drm/ast: Add helper to hide cursor

As the inverse to ast_cursor_show(), ast_cursor_hide() disables the
HW cursor.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200702115029.5281-9-tzimmermann@suse.de

drivers/gpu/drm/ast/ast_cursor.c

@@ -284,3 +284,8 @@ int ast_cursor_show(struct ast_private *ast, int x, int y,
 
 	return 0;
 }
+
+void ast_cursor_hide(struct ast_private *ast)
+{
+	ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xcb, 0xfc, 0x00);
+}

drivers/gpu/drm/ast/ast_drv.h

@@ -321,5 +321,6 @@ int ast_cursor_blit(struct ast_private *ast, struct drm_framebuffer *fb);
 void ast_cursor_page_flip(struct ast_private *ast);
 int ast_cursor_show(struct ast_private *ast, int x, int y,
 		    unsigned int offset_x, unsigned int offset_y);
+void ast_cursor_hide(struct ast_private *ast);
 
 #endif

drivers/gpu/drm/ast/ast_mode.c

@@ -683,7 +683,7 @@ ast_cursor_plane_helper_atomic_disable(struct drm_plane *plane,
 {
 	struct ast_private *ast = to_ast_private(plane->dev);
 
-	ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xcb, 0xfc, 0x00);
+	ast_cursor_hide(ast);
 }
 
 static const struct drm_plane_helper_funcs ast_cursor_plane_helper_funcs = {