linux-kernel - [PATCH v2] tty: serial: fsl_lpuart: minimum baud rate support

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Message-Id: <1593170434-13524-1-git-send-email-vabhav.sharma@oss.nxp.com>
Date:   Fri, 26 Jun 2020 16:50:34 +0530
From:   Vabhav Sharma <vabhav.sharma@....nxp.com>
To:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     v.sethi@....com, Vabhav Sharma <vabhav.sharma@....com>
Subject: [PATCH v2] tty: serial: fsl_lpuart: minimum baud rate support

From: Vabhav Sharma <vabhav.sharma@....com>

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@....com>
---
V2:
 - Incorporated review comment from Greg
---
 drivers/tty/serial/fsl_lpuart.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 90298c4..7ca6422 100644
--- 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;
-- 
2.7.4