ASoC: SOF: mtrace: rework mtrace timestamp setting

The original timestamp is built base on windows epoch time which is not
fit for Linux system and difficult to be used for kernel debugging. This
patch adopts syslog timestamp so that we can simply use dmesg to check
the timestamp between fw and kernel.

Signed-off-by: Rander Wang <rander.wang@intel.com>

sound/soc/sof/ipc4-mtrace.c

@@ -4,6 +4,7 @@
 
 #include <linux/debugfs.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/clock.h>
 #include <sound/sof/ipc4/header.h>
 #include "sof-priv.h"
 #include "ipc4-priv.h"
@@ -412,7 +413,6 @@ static int ipc4_mtrace_enable(struct snd_sof_dev *sdev)
 	const struct sof_ipc_ops *iops = sdev->ipc->ops;
 	struct sof_ipc4_msg msg;
 	u64 system_time;
-	ktime_t kt;
 	int ret;
 
 	if (priv->mtrace_state != SOF_MTRACE_DISABLED)
@@ -424,9 +424,12 @@ static int ipc4_mtrace_enable(struct snd_sof_dev *sdev)
 	msg.primary |= SOF_IPC4_MOD_INSTANCE(SOF_IPC4_MOD_INIT_BASEFW_INSTANCE_ID);
 	msg.extension = SOF_IPC4_MOD_EXT_MSG_PARAM_ID(SOF_IPC4_FW_PARAM_SYSTEM_TIME);
 
-	/* The system time is in usec, UTC, epoch is 1601-01-01 00:00:00 */
-	kt = ktime_add_us(ktime_get_real(), FW_EPOCH_DELTA * USEC_PER_SEC);
-	system_time = ktime_to_us(kt);
+	/*
+	 * local_clock() is used to align with dmesg, so both kernel and firmware logs have
+	 * the same base and a minor delta due to the IPC. system time is in us format but
+	 * local_clock() returns the time in ns, so convert to ns.
+	 */
+	system_time = div64_u64(local_clock(), NSEC_PER_USEC);
 	msg.data_size = sizeof(system_time);
 	msg.data_ptr = &system_time;
 	ret = iops->set_get_data(sdev, &msg, msg.data_size, true);