From: Phil Elwell <phil@raspberrypi.org>
Date: Wed, 31 Jul 2019 16:36:34 +0000 (+0100)
Subject: drm/vc4: A present but empty dmas disables audio
X-Git-Tag: accepted/tizen/unified/20200709.164653~994
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=81da133586449ae1d8e1a931a38216d188841c98;p=platform%2Fkernel%2Flinux-rpi.git

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>
---

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index d5f5ba4..0c3d9d2 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1066,10 +1066,12 @@ static int vc4_hdmi_audio_init(struct vc4_hdmi *hdmi)
 	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;
 	}