When we use RS232 loopback, assume doing RTS change will cause
CTS change, DTR change will cause DCD/DSR change too.
Sometimes we got 7~4 bits of MSR changed but the 3~0 bits of
MSR(delta) maybe not changed when set & get MCR fasterly.
So we add more check not only UART_MSR_ANY_DELTA but also with
comparing DCD/RI/DSR/CTS change with old value. Due to the state
bit is always correct, we direct save msr when read.
The following step to reproduce this problem with while loop step 1~4:
1. ioctl(fd, TIOCMSET, &data) to set RTS or DTR
2. ioctl(fd, TIOCMGET, &data) to read CTS or DCD/DSR state
3. ioctl(fd, TIOCMSET, &data) to unset RTS or DTR
4. ioctl(fd, TIOCMGET, &data) to read CTS or DCD/DSR state
Signed-off-by: Peter Hung <hpeter+linux_kernel@xxxxxxxxx>
---
drivers/usb/serial/f81232.c | 23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)
diff --git a/drivers/usb/serial/f81232.c b/drivers/usb/serial/f81232.c
index c87a3eb..94c05d7 100644
--- a/drivers/usb/serial/f81232.c
+++ b/drivers/usb/serial/f81232.c
@@ -110,7 +110,8 @@ static void f81232_read_msr(struct usb_serial_port *port)
{
int status;
unsigned long flags;
- u8 current_msr;
+ u8 current_msr, prev_msr;
+ u8 msr_mask = ~UART_MSR_ANY_DELTA;
struct tty_struct *tty;
struct f81232_private *priv = usb_get_serial_port_data(port);
@@ -123,7 +124,21 @@ static void f81232_read_msr(struct usb_serial_port *port)
return;
}
- if (!(current_msr & UART_MSR_ANY_DELTA))
+ /*
+ * The 7~4 bits of MSR will change but the 3~0 bits of MSR(delta)
+ * maybe not change when set & get MCR fasterly.
+ *
+ * So we add more check with comparing DCD/RI/DSR/CTS
+ * change. and direct save msr when read.
+ */
+
+ spin_lock_irqsave(&priv->lock, flags);
+ prev_msr = priv->modem_status;
+ priv->modem_status = current_msr;
+ spin_unlock_irqrestore(&priv->lock, flags);
+
+ if (!(current_msr & UART_MSR_ANY_DELTA) &&
+ !((prev_msr ^ current_msr) & msr_mask))
return;
tty = tty_port_tty_get(&port->port);
@@ -136,10 +151,6 @@ static void f81232_read_msr(struct usb_serial_port *port)
tty_kref_put(tty);
}
- spin_lock_irqsave(&priv->lock, flags);
- priv->modem_status = current_msr;
- spin_unlock_irqrestore(&priv->lock, flags);
-
wake_up_interruptible(&port->port.delta_msr_wait);
}
--
1.9.1
--
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