USB: serial: pl2303: fix line-speed handling on newer chips

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@vger.kernel.org      # 5.5
Cc: Charles Yeh <charlesyeh522@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index be8067017eaa53916b4fe9b9745741bdc5a10212..29dda60e3bcdefa254a549cf27b79ee67d00fe5e 100644 (file)
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -183,6 +183,7 @@ 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 {
@@ -209,6 +210,7 @@ static const struct pl2303_type_data pl2303_type_data[TYPE_COUNT] = {
        },
        [TYPE_HXN] = {
                .max_baud_rate          = 12000000,
+               .no_divisors            = true,
        },
 };
 
@@ -571,8 +573,12 @@ 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);