diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 5833a6997fd66..074afabaf0844 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -654,7 +654,7 @@ static int vc4_hdmi_write_infoframe(struct drm_connector *connector,
 	if (!drm_dev_enter(drm, &idx))
 		return 0;
 
-	if (len > sizeof(buffer)) {
+	if (len > VC4_HDMI_PACKET_SIZE) {
 		ret = -ENOMEM;
 		goto out;
 	}
@@ -680,6 +680,9 @@ static int vc4_hdmi_write_infoframe(struct drm_connector *connector,
 		       base + packet_reg);
 		packet_reg += 4;
 
+		if (packet_reg >= packet_reg_next)
+			break;
+
 		writel(buffer[i + 3] << 0 |
 		       buffer[i + 4] << 8 |
 		       buffer[i + 5] << 16 |
diff --git a/drivers/gpu/drm/vc4/vc4_hdmi_regs.h b/drivers/gpu/drm/vc4/vc4_hdmi_regs.h
index 59bfd69f54d98..fb97e8a72b59f 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi_regs.h
+++ b/drivers/gpu/drm/vc4/vc4_hdmi_regs.h
@@ -7,6 +7,12 @@
 
 #define VC4_HDMI_PACKET_STRIDE			0x24
 
+/*
+ * A packet RAM slot is 9 words, holding a 3-byte packet header followed by
+ * four 7-byte subpackets, so only 31 of its 36 bytes are addressable.
+ */
+#define VC4_HDMI_PACKET_SIZE			31
+
 enum vc4_hdmi_regs {
 	VC4_INVALID = 0,
 	VC4_HDMI,