serial: cpm_uart: return immediately from console poll

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@windriver.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/tty/serial/cpm_uart/cpm_uart_core.c b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
index 24a5f05e769b..e5389591bb4f 100644
--- 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, struct uart_cpm_port *pinfo)
         /* 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_port *port)
                 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--;