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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	[thread overview]
Message-ID: <20220407081355.13602-2-yu.tu@amlogic.com> (raw)
In-Reply-To: <20220407081355.13602-1-yu.tu@amlogic.com>

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


WARNING: multiple messages have this Message-ID (diff)
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	[thread overview]
Message-ID: <20220407081355.13602-2-yu.tu@amlogic.com> (raw)
In-Reply-To: <20220407081355.13602-1-yu.tu@amlogic.com>

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


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
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	[thread overview]
Message-ID: <20220407081355.13602-2-yu.tu@amlogic.com> (raw)
In-Reply-To: <20220407081355.13602-1-yu.tu@amlogic.com>

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


_______________________________________________
linux-amlogic mailing list
linux-amlogic@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-amlogic

  reply	other threads:[~2022-04-07  8:31 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-07  8:13 [PATCH 0/3] Use DIV_ROUND_CLOSEST to calculate baud rate, Yu Tu
2022-04-07  8:13 ` Yu Tu
2022-04-07  8:13 ` Yu Tu
2022-04-07  8:13 ` Yu Tu [this message]
2022-04-07  8:13   ` [PATCH 1/3] tty: serial: meson: Use DIV_ROUND_CLOSEST to calculate baud rates Yu Tu
2022-04-07  8:13   ` Yu Tu
2022-04-07 13:56   ` Neil Armstrong
2022-04-07 13:56     ` Neil Armstrong
2022-04-07 13:56     ` Neil Armstrong
2022-04-07  8:13 ` [PATCH 2/3] tty: serial: meson: Added 12Mhz as the clock source for calculating baud rate Yu Tu
2022-04-07  8:13   ` Yu Tu
2022-04-07  8:13   ` Yu Tu
2022-04-07 14:03   ` Neil Armstrong
2022-04-07 14:03     ` Neil Armstrong
2022-04-07 14:03     ` Neil Armstrong
2022-04-15 13:35     ` Yu Tu
2022-04-15 13:35       ` Yu Tu
2022-04-15 13:35       ` Yu Tu
2022-04-07  8:13 ` [PATCH 3/3] tty: serial: meson: Added S4 SOC compatibility Yu Tu
2022-04-07  8:13   ` Yu Tu
2022-04-07  8:13   ` Yu Tu

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