To: <20220407081355.13602-1-yu.tu@amlogic.com>
References: <20220407081355.13602-1-yu.tu@amlogic.com>
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Due to chip process differences, chip designers recommend using baud
rates as close to and larger as possible in order to reduce clock
errors.

Signed-off-by: Yu Tu <yu.tu@amlogic.com>
---
 drivers/tty/serial/meson_uart.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 2bf1c57e0981..8e59624935af 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -299,10 +299,10 @@ static void meson_uart_change_speed(struct uart_port *port, unsigned long baud)
 		cpu_relax();
 
 	if (port->uartclk == 24000000) {
-		val = ((port->uartclk / 3) / baud) - 1;
+		val = DIV_ROUND_CLOSEST(port->uartclk / 3, baud) - 1;
 		val |= AML_UART_BAUD_XTAL;
 	} else {
-		val = ((port->uartclk * 10 / (baud * 4) + 5) / 10) - 1;
+		val =  DIV_ROUND_CLOSEST(port->uartclk / 4, baud) - 1;
 	}
 	val |= AML_UART_BAUD_USE;
 	writel(val, port->membase + AML_UART_REG5);
-- 
2.33.1