serial: serial_sh: bugfix: autoboot fails if serial console is not connected

On kzm9g board (rmobile SoC), autoboot fails if serial console cable is not
connected.  When serial cable is not connected, serial error occurs and
some garbage comes in data register.
sh_serial_tstc() in serial_sh.c does not check error status and misunderstand
there is some input data.  It is the reason that autoboot fails.
This patch adds checking error status in sh_serial_tstc().

This patch is based on v2013.01-rc1 tag of u-boot master git.

Signed-off-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>

drivers/serial/serial_sh.c

@@ -117,6 +117,14 @@ static int serial_rx_fifo_level(void)
 	return scif_rxfill(&sh_sci);
 }
 
+static void handle_error(void)
+{
+	sci_in(&sh_sci, SCxSR);
+	sci_out(&sh_sci, SCxSR, SCxSR_ERROR_CLEAR(&sh_sci));
+	sci_in(&sh_sci, SCLSR);
+	sci_out(&sh_sci, SCLSR, 0x00);
+}
+
 void serial_raw_putc(const char c)
 {
 	while (1) {
@@ -138,16 +146,14 @@ static void sh_serial_putc(const char c)
 
 static int sh_serial_tstc(void)
 {
+	if (sci_in(&sh_sci, SCxSR) & SCIF_ERRORS) {
+		handle_error();
+		return 0;
+	}
+
 	return serial_rx_fifo_level() ? 1 : 0;
 }
 
-void handle_error(void)
-{
-	sci_in(&sh_sci, SCxSR);
-	sci_out(&sh_sci, SCxSR, SCxSR_ERROR_CLEAR(&sh_sci));
-	sci_in(&sh_sci, SCLSR);
-	sci_out(&sh_sci, SCLSR, 0x00);
-}
 
 int serial_getc_check(void)
 {