[Intel-gfx] [RFC 3/4] drm/i915/perf: Extract raw GPU timestamps from OA reports

[Sagar Arun Kamble]

From: Sourab Gupta <sourab.gupta at intel.com>

The OA reports contain the least significant 32 bits of the gpu timestamp.
This patch enables retrieval of the timestamp field from OA reports, to
forward as 64 bit raw gpu timestamps in the perf samples.

v2: Rebase w.r.t new timecounter support.

Signed-off-by: Sourab Gupta <sourab.gupta at intel.com>
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble at intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Sourab Gupta <sourab.gupta at intel.com>
Cc: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h  |  2 ++
 drivers/gpu/drm/i915/i915_perf.c | 26 +++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index e08bc85..5534cd2 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2151,6 +2151,8 @@ struct i915_perf_stream {
 	 */
 	struct i915_oa_config *oa_config;
 
+	u64 last_gpu_ts;
+
 	/**
 	 * System time correlation variables.
 	 */
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index f7e748c..3b721d7 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -575,6 +575,26 @@ static int append_oa_status(struct i915_perf_stream *stream,
 }
 
 /**
+ * get_gpu_ts_from_oa_report - Retrieve absolute gpu timestamp from OA report
+ *
+ * Note: We are assuming that we're updating last_gpu_ts frequently enough so
+ * that it's never possible to see multiple overflows before we compare
+ * sample_ts to last_gpu_ts. Since this is significantly large duration
+ * (~6min for 80ns ts base), we can safely assume so.
+ */
+static u64 get_gpu_ts_from_oa_report(struct i915_perf_stream *stream,
+				     const u8 *report)
+{
+	u32 sample_ts = *(u32 *)(report + 4);
+	u32 delta;
+
+	delta = sample_ts - (u32)stream->last_gpu_ts;
+	stream->last_gpu_ts += delta;
+
+	return stream->last_gpu_ts;
+}
+
+/**
  * append_oa_sample - Copies single OA report into userspace read() buffer.
  * @stream: An i915-perf stream opened for OA metrics
  * @buf: destination buffer given by userspace
@@ -622,7 +642,9 @@ static int append_oa_sample(struct i915_perf_stream *stream,
 	}
 
 	if (sample_flags & SAMPLE_GPU_TS) {
-		/* Timestamp to be populated from OA report */
+		/* Timestamp populated from OA report */
+		gpu_ts = get_gpu_ts_from_oa_report(stream, report);
+
 		if (copy_to_user(buf, &gpu_ts, I915_PERF_TS_SAMPLE_SIZE))
 			return -EFAULT;
 	}
@@ -2421,6 +2443,8 @@ static u64 i915_cyclecounter_read(const struct cyclecounter *cc)
 				    GEN7_TIMESTAMP_UDW);
 	intel_runtime_pm_put(dev_priv);
 
+	stream->last_gpu_ts = ts_count;
+
 	return ts_count;
 }
 
-- 
1.9.1