[F][PATCH 2/2] USB: serial: pl2303: fix line-speed handling on newer chips

[Aaron Ma]

From: Johan Hovold <johan at kernel.org>

BugLink: https://bugs.launchpad.net/bugs/1948377

The latest chip family (HXN) apparently does not support setting the
line speed using divisors and instead needs to use the direct encoding
scheme for all rates.

This specifically enables 50, 110, 134, 200 bps and other rates not
supported by the original chip type.

Fixes: ebd09f1cd417 ("USB: serial: pl2303: add support for PL2303HXN")
Cc: stable at vger.kernel.org      # 5.5
Cc: Charles Yeh <charlesyeh522 at gmail.com>
Signed-off-by: Johan Hovold <johan at kernel.org>
(cherry picked from commit 979d9cbe75b922ab1695b8ad5576115774f72e62)
Signed-off-by: Aaron Ma <aaron.ma at canonical.com>
---
 drivers/usb/serial/pl2303.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index 25b4333e9f85..67d2249cae22 100644
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -184,6 +184,7 @@ struct pl2303_type_data {
 	speed_t max_baud_rate;
 	unsigned long quirks;
 	unsigned int no_autoxonxoff:1;
+	unsigned int no_divisors:1;
 };
 
 struct pl2303_serial_private {
@@ -210,6 +211,7 @@ static const struct pl2303_type_data pl2303_type_data[TYPE_COUNT] = {
 	},
 	[TYPE_HXN] = {
 		.max_baud_rate		= 12000000,
+		.no_divisors		= true,
 	},
 };
 
@@ -572,8 +574,12 @@ static void pl2303_encode_baud_rate(struct tty_struct *tty,
 		baud = min_t(speed_t, baud, spriv->type->max_baud_rate);
 	/*
 	 * Use direct method for supported baud rates, otherwise use divisors.
+	 * Newer chip types do not support divisor encoding.
 	 */
-	baud_sup = pl2303_get_supported_baud_rate(baud);
+	if (spriv->type->no_divisors)
+		baud_sup = baud;
+	else
+		baud_sup = pl2303_get_supported_baud_rate(baud);
 
 	if (baud == baud_sup)
 		baud = pl2303_encode_baud_rate_direct(buf, baud);
-- 
2.30.2