drm/vc4: hdmi: Avoid full hdmi audio fifo writes

We are getting occasional VC4_HD_MAI_CTL_ERRORF in
HDMI_MAI_CTL which seem to correspond with audio dropouts.

Reduce the threshold where we deassert DREQ to avoid the fifo
overfilling

Fixes: bb7d7856 ("drm/vc4: Add HDMI audio support")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Link: https://lore.kernel.org/r/20220613144800.326124-21-maxime@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -1956,10 +1956,10 @@ static int vc4_hdmi_audio_prepare(struct device *dev, void *data,
 
 	/* Set the MAI threshold */
 	HDMI_WRITE(HDMI_MAI_THR,
-		   VC4_SET_FIELD(0x10, VC4_HD_MAI_THR_PANICHIGH) |
-		   VC4_SET_FIELD(0x10, VC4_HD_MAI_THR_PANICLOW) |
-		   VC4_SET_FIELD(0x10, VC4_HD_MAI_THR_DREQHIGH) |
-		   VC4_SET_FIELD(0x10, VC4_HD_MAI_THR_DREQLOW));
+		   VC4_SET_FIELD(0x08, VC4_HD_MAI_THR_PANICHIGH) |
+		   VC4_SET_FIELD(0x08, VC4_HD_MAI_THR_PANICLOW) |
+		   VC4_SET_FIELD(0x06, VC4_HD_MAI_THR_DREQHIGH) |
+		   VC4_SET_FIELD(0x08, VC4_HD_MAI_THR_DREQLOW));
 
 	HDMI_WRITE(HDMI_MAI_CONFIG,
 		   VC4_HDMI_MAI_CONFIG_BIT_REVERSE |