+From 8befbf55f2668a4dae739588ed3c0b0d06fccacd Mon Sep 17 00:00:00 2001
+From: Phil Elwell <phil@raspberrypi.org>
+Date: Wed, 31 Jul 2019 17:36:34 +0100
+Subject: [PATCH] drm/vc4: A present but empty dmas disables audio
+
+Overlays are unable to remove properties in the base DTB, but they
+can overwrite them. Allow a present but empty 'dmas' property
+to also disable the HDMI audio interface.
+
+See: https://github.com/raspberrypi/linux/issues/2489
+
+Signed-off-by: Phil Elwell <phil@raspberrypi.org>
+---
+ drivers/gpu/drm/vc4/vc4_hdmi.c | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
++++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
+@@ -1087,10 +1087,12 @@ static int vc4_hdmi_audio_init(struct vc
+ struct device *dev = &hdmi->pdev->dev;
+ const __be32 *addr;
+ int ret;
++ int len;
+
+- if (!of_find_property(dev->of_node, "dmas", NULL)) {
++ if (!of_find_property(dev->of_node, "dmas", &len) ||
++ len == 0) {
+ dev_warn(dev,
+- "'dmas' DT property is missing, no HDMI audio\n");
++ "'dmas' DT property is missing or empty, no HDMI audio\n");
+ return 0;
+ }
+