tty: serial: fsl_lpuart: minimum baud rate support

The formula for the baud rate is
baud rate = "baud clock / ((OSR+1) × SBR)

Algorithm used in function lpuart32_serial_setbrg() only changes
the SBR. Even with maxmum value put in, OSR stays at 0x7 and the
lowest baud rate would be ~ 2600 bps

Update the algorithm to allow driver operation at 1200,2400 or 600 bps

Signed-off-by: Vabhav Sharma <vabhav.sharma@nxp.com>
Link: https://lore.kernel.org/r/1593170434-13524-1-git-send-email-vabhav.sharma@oss.nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 90298c4..7ca6422 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1925,6 +1925,9 @@ static void __lpuart32_serial_setbrg(struct uart_port *port,
                        tmp_sbr++;
                }
 
+               if (tmp_sbr > UARTBAUD_SBR_MASK)
+                       continue;
+
                if (tmp_diff <= baud_diff) {
                        baud_diff = tmp_diff;
                        osr = tmp_osr;