[PATCH 4.4 80/85] tty: vt, consw->con_scrolldelta cleanup

[Greg Kroah-Hartman]

From: Jiri Slaby <jslaby@xxxxxxx>

commit 97293de977365fe672daec2523e66ef457104921 upstream.

* allow NULL consw->con_scrolldelta (some consoles define an empty
  hook)
* => remove empty hooks now
* return value of consw->con_scrolldelta is never checked => make the
  function void
* document consw->con_scrolldelta a bit

Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: Thomas Winischhofer <thomas@xxxxxxxxxxxxxxxx>
Cc: linux-usb@xxxxxxxxxxxxxxx
Cc: Jean-Christophe Plagniol-Villard <plagnioj@xxxxxxxxxxxx>
Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: linux-fbdev@xxxxxxxxxxxxxxx
Cc: linux-parisc@xxxxxxxxxxxxxxx
Cc: Ajay Kaher <akaher@xxxxxxxxxx>
[ for 4.4.y backport, only do the first change above, to prevent
.con_scrolldelta from being called if not present - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/vt/vt.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2484,7 +2484,7 @@ static void console_callback(struct work
 	if (scrollback_delta) {
 		struct vc_data *vc = vc_cons[fg_console].d;
 		clear_selection();
-		if (vc->vc_mode == KD_TEXT)
+		if (vc->vc_mode == KD_TEXT && vc->vc_sw->con_scrolldelta)
 			vc->vc_sw->con_scrolldelta(vc, scrollback_delta);
 		scrollback_delta = 0;
 	}