[PATCH 4.19 52/62] serial: mvebu-uart: correctly report configured baudrate value

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Pali Rohár <pali@kernel.org>

commit 4f532c1e25319e42996ec18a1f473fd50c8e575d upstream.

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.

Fixes: 68a0db1d7da2 ("serial: mvebu-uart: add function to change baudrate")
Cc: stable <stable@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20220628100922.10717-1-pali@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/mvebu-uart.c |   25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -442,14 +442,14 @@ static void mvebu_uart_shutdown(struct u
 	}
 }
 
-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)
 {
 	struct mvebu_uart *mvuart = to_mvuart(port);
 	unsigned int d_divisor, m_divisor;
 	u32 brdv;
 
 	if (IS_ERR(mvuart->clk))
-		return -PTR_ERR(mvuart->clk);
+		return 0;
 
 	/*
 	 * The baudrate is derived from the UART clock thanks to two divisors:
@@ -469,7 +469,7 @@ static int mvebu_uart_baud_rate_set(stru
 	brdv |= d_divisor;
 	writel(brdv, port->membase + UART_BRDV);
 
-	return 0;
+	return DIV_ROUND_CLOSEST(port->uartclk, d_divisor * m_divisor);
 }
 
 static void mvebu_uart_set_termios(struct uart_port *port,
@@ -506,15 +506,11 @@ static void mvebu_uart_set_termios(struc
 	max_baud = 230400;
 
 	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) {
@@ -525,6 +521,11 @@ static void mvebu_uart_set_termios(struc
 		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);
 }