[PATCH 17/33] drm/vc4: hdmi: Disable audio if dmas property is present but empty

[Maxime Ripard <maxime@cerno.tech>]

From: Phil Elwell <phil@raspberrypi.org>

The dmas property is used to hold the dmaengine channel used for audio
output.

Older device trees were missing that property, so if it's not there we
disable the audio output entirely.

However, some overlays have set an empty value to that property, mostly
to workaround the fact that overlays cannot remove a property. Let's add
a test for that case and if it's empty, let's disable it as well.

Cc: <stable@vger.kernel.org>
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 6aadb65eb640..c8571e17afa8 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -2034,12 +2034,12 @@ static int vc4_hdmi_audio_init(struct vc4_hdmi *vc4_hdmi)
 	struct device *dev = &vc4_hdmi->pdev->dev;
 	struct platform_device *codec_pdev;
 	const __be32 *addr;
-	int index;
+	int index, len;
 	int ret;
 
-	if (!of_find_property(dev->of_node, "dmas", NULL)) {
+	if (!of_find_property(dev->of_node, "dmas", &len) || !len) {
 		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;
 	}
 
-- 
2.36.1