linux-kernel - [PATCH V3 14/14] coresight: etm-perf: Add support for trace buffer format

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Date:   Wed, 27 Jan 2021 14:25:38 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org
Cc:     mathieu.poirier@...aro.org, suzuki.poulose@....com,
        mike.leach@...aro.org, lcherian@...vell.com,
        linux-kernel@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Leo Yan <leo.yan@...aro.org>
Subject: [PATCH V3 14/14] coresight: etm-perf: Add support for trace buffer format

From: Suzuki K Poulose <suzuki.poulose@....com>

CoreSight PMU supports aux-buffer for the ETM tracing. The trace
generated by the ETM (associated with individual CPUs, like Intel PT)
is captured by a separate IP (CoreSight TMC-ETR/ETF until now).

The TMC-ETR applies formatting of the raw ETM trace data, as it
can collect traces from multiple ETMs, with the TraceID to indicate
the source of a given trace packet.

Arm Trace Buffer Extension is new "sink" IP, attached to individual
CPUs and thus do not provide additional formatting, like TMC-ETR.

Additionally, a system could have both TRBE *and* TMC-ETR for
the trace collection. e.g, TMC-ETR could be used as a single
trace buffer to collect data from multiple ETMs to correlate
the traces from different CPUs. It is possible to have a
perf session where some events end up collecting the trace
in TMC-ETR while the others in TRBE. Thus we need a way
to identify the type of the trace for each AUX record.

Define the trace formats exported by the CoreSight PMU.
We don't define the flags following the "ETM" as this
information is available to the user when issuing
the session. What is missing is the additional
formatting applied by the "sink" which is decided
at the runtime and the user may not have a control on.

So we define :
 - CORESIGHT format (indicates the Frame format)
 - RAW format (indicates the format of the source)

The default value is CORESIGHT format for all the records
(i,e == 0). Add the RAW format for the TRBE sink driver.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mike Leach <mike.leach@...aro.org>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: Leo Yan <leo.yan@...aro.org>
Cc: Anshuman Khandual <anshuman.khandual@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 drivers/hwtracing/coresight/coresight-trbe.c | 2 ++
 include/uapi/linux/perf_event.h              | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
index 1464d8b..7c0e691 100644
--- a/drivers/hwtracing/coresight/coresight-trbe.c
+++ b/drivers/hwtracing/coresight/coresight-trbe.c
@@ -511,6 +511,7 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
 	if (cpudata->mode != CS_MODE_PERF)
 		return -EINVAL;

+	perf_aux_output_flag(handle, PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW);
 	/*
 	 * If the TRBE was disabled due to lack of space in the AUX buffer or a
 	 * spurious fault, the driver leaves it disabled, truncating the buffer.
@@ -606,6 +607,7 @@ static void trbe_handle_overflow(struct perf_output_handle *handle)
 	size = offset - PERF_IDX2OFF(handle->head, buf);
 	if (buf->snapshot)
 		handle->head = offset;
+	perf_aux_output_flag(handle, PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW);
 	perf_aux_output_end(handle, size);

 	event_data = perf_aux_output_begin(handle, event);
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 9a5ca45..169e6b3 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1111,6 +1111,10 @@ enum perf_callchain_context {
 #define PERF_AUX_FLAG_COLLISION			0x08	/* sample collided with another */
 #define PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK	0xff00	/* PMU specific trace format type */

+/* CoreSight PMU AUX buffer formats */
+#define PERF_AUX_FLAG_CORESIGHT_FORMAT_CORESIGHT	0x0000 /* Default for backward compatibility */
+#define PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW		0x0100 /* Raw format of the source */
+
 #define PERF_FLAG_FD_NO_GROUP		(1UL << 0)
 #define PERF_FLAG_FD_OUTPUT		(1UL << 1)
 #define PERF_FLAG_PID_CGROUP		(1UL << 2) /* pid=cgroup id, per-cpu mode only */
-- 
2.7.4