From c93f09402106f22601838ee2bb0d02bae934b5e5 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Wed, 7 Apr 2010 16:49:31 -0700
Subject: [PATCH] caif: check write operations

write is optional for a tty device. Check that we have a write op rather
than calling NULL.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
 drivers/net/caif/caif_serial.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c
index 3502f607117f..c669ec37483b 100644
--- a/drivers/net/caif/caif_serial.c
+++ b/drivers/net/caif/caif_serial.c
@@ -312,6 +312,10 @@ static int ldisc_open(struct tty_struct *tty)
 	char name[64];
 	int result;
 
+	/* No write no play */
+	if (tty->ops->write == NULL)
+		return -EOPNOTSUPP;
+
 	sprintf(name, "cf%s", tty->name);
 	dev = alloc_netdev(sizeof(*ser), name, caifdev_setup);
 	ser = netdev_priv(dev);
-- 
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