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.

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>

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index 0429c2a..93489fe 100644 (file)
--- 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);
 }