linux-kernel - [PATCH] serial: mvebu-uart: correctly report configured baudrate value

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Date:   Tue, 28 Jun 2022 12:09:22 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Allen Yan <yanwei@...vell.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Gregory CLEMENT <gregory.clement@...tlin.com>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] serial: mvebu-uart: correctly report configured baudrate value

Functions tty_termios_encode_baud_rate() and uart_update_timeout() should
be called with the baudrate value which was set to hardware. Linux then
report exact values via ioctl(TCGETS2) to userspace.

Change mvebu_uart_baud_rate_set() function to return baudrate value which
was set to hardware and propagate this value to above mentioned functions.

With this change userspace would see precise value in termios c_ospeed
field.

Signed-off-by: Pali Rohár <pali@...nel.org>
Fixes: 68a0db1d7da2 ("serial: mvebu-uart: add function to change baudrate")
---
 drivers/tty/serial/mvebu-uart.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index 0429c2a54290..93489fe334d0 100644
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -470,14 +470,14 @@ static void mvebu_uart_shutdown(struct uart_port *port)
 	}
 }
 
-static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
+static unsigned int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
 {
 	unsigned int d_divisor, m_divisor;
 	unsigned long flags;
 	u32 brdv, osamp;
 
 	if (!port->uartclk)
-		return -EOPNOTSUPP;
+		return 0;
 
 	/*
 	 * The baudrate is derived from the UART clock thanks to divisors:
@@ -548,7 +548,7 @@ static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
 			(m_divisor << 16) | (m_divisor << 24);
 	writel(osamp, port->membase + UART_OSAMP);
 
-	return 0;
+	return DIV_ROUND_CLOSEST(port->uartclk, d_divisor * m_divisor);
 }
 
 static void mvebu_uart_set_termios(struct uart_port *port,
@@ -587,15 +587,11 @@ static void mvebu_uart_set_termios(struct uart_port *port,
 	max_baud = port->uartclk / 80;
 
 	baud = uart_get_baud_rate(port, termios, old, min_baud, max_baud);
-	if (mvebu_uart_baud_rate_set(port, baud)) {
-		/* No clock available, baudrate cannot be changed */
-		if (old)
-			baud = uart_get_baud_rate(port, old, NULL,
-						  min_baud, max_baud);
-	} else {
-		tty_termios_encode_baud_rate(termios, baud, baud);
-		uart_update_timeout(port, termios->c_cflag, baud);
-	}
+	baud = mvebu_uart_baud_rate_set(port, baud);
+
+	/* In case baudrate cannot be changed, report previous old value */
+	if (baud == 0 && old)
+		baud = tty_termios_baud_rate(old);
 
 	/* Only the following flag changes are supported */
 	if (old) {
@@ -606,6 +602,11 @@ static void mvebu_uart_set_termios(struct uart_port *port,
 		termios->c_cflag |= CS8;
 	}
 
+	if (baud != 0) {
+		tty_termios_encode_baud_rate(termios, baud, baud);
+		uart_update_timeout(port, termios->c_cflag, baud);
+	}
+
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
-- 
2.20.1