From db2b927f8668adf3ac765e0921cd2720f5c04172 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Mon, 13 Jun 2022 16:47:44 +0200
Subject: [PATCH] drm/vc4: hdmi: Disable audio if dmas property is present but empty
Git-commit: db2b927f8668adf3ac765e0921cd2720f5c04172
Patch-mainline: v6.0-rc1
References: git-fixes

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>
Link: https://lore.kernel.org/r/20220613144800.326124-18-maxime@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/vc4/vc4_hdmi.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1542,12 +1542,12 @@ static int vc4_hdmi_audio_init(struct vc
 	struct snd_soc_card *card = &vc4_hdmi->audio.card;
 	struct device *dev = &vc4_hdmi->pdev->dev;
 	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;
 	}