diff --git a/drivers/hwtracing/intel_th/sth.c b/drivers/hwtracing/intel_th/sth.c
index 56101c33e10f..e1aee61dd7b3 100644
--- a/drivers/hwtracing/intel_th/sth.c
+++ b/drivers/hwtracing/intel_th/sth.c
@@ -94,10 +94,13 @@ static ssize_t sth_stm_packet(struct stm_data *stm_data, unsigned int master,
 	case STP_PACKET_TRIG:
 		if (flags & STP_PACKET_TIMESTAMPED)
 			reg += 4;
-		iowrite8(*payload, sth->base + reg);
+		writeb_relaxed(*payload, sth->base + reg);
 		break;
 
 	case STP_PACKET_MERR:
+		if (size > 4)
+			size = 4;
+
 		sth_iowrite(&out->MERR, payload, size);
 		break;
 
@@ -107,8 +110,8 @@ static ssize_t sth_stm_packet(struct stm_data *stm_data, unsigned int master,
 		else
 			outp = (u64 __iomem *)&out->FLAG;
 
-		size = 1;
-		sth_iowrite(outp, payload, size);
+		size = 0;
+		writeb_relaxed(0, outp);
 		break;
 
 	case STP_PACKET_USER:
@@ -129,6 +132,8 @@ static ssize_t sth_stm_packet(struct stm_data *stm_data, unsigned int master,
 
 		sth_iowrite(outp, payload, size);
 		break;
+	default:
+		return -ENOTSUPP;
 	}
 
 	return size;