[ 90/95] pmac_zilog,kdb: Fix console poll hook to return instead of loop

[Ben Hutchings]

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

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

From: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>

commit 38f8eefccf3a23c4058a570fa2938a4f553cf8e0 upstream.

kdb <-> kgdb transitioning does not work properly with this UART
driver because the get character routine loops indefinitely as opposed
to returning NO_POLL_CHAR per the expectation of the KDB I/O driver
API.

The symptom is a kernel hang when trying to switch debug modes.

Cc: Alan Cox <alan@xxxxxxxxxxxxxxx>
Signed-off-by: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/tty/serial/pmac_zilog.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/pmac_zilog.c b/drivers/tty/serial/pmac_zilog.c
index 654755a..333c8d0 100644
--- a/drivers/tty/serial/pmac_zilog.c
+++ b/drivers/tty/serial/pmac_zilog.c
@@ -1348,10 +1348,16 @@ static int pmz_verify_port(struct uart_port *port, struct serial_struct *ser)
 static int pmz_poll_get_char(struct uart_port *port)
 {
 	struct uart_pmac_port *uap = (struct uart_pmac_port *)port;
+	int tries = 2;
 
-	while ((read_zsreg(uap, R0) & Rx_CH_AV) == 0)
-		udelay(5);
-	return read_zsdata(uap);
+	while (tries) {
+		if ((read_zsreg(uap, R0) & Rx_CH_AV) != 0)
+			return read_zsdata(uap);
+		if (tries--)
+			udelay(5);
+	}
+
+	return NO_POLL_CHAR;
 }
 
 static void pmz_poll_put_char(struct uart_port *port, unsigned char c)


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