video: Provide a way to indicate the start of CLI entry

Add a new mark_start() method for the console, which indicates that the
CLI prompt has been written to the display and any following characters
will be user input.

There are two cases to consider, tracked by an indent flag in
struct vidconsole_cursor:

- normal CLI entry where new lines start at the left of the console
- expo entry where new lines start at the same position as the previous
  line (indent=true)

Record this position in the uclass info, so it is available to console
drivers.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/video/vidconsole-uclass.c

@@ -761,6 +761,25 @@ int vidconsole_set_cursor_visible(struct udevice *dev, bool visible,
 }
 #endif /* CONFIG_CURSOR */
 
+int vidconsole_mark_start(struct udevice *dev)
+{
+	struct vidconsole_priv *priv = dev_get_uclass_priv(dev);
+	struct vidconsole_ops *ops = vidconsole_get_ops(dev);
+
+	priv->xmark_frac = priv->xcur_frac;
+	priv->ymark = priv->ycur;
+	priv->cli_index = 0;
+	if (ops->mark_start) {
+		int ret;
+
+		ret = ops->mark_start(dev);
+		if (ret != -ENOSYS)
+			return ret;
+	}
+
+	return 0;
+}
+
 void vidconsole_push_colour(struct udevice *dev, enum colour_idx fg,
 			    enum colour_idx bg, struct vidconsole_colour *old)
 {
@@ -884,3 +903,23 @@ void vidconsole_set_bitmap_font(struct udevice *dev,
 void vidconsole_idle(struct udevice *dev)
 {
 }
+
+#ifdef CONFIG_CURSOR
+void vidconsole_readline_start(bool indent)
+{
+	struct uclass *uc;
+	struct udevice *dev;
+
+	uclass_id_foreach_dev(UCLASS_VIDEO_CONSOLE, dev, uc) {
+		struct vidconsole_priv *priv = dev_get_uclass_priv(dev);
+
+		priv->curs.indent = indent;
+		vidconsole_mark_start(dev);
+	}
+}
+
+void vidconsole_readline_end(void)
+{
+	/* TODO: mark the end */
+}
+#endif /* CURSOR */