[PATCH 5.4 10/87] serial: mvebu-uart: correctly report configured baudrate value

Greg Kroah-Hartman
2022-07-27T16:38:17Z

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
@@ -443,13 +443,13 @@ 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)
{
unsigned int d_divisor, m_divisor;
u32 brdv, osamp;

if (!port->uartclk)
- return -EOPNOTSUPP;
+ return 0;

/*
* The baudrate is derived from the UART clock thanks to two divisors:
@@ -473,7 +473,7 @@ static int mvebu_uart_baud_rate_set(stru
osamp &= ~OSAMP_DIVISORS_MASK;
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,
@@ -510,15 +510,11 @@ 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) {
@@ -529,6 +525,11 @@ 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);
}