star64: Enable serial data available interrupt

The interrupt is enabled on init. Nothing needs to be done in the IRQ
handler as the next read will acknowledge the interrupt to the device.

Signed-off-by: Jimmy Brush <code@jimmah.com>

libplatsupport/src/plat/star64/serial.c

@@ -11,6 +11,8 @@
 #include "../../chardev.h"
 
 #define UART_THR 0x00 /* UART Transmit Holding Register */
+#define UART_IER 0x04 /* UART Interrupt Enable Register */
+#define UART_IER_ERDAI BIT(0) /* Enable Received Data Available Interrupt */
 #define UART_LSR 0x14 /* UART Line Status Register */
 #define UART_LSR_THRE 0x20 /* Transmit Holding Register Empty */
 
@@ -38,7 +40,11 @@ int uart_putchar(ps_chardevice_t *d, int c)
 
 static void uart_handle_irq(ps_chardevice_t *dev)
 {
-    /* This UART driver is not interrupt driven, there is nothing to do here. */
+    /*
+     * This is currently only called when received data is available on the device.
+     * The interrupt will be acked to the device on the next read to the device.
+     * There's nothing else we need to do here.
+     */
 }
 
 int uart_init(const struct dev_defn *defn,
@@ -63,6 +69,7 @@ int uart_init(const struct dev_defn *defn,
     dev->flags      = SERIAL_AUTO_CR;
 
     *REG_PTR(dev->vaddr, 0x8) = 1;
+    *REG_PTR(dev->vaddr, UART_IER) = UART_IER_ERDAI;
 
     return 0;
 }