USB: serial: f81534: fix tx error on some baud rate

The F81532/534 had 4 clocksource 1.846/18.46/14.77/24MHz and baud rates
can be up to 1.5Mbits with 24MHz. But on some baud rate (384~500kps), the
TX side will send the data frame too close to treat frame error on RX
side. This patch will force all TX data frame with delay 1bit gap.

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
index 86edec3e8c05..4dfbff20bda4 100644
--- a/drivers/usb/serial/f81534.c
+++ b/drivers/usb/serial/f81534.c
@@ -131,6 +131,7 @@
 #define F81534_CLK_24_MHZ               BIT(2)
 #define F81534_CLK_14_77_MHZ            (BIT(1) | BIT(2))
 #define F81534_CLK_MASK                 GENMASK(2, 1)
+#define F81534_CLK_TX_DELAY_1BIT        BIT(3)
 #define F81534_CLK_RS485_MODE           BIT(4)
 #define F81534_CLK_RS485_INVERT         BIT(5)
 
@@ -1386,7 +1387,11 @@ static int f81534_port_probe(struct usb_serial_port *port)
         if (!port_priv)
                 return -ENOMEM;
 
-        port_priv->shadow_clk = F81534_UART_EN;
+        /*
+         * We'll make tx frame error when baud rate from 384~500kps. So we'll
+         * delay all tx data frame with 1bit.
+         */
+        port_priv->shadow_clk = F81534_UART_EN | F81534_CLK_TX_DELAY_1BIT;
         spin_lock_init(&port_priv->msr_lock);
         mutex_init(&port_priv->mcr_mutex);
         mutex_init(&port_priv->lcr_mutex);