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serial: mxs-auart: Fix baudrate calculation

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commit a6040bc610 upstream.

The reference manual for the i.MX28 recommends to calculate the divisor
as

	divisor = (UARTCLK * 32) / baud rate, rounded to the nearest integer

, so let's do this. For a typical setup of UARTCLK = 24 MHz and baud
rate = 115200 this changes the divisor from 6666 to 6667 and so the
actual baud rate improves from 115211.521 Bd (error ≅ 0.01 %) to
115194.240 Bd (error ≅ 0.005 %).

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Uwe Kleine-König
2017-03-20 10:05:38 +01:00
committed by Greg Kroah-Hartman
parent 67e41b1368
commit 5289f1ce39
1 changed files with 1 additions and 1 deletions
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2
drivers/tty/serial/mxs-auart.c
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@@ -1085,7 +1085,7 @@ static void mxs_auart_settermios(struct uart_port *u,
AUART_LINECTRL_BAUD_DIV_MAX);
baud_max = u->uartclk * 32 / AUART_LINECTRL_BAUD_DIV_MIN;
baud = uart_get_baud_rate(u, termios, old, baud_min, baud_max);
div = u->uartclk * 32 / baud;
div = DIV_ROUND_CLOSEST(u->uartclk * 32, baud);
}
ctrl |= AUART_LINECTRL_BAUD_DIVFRAC(div & 0x3F);