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Subject[PATCH V2 5/5] usb: serial: f81534: fix tx error on some baud rate
Date
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>
---
V2:
1: First introduced in this series patches.

drivers/usb/serial/f81534.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/usb/serial/f81534.c b/drivers/usb/serial/f81534.c
index a4666171239a..513805eeae6a 100644
--- a/drivers/usb/serial/f81534.c
+++ b/drivers/usb/serial/f81534.c
@@ -130,6 +130,7 @@
#define F81534_CLK_18_46_MHZ (F81534_UART_EN | BIT(1))
#define F81534_CLK_24_MHZ (F81534_UART_EN | BIT(2))
#define F81534_CLK_14_77_MHZ (F81534_UART_EN | BIT(1) | BIT(2))
+#define F81534_CLK_TX_DELAY_1BIT BIT(3)

#define F81534_CLK_RS485_MODE BIT(4)
#define F81534_CLK_RS485_INVERT BIT(5)
@@ -1438,6 +1439,11 @@ static int f81534_port_probe(struct usb_serial_port *port)
break;
}

+ /*
+ * 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_CLK_TX_DELAY_1BIT;
return f81534_set_port_output_pin(port);
}

--
2.7.4
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