openwrt/target/linux/bcm27xx/patches-5.4/950-0895-vc4_hdmi-Remove-firmware-logic-for-MAI-threshold-set.patch

From 5f22fca663178a49bbb72058ea9225d35b3d155d Mon Sep 17 00:00:00 2001
From: Dom Cobley <popcornmix@gmail.com>
Date: Thu, 25 Jun 2020 18:48:40 +0100
Subject: [PATCH] vc4_hdmi: Remove firmware logic for MAI threshold
 setting

This was a workaround for bugs in hardware on earlier Pi models
and wasn't totally successful.

It makes audio quality worse on a Pi4 at the higher sample rates

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -1010,22 +1010,12 @@ static int vc4_hdmi_audio_prepare(struct
 	audio_packet_config |= VC4_SET_FIELD(channel_mask,
 					     VC4_HDMI_AUDIO_PACKET_CEA_MASK);
 
-	/* Set the MAI threshold.  This logic mimics the firmware's. */
-	if (vc4_hdmi->audio.samplerate > 96000) {
-		HDMI_WRITE(HDMI_MAI_THR,
-			 VC4_SET_FIELD(0x12, VC4_HD_MAI_THR_DREQHIGH) |
-			 VC4_SET_FIELD(0x12, VC4_HD_MAI_THR_DREQLOW));
-	} else if (vc4_hdmi->audio.samplerate > 48000) {
-		HDMI_WRITE(HDMI_MAI_THR,
-			 VC4_SET_FIELD(0x14, VC4_HD_MAI_THR_DREQHIGH) |
-			 VC4_SET_FIELD(0x12, VC4_HD_MAI_THR_DREQLOW));
-	} else {
-		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));
-	}
+	/* 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));
 
 	HDMI_WRITE(HDMI_MAI_CONFIG,
 		   VC4_HDMI_MAI_CONFIG_BIT_REVERSE |