Fix Seaboard UART corruption on SPI activity

drivers/serial/ns16550.c

 /*
  * COM1 NS16550 support
  * originally from linux source (arch/powerpc/boot/ns16550.c)
  * modified to use CONFIG_SYS_ISA_MEM and new defines
  */
 
 #include <config.h>
 #include <ns16550.h>
 #include <watchdog.h>
 #include <linux/types.h>
@@ skipping 46 matching lines @@
         serial_out(0, &com_port->dll);
         serial_out(0, &com_port->dlm);
         serial_out(UART_LCRVAL, &com_port->lcr);
         serial_out(UART_MCRVAL, &com_port->mcr);
         serial_out(UART_FCRVAL, &com_port->fcr);
         serial_out(UART_LCR_BKSE, &com_port->lcr);
         serial_out(baud_divisor & 0xff, &com_port->dll);
         serial_out((baud_divisor >> 8) & 0xff, &com_port->dlm);
         serial_out(UART_LCRVAL, &com_port->lcr);
 }
+
+/* Clear the UART's RX FIFO */
+
+void NS16550_clear(NS16550_t com_port)
+{
+        /* Reset RX fifo */
+        serial_out(UART_FCR_FIFO_EN | UART_FCR_RXSR, &com_port->fcr);
+
+        /* Remove any pending characters */
+        while (NS16550_tstc(com_port))
+                NS16550_getc(com_port);
+}
+
+/* Wait for the UART's output buffer and holding register to drain */
+
+void NS16550_drain(NS16550_t com_port)
+{
+        /* Wait for the UART to finish sending */
+        while(!(serial_in(&com_port->lsr) & UART_LSR_TEMT))
+                udelay(100);
+
+        /*
+         * And a little while for the other end to get ready for the
+         * madness ahead.
+         */
+        udelay(100);
+}
+
 #endif /* CONFIG_NS16550_MIN_FUNCTIONS */
 
 void NS16550_putc (NS16550_t com_port, char c)
 {
         while ((serial_in(&com_port->lsr) & UART_LSR_THRE) == 0);
         serial_out(c, &com_port->thr);
 }
 
 #ifndef CONFIG_NS16550_MIN_FUNCTIONS
 char NS16550_getc (NS16550_t com_port)
 {
         while ((serial_in(&com_port->lsr) & UART_LSR_DR) == 0) {
 #ifdef CONFIG_USB_TTY
                 extern void usbtty_poll(void);
                 usbtty_poll();
 #endif
                 WATCHDOG_RESET();
         }
         return serial_in(&com_port->rbr);
 }
 
 int NS16550_tstc (NS16550_t com_port)
 {
         return ((serial_in(&com_port->lsr) & UART_LSR_DR) != 0);
 }
 
 #endif /* CONFIG_NS16550_MIN_FUNCTIONS */