linux-kernel - [PATCH 3.16 245/328] serial: cpm_uart: return immediately from console poll

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Message-ID: <lsq.1544392233.965559385@decadent.org.uk>
Date:   Sun, 09 Dec 2018 21:50:33 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Jason Wessel" <jason.wessel@...driver.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Christophe Leroy" <christophe.leroy@....fr>
Subject: [PATCH 3.16 245/328] serial: cpm_uart: return immediately from
 console poll

3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Christophe Leroy <christophe.leroy@....fr>

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@...driver.com>
Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -1062,8 +1062,8 @@ 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.
@@ -1097,7 +1097,11 @@ 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--;