| Message ID | 20220407081355.13602-2-yu.tu@amlogic.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Use DIV_ROUND_CLOSEST to calculate baud rate, | expand |
On 07/04/2022 10:13, Yu Tu wrote: > 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); I check the calculations, and with DIV_ROUND_CLOSEST(), result is always closer to the required baudrate. Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
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);
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(-)