From fd00cf81a9a84776ba58e56bd042c726dcf75cf3 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Fri, 3 Nov 2017 15:30:53 +0100
Subject: [PATCH] serdev: fix receive_buf return value when no callback
Git-commit: fd00cf81a9a84776ba58e56bd042c726dcf75cf3
Patch-mainline: v4.15-rc3
References: bsc#1051510

The receive_buf callback is supposed to return the number of bytes
processed and should specifically not return a negative errno.

Due to missing sanity checks in the serdev tty-port controller, a driver
not providing a receive_buf callback could cause the flush_to_ldisc()
worker to spin in a tight loop when the tty buffer pointers are
incremented with -EINVAL (-22).

The missing sanity checks have now been added to the tty-port
controller, but let's fix up the serdev-controller helper as well.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 include/linux/serdev.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -184,7 +184,7 @@ static inline int serdev_controller_rece
 	struct serdev_device *serdev = ctrl->serdev;
 
 	if (!serdev || !serdev->ops->receive_buf)
-		return -EINVAL;
+		return 0;
 
 	return serdev->ops->receive_buf(serdev, data, count);
 }