serial: cpm_uart: return immediately from console poll

BugLink: https://bugs.launchpad.net/bugs/1836287
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@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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/tty/serial/cpm_uart/cpm_uart_core.c b/drivers/tty/serial/cpm_uart/cpm_uart_core.c
index 24a5f05e769bee9f7972319c13fb84745773583c..e5389591bb4f1f83a207ee5be7e3577648972599 100644 (file)
--- 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--;