From: Alexey Starikovskiy <aystarik@xxxxxxxxx>
The problem with previous code was it rounded values in wrong
place and produced wrong baud rate in some cases.
Signed-off-by: Alexey Starikovskiy <aystarik@xxxxxxxxx>
[nicolas.ferre@xxxxxxxxx: port to newer kernel and add commit log]
Signed-off-by: Nicolas Ferre <nicolas.ferre@xxxxxxxxx>
---
drivers/tty/serial/atmel_serial.c | 10 ++++++----
include/linux/atmel_serial.h | 1 +
2 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 5f550d9feed9..fd8aa1f4ba78 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -2170,13 +2170,15 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
* accurately. This feature is enabled only when using normal mode.
* baudrate = selected clock / (8 * (2 - OVER) * (CD + FP / 8))
* Currently, OVER is always set to 0 so we get
- * baudrate = selected clock (16 * (CD + FP / 8))
+ * baudrate = selected clock / (16 * (CD + FP / 8))
+ * then
+ * 8 CD + FP = selected clock / (2 * baudrate)
*/
if (atmel_port->has_frac_baudrate &&
(mode & ATMEL_US_USMODE) == ATMEL_US_USMODE_NORMAL) {
- div = DIV_ROUND_CLOSEST(port->uartclk, baud);
- cd = div / 16;
- fp = DIV_ROUND_CLOSEST(div % 16, 2);
+ div = DIV_ROUND_CLOSEST(port->uartclk, baud * 2);
+ cd = div >> 3;
+ fp = div & ATMEL_US_FP_MASK;
} else {
cd = uart_get_divisor(port, baud);
}
diff --git a/include/linux/atmel_serial.h b/include/linux/atmel_serial.h
index f8e452aa48d7..bd2560502f3c 100644
--- a/include/linux/atmel_serial.h
+++ b/include/linux/atmel_serial.h
@@ -119,6 +119,7 @@
#define ATMEL_US_BRGR 0x20 /* Baud Rate Generator Register */
#define ATMEL_US_CD GENMASK(15, 0) /* Clock Divider */
#define ATMEL_US_FP_OFFSET 16 /* Fractional Part */
+#define ATMEL_US_FP_MASK 0x7
#define ATMEL_US_RTOR 0x24 /* Receiver Time-out Register for USART */
#define ATMEL_UA_RTOR 0x28 /* Receiver Time-out Register for UART */
--
2.9.0
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