From cd097b7d08cef3c0e79f5d2ab2776c6c6b00a869 Mon Sep 17 00:00:00 2001
From: Dom Cobley <popcornmix@gmail.com>
Date: Tue, 10 Nov 2020 20:04:08 +0000
Subject: [PATCH] vc4: Clear unused infoframe packet RAM registers

Using a hdmi analyser the bytes in packet ram
registers beyond the length were visible in the
infoframes and it flagged the checksum as invalid.

Zeroing unused words of packet RAM avoids this

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -285,9 +285,11 @@ static void vc4_hdmi_write_infoframe(str
 	const struct vc4_hdmi_register *ram_packet_start =
 		&vc4_hdmi->variant->registers[HDMI_RAM_PACKET_START];
 	u32 packet_reg = ram_packet_start->offset + VC4_HDMI_PACKET_STRIDE * packet_id;
+	u32 packet_reg_next = ram_packet_start->offset +
+		VC4_HDMI_PACKET_STRIDE * (packet_id + 1);
 	void __iomem *base = __vc4_hdmi_get_field_base(vc4_hdmi,
 						       ram_packet_start->reg);
-	uint8_t buffer[VC4_HDMI_PACKET_STRIDE];
+	uint8_t buffer[VC4_HDMI_PACKET_STRIDE] = {};
 	ssize_t len, i;
 	int ret;
 
@@ -320,6 +322,13 @@ static void vc4_hdmi_write_infoframe(str
 		packet_reg += 4;
 	}
 
+	/*
+	 * clear remainder of packet ram as it's included in the
+	 * infoframe and triggers a checksum error on hdmi analyser
+	 */
+	for (; packet_reg < packet_reg_next; packet_reg += 4)
+		writel(0, base + packet_reg);
+
 	HDMI_WRITE(HDMI_RAM_PACKET_CONFIG,
 		   HDMI_READ(HDMI_RAM_PACKET_CONFIG) | BIT(packet_id));
 	ret = wait_for((HDMI_READ(HDMI_RAM_PACKET_STATUS) &
