[PATCH] vt: perform safe console erase in the right order

[Nicolas Pitre]

Commit 4b4ecd9cb853 ("vt: Perform safe console erase only once") removed
what appeared to be an extra call to scr_memsetw(). This missed the fact
that set_origin() must be called before clearing the screen otherwise
old screen content gets restored on the screen when using vgacon. Let's
fix that by moving all the scrollback handling to flush_scrollback()
where it logically belongs, and invoking it before the actual screen
clearing in csi_J(), making the code simpler in the end.

Reported-by: Matthew Whitehead <tedheads...@gmail.com>
Signed-off-by: Nicolas Pitre <n...@linaro.org>
Tested-by: Matthew Whitehead <tedheads...@gmail.com>
Fixes: 4b4ecd9cb853 ("vt: Perform safe console erase only once")
Cc: sta...@vger.kernel.org

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index bba75560d1..9646ff63e7 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -935,8 +935,11 @@ static void flush_scrollback(struct vc_data *vc)
 {
        WARN_CONSOLE_UNLOCKED();
 
+       set_origin(vc);
        if (vc->vc_sw->con_flush_scrollback)
                vc->vc_sw->con_flush_scrollback(vc);
+       else
+               vc->vc_sw->con_switch(vc);
 }
 
 /*
@@ -1503,8 +1506,10 @@ static void csi_J(struct vc_data *vc, int vpar)
                        count = ((vc->vc_pos - vc->vc_origin) >> 1) + 1;
                        start = (unsigned short *)vc->vc_origin;
                        break;
+               case 3: /* include scrollback */
+                       flush_scrollback(vc);
+                       /* fallthrough */
                case 2: /* erase whole display */
-               case 3: /* (and scrollback buffer later) */
                        vc_uniscr_clear_lines(vc, 0, vc->vc_rows);
                        count = vc->vc_cols * vc->vc_rows;
                        start = (unsigned short *)vc->vc_origin;
@@ -1513,13 +1518,7 @@ static void csi_J(struct vc_data *vc, int vpar)
                        return;
        }
        scr_memsetw(start, vc->vc_video_erase_char, 2 * count);
-       if (vpar == 3) {
-               set_origin(vc);
-               flush_scrollback(vc);
-               if (con_is_visible(vc))
-                       update_screen(vc);
-       } else if (con_should_update(vc))
-               do_update_region(vc, (unsigned long) start, count);
+       update_region(vc, (unsigned long) start, count);
        vc->vc_need_wrap = 0;
 }