[PATCH v3 5/7] USB: serial: ftdi_sio: Fix baud rate rounding for ASYNC_SPD_CUST

["Pali Rohár" <pali@kernel.org>]

To compute more accurate baud rate when user uses ASYNC_SPD_CUST API,
use DIV_ROUND_CLOSEST() instead of just rounding down.

Rationale:
  Application uses old API, so it computes divisor D for baud rate B.

  The driver then tries to compute back the requested baud rate B, but
  rounds down in the division.

  Using rounding to closest value instead should increate accuracy here.

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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 1ab6bf48516f..718c86db2900 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1333,7 +1333,7 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
 	if (baud == 38400 &&
 	    ((priv->flags & ASYNC_SPD_MASK) == ASYNC_SPD_CUST) &&
 	     (priv->custom_divisor)) {
-		baud = priv->baud_base / priv->custom_divisor;
+		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);
 	}
-- 
2.20.1