serial:ifx6x60:Prevent data transfer when IFX6x60 port is shutdown

This patch is to implement following 2 places to avoid potential error when IFX6x60 port shutdown:
1) Clear Flag IFX_SPI_STATE_IO_AVAILABLE to disable data transfer when Modem port is shutdown;
2) Clear Flag IFX_SPI_STATE_IO_IN_PROGRESS and IFX_SPI_STATE_IO_READY when reopen port.
This is because last port shutdown may happen when SPI/DMA transfer is in progress, if the last
data transfer is not completed(for example due to modem reset), the Flag IFX_SPI_STATE_IO_IN_PROGRESS
will be set forever, so when IFX port is activated again, IFX_SPI_STATE_IO_IN_PROGRESS will prevent
transferring data forever. And if don't clear IFX_SPI_STATE_IO_READY, it may cause one more SPI frame
transferring in spit there is not data need to be transfer.

cc: liu chuansheng <[e-mail]>
cc: Chen Jun <[e-mail]>
Signed-off-by: channing <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/ifx6x60.c

···
 	/* clear any old data; can't do this in 'close' */
 	kfifo_reset(&ifx_dev->tx_fifo);
 
+	/* clear any flag which may be set in port shutdown procedure */
+	clear_bit(IFX_SPI_STATE_IO_IN_PROGRESS, &ifx_dev->flags);
+	clear_bit(IFX_SPI_STATE_IO_READY, &ifx_dev->flags);
+
 	/* put port data into this tty */
 	tty->driver_data = ifx_dev;
 
 	/* allows flip string push from int context */
 	tty->low_latency = 1;
+
+	/* set flag to allows data transfer */
+	set_bit(IFX_SPI_STATE_IO_AVAILABLE, &ifx_dev->flags);
 
 	return 0;
 }
···
 	struct ifx_spi_device *ifx_dev =
 		container_of(port, struct ifx_spi_device, tty_port);
 
+	clear_bit(IFX_SPI_STATE_IO_AVAILABLE, &ifx_dev->flags);
 	mrdy_set_low(ifx_dev);
 	clear_bit(IFX_SPI_STATE_TIMER_PENDING, &ifx_dev->flags);
 	tasklet_kill(&ifx_dev->io_work_tasklet);
···
 	int retval;
 	struct ifx_spi_device *ifx_dev = (struct ifx_spi_device *) data;
 
-	if (!test_and_set_bit(IFX_SPI_STATE_IO_IN_PROGRESS, &ifx_dev->flags)) {
+	if (!test_and_set_bit(IFX_SPI_STATE_IO_IN_PROGRESS, &ifx_dev->flags) &&
+		test_bit(IFX_SPI_STATE_IO_AVAILABLE, &ifx_dev->flags)) {
 		if (ifx_dev->gpio.unack_srdy_int_nb > 0)
 			ifx_dev->gpio.unack_srdy_int_nb--;
 

drivers/tty/serial/ifx6x60.h

···
 #define IFX_SPI_STATE_IO_IN_PROGRESS	1
 #define IFX_SPI_STATE_IO_READY		2
 #define IFX_SPI_STATE_TIMER_PENDING	3
+#define IFX_SPI_STATE_IO_AVAILABLE	4
 
 /* flow control bitfields */
 #define IFX_SPI_DCD			0