serial: xuartps: Do not enable parity error interrupt

The patch makes changes not to enable parity error interrupt.
With the current implementation, each parity error results in
two distinct interrupts (almost always). The first one is normal
parity error interrupt with no data in the fifo and the second one
is a proper Rx interrupt with the received data in the fifo. By
disabling parity error interrupt we still ensure handling of
parity errors as for the Rx fifo interrupt the parity error still
shows up in the interrupt status register. Considering the fact
that the by default INPCK and IGNPAR are not set, this is the
optimal implementation for parity error handling.

Signed-off-by: Anirudha Sarangi <anirudh@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
[stelford@cadence.com: cherry picked from
https://github.com/Xilinx/linux-xlnx commit
bf9f610b445e2c9ed33c41e1e0e30b43be4e1f97 with manual conflict
resolution]
Signed-off-by: Scott Telford <stelford@cadence.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -130,8 +130,21 @@ MODULE_PARM_DESC(rx_timeout, "Rx timeout, 1-255");
 #define CDNS_UART_IXR_RXEMPTY	0x00000002 /* RX FIFO empty interrupt. */
 #define CDNS_UART_IXR_MASK	0x00001FFF /* Valid bit mask */
 
-#define CDNS_UART_RX_IRQS	(CDNS_UART_IXR_PARITY | CDNS_UART_IXR_FRAMING | \
-				 CDNS_UART_IXR_OVERRUN | CDNS_UART_IXR_RXTRIG | \
+	/*
+	 * Do not enable parity error interrupt for the following
+	 * reason: When parity error interrupt is enabled, each Rx
+	 * parity error always results in 2 events. The first one
+	 * being parity error interrupt and the second one with a
+	 * proper Rx interrupt with the incoming data.  Disabling
+	 * parity error interrupt ensures better handling of parity
+	 * error events. With this change, for a parity error case, we
+	 * get a Rx interrupt with parity error set in ISR register
+	 * and we still handle parity errors in the desired way.
+	 */
+
+#define CDNS_UART_RX_IRQS	(CDNS_UART_IXR_FRAMING | \
+				 CDNS_UART_IXR_OVERRUN | \
+				 CDNS_UART_IXR_RXTRIG |	 \
 				 CDNS_UART_IXR_TOUT)
 
 /* Goes in read_status_mask for break detection as the HW doesn't do it*/