scsi: ufs: Add exception event tracepoint

Currently, exception event status can be read from wExceptionEventStatus
attribute (sysfs file attributes/exception_event_status under the UFS host
controller device directory). Polling that attribute to track UFS exception
events is impractical, so add a tracepoint to track exception events for
testing and debugging purposes.

Note, by the time the exception event status is read, the exception event
may have cleared, so the value can be zero - see example below.

Note also, only enabled exception events can be reported. A subsequent
patch adds the ability for users to enable selected exception events via
debugfs.

Example with driver instrumented to enable all exception events:

  # echo 1 > /sys/kernel/debug/tracing/events/ufs/ufshcd_exception_event/enable

  ... do some I/O ...

  # cat /sys/kernel/debug/tracing/trace
  # tracer: nop
  #
  # entries-in-buffer/entries-written: 3/3   #P:5
  #
  #                                _-----=> irqs-off
  #                               / _----=> need-resched
  #                              | / _---=> hardirq/softirq
  #                              || / _--=> preempt-depth
  #                              ||| /     delay
  #           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
  #              | |         |   ||||      |         |
       kworker/2:2-173     [002] ....   731.486419: ufshcd_exception_event: 0000:00:12.5: status 0x0
       kworker/2:2-173     [002] ....   732.608918: ufshcd_exception_event: 0000:00:12.5: status 0x4
       kworker/2:2-173     [002] ....   732.609312: ufshcd_exception_event: 0000:00:12.5: status 0x4

Link: https://lore.kernel.org/r/20210209062437.6954-2-adrian.hunter@intel.comReviewed-by: Avri Altman <avri.altman@wdc.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ufs/ufshcd.c

@@ -5618,6 +5618,8 @@ static void ufshcd_exception_event_handler(struct work_struct *work)
 		goto out;
 	}
 
+	trace_ufshcd_exception_event(dev_name(hba->dev), status);
+
 	status &= hba->ee_ctrl_mask;
 
 	if (status & MASK_EE_URGENT_BKOPS)

include/trace/events/ufs.h

@@ -349,6 +349,27 @@ TRACE_EVENT(ufshcd_upiu,
 	)
 );
 
+TRACE_EVENT(ufshcd_exception_event,
+
+	TP_PROTO(const char *dev_name, u16 status),
+
+	TP_ARGS(dev_name, status),
+
+	TP_STRUCT__entry(
+		__string(dev_name, dev_name)
+		__field(u16, status)
+	),
+
+	TP_fast_assign(
+		__assign_str(dev_name, dev_name);
+		__entry->status = status;
+	),
+
+	TP_printk("%s: status 0x%x",
+		__get_str(dev_name), __entry->status
+	)
+);
+
 #endif /* if !defined(_TRACE_UFS_H) || defined(TRACE_HEADER_MULTI_READ) */
 
 /* This part must be outside protection */