[PATCH v2 6/7] USB: serial: ftdi_sio: Fix custom_divisor and c_*speed for ASYNC_SPD_CUST

["Marek Behún" <kabel@kernel.org>]

From: Pali Rohár <pali@kernel.org>

When ASYNC_SPD_CUST is used, update custom_divisor and c_*speed fields
so that they correspond to the newly set baud rate value, so that
userspace GET ioctls will see the true baud rate that is being used.

Signed-off-by: Pali Rohár <pali@kernel.org>
Tested-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
---
 drivers/usb/serial/ftdi_sio.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 5db1293bb7a2..39e8c5d06157 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1303,6 +1303,7 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	struct device *dev = &port->dev;
+	int fix_custom_divisor = 0;
 	int div_value = 0;
 	int div_okay = 1;
 	int baud;
@@ -1317,6 +1318,7 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
 	if (baud == 38400 &&
 	    ((priv->flags & ASYNC_SPD_MASK) == ASYNC_SPD_CUST) &&
 	     (priv->custom_divisor)) {
+		fix_custom_divisor = 1;
 		baud = DIV_ROUND_CLOSEST(priv->baud_base, priv->custom_divisor);
 		dev_dbg(dev, "%s - custom divisor %d sets baud rate to %d\n",
 			__func__, priv->custom_divisor, baud);
@@ -1401,7 +1403,19 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
 			ftdi_chip_name[priv->chip_type]);
 	}
 
+	/* Fix deprecated async-compatible custom_divisor hack and update tty baud rate */
+	if (fix_custom_divisor) {
+		priv->custom_divisor = DIV_ROUND_CLOSEST(priv->baud_base, baud);
+		old_baud = baud;
+		baud = 38400;
+	}
+
 	tty_encode_baud_rate(tty, baud, baud);
+
+	/* For async-compatible custom_divisor store into TCGETS2 c_*speed fields real baud rate */
+	if (fix_custom_divisor)
+		tty->termios.c_ispeed = tty->termios.c_ospeed = old_baud;
+
 	return div_value;
 }
 
@@ -2674,6 +2688,8 @@ static void ftdi_set_termios(struct tty_struct *tty,
 		dev_dbg(ddev, "%s: forcing baud rate for this device\n", __func__);
 		tty_encode_baud_rate(tty, priv->force_baud,
 					priv->force_baud);
+		termios->c_ispeed = termios->c_ospeed =
+			DIV_ROUND_CLOSEST(priv->baud_base, priv->custom_divisor);
 	}
 
 	/* Force RTS-CTS if this device requires it. */
-- 
2.35.1