tty: vt, consw->con_scrolldelta cleanup

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@suse.cz>
Cc: Thomas Winischhofer <thomas@winischhofer.net>
Cc: linux-usb@vger.kernel.org
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: Ajay Kaher <akaher@vmware.com>
[ 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@linuxfoundation.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 0e4f54832fc792c4f669e7ae65f04ce6aed604e7..01aeffcdf9849e254289503bd2c1dc44917766c6 100644 (file)
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2484,7 +2484,7 @@ static void console_callback(struct work_struct *ignored)
        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;
        }