[PATCH 4.18 138/228] serial: cpm_uart: return immediately from console poll

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christophe Leroy <christophe.leroy@xxxxxx>

commit be28c1e3ca29887e207f0cbcd294cefe5074bab6 upstream.

kgdb expects poll function to return immediately and
returning NO_POLL_CHAR when no character is available.

Fixes: f5316b4aea024 ("kgdb,8250,pl011: Return immediately from console poll")
Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/cpm_uart/cpm_uart_core.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/tty/serial/cpm_uart/cpm_uart_core.c
+++ b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
@@ -1054,8 +1054,8 @@ static int poll_wait_key(char *obuf, str
 	/* Get the address of the host memory buffer.
 	 */
 	bdp = pinfo->rx_cur;
-	while (bdp->cbd_sc & BD_SC_EMPTY)
-		;
+	if (bdp->cbd_sc & BD_SC_EMPTY)
+		return NO_POLL_CHAR;
 
 	/* If the buffer address is in the CPM DPRAM, don't
 	 * convert it.
@@ -1090,7 +1090,11 @@ static int cpm_get_poll_char(struct uart
 		poll_chars = 0;
 	}
 	if (poll_chars <= 0) {
-		poll_chars = poll_wait_key(poll_buf, pinfo);
+		int ret = poll_wait_key(poll_buf, pinfo);
+
+		if (ret == NO_POLL_CHAR)
+			return ret;
+		poll_chars = ret;
 		pollp = poll_buf;
 	}
 	poll_chars--;