tty: xuartps: support 64 byte FIFO size

Changes to use the 64 byte FIFO depth and fix the issue
by clearing the txempty interrupt in isr status for tx
after filling in data in start_tx function
Signed-off-by: Suneel Garapati <suneelg@xilinx.com>
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -33,12 +33,22 @@
 #define XUARTPS_MAJOR		0	/* use dynamic node allocation */
 #define XUARTPS_MINOR		0	/* works best with devtmpfs */
 #define XUARTPS_NR_PORTS	2
-#define XUARTPS_FIFO_SIZE	16	/* FIFO size */
+#define XUARTPS_FIFO_SIZE	64	/* FIFO size */
 #define XUARTPS_REGISTER_SPACE	0xFFF
 
 #define xuartps_readl(offset)		ioread32(port->membase + offset)
 #define xuartps_writel(val, offset)	iowrite32(val, port->membase + offset)
 
+/* Rx Trigger level */
+static int rx_trigger_level = 56;
+module_param(rx_trigger_level, uint, S_IRUGO);
+MODULE_PARM_DESC(rx_trigger_level, "Rx trigger level, 1-63 bytes");
+
+/* Rx Timeout */
+static int rx_timeout = 10;
+module_param(rx_timeout, uint, S_IRUGO);
+MODULE_PARM_DESC(rx_timeout, "Rx timeout, 1-255");
+
 /********************************Register Map********************************/
 /** UART
  *
@@ -394,7 +404,7 @@ static void xuartps_start_tx(struct uart_port *port)
 		port->state->xmit.tail = (port->state->xmit.tail + 1) &
 					(UART_XMIT_SIZE - 1);
 	}
-
+	xuartps_writel(XUARTPS_IXR_TXEMPTY, XUARTPS_ISR_OFFSET);
 	/* Enable the TX Empty interrupt */
 	xuartps_writel(XUARTPS_IXR_TXEMPTY, XUARTPS_IER_OFFSET);
 
@@ -528,7 +538,7 @@ static void xuartps_set_termios(struct uart_port *port,
 			| (XUARTPS_CR_TX_EN | XUARTPS_CR_RX_EN),
 			XUARTPS_CR_OFFSET);
 
-	xuartps_writel(10, XUARTPS_RXTOUT_OFFSET);
+	xuartps_writel(rx_timeout, XUARTPS_RXTOUT_OFFSET);
 
 	port->read_status_mask = XUARTPS_IXR_TXEMPTY | XUARTPS_IXR_RXTRIG |
 			XUARTPS_IXR_OVERRUN | XUARTPS_IXR_TOUT;
@@ -631,11 +641,17 @@ static int xuartps_startup(struct uart_port *port)
 		| XUARTPS_MR_PARITY_NONE | XUARTPS_MR_CHARLEN_8_BIT,
 		 XUARTPS_MR_OFFSET);
 
-	/* Set the RX FIFO Trigger level to 14 assuming FIFO size as 16 */
-	xuartps_writel(14, XUARTPS_RXWM_OFFSET);
+	/*
+	 * Set the RX FIFO Trigger level to use most of the FIFO, but it
+	 * can be tuned with a module parameter
+	 */
+	xuartps_writel(rx_trigger_level, XUARTPS_RXWM_OFFSET);
 
-	/* Receive Timeout register is enabled with value of 10 */
-	xuartps_writel(10, XUARTPS_RXTOUT_OFFSET);
+	/*
+	 * Receive Timeout register is enabled but it
+	 * can be tuned with a module parameter
+	 */
+	xuartps_writel(rx_timeout, XUARTPS_RXTOUT_OFFSET);
 
 	/* Clear out any pending interrupts before enabling them */
 	xuartps_writel(xuartps_readl(XUARTPS_ISR_OFFSET), XUARTPS_ISR_OFFSET);