linux-kernel - [PATCH 12/17] coresight etr: Relax collection of trace from sysfs mode

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Date:   Thu, 19 Oct 2017 18:15:48 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, rob.walker@....com,
        mike.leach@...aro.org, coresight@...ts.linaro.org,
        mathieu.poirier@...aro.org,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH 12/17] coresight etr: Relax collection of trace from sysfs mode

Since the ETR now uses mode specific buffers, we can reliably
provide the trace data captured in sysfs mode, even when the ETR
is operating in PERF mode.

Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index ef7498f05b34..31353fc34b53 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1231,19 +1231,17 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
 		goto out;
 	}
 
-	/* Don't interfere if operated from Perf */
-	if (drvdata->mode == CS_MODE_PERF) {
-		ret = -EINVAL;
-		goto out;
-	}
-
-	/* If sysfs_buf is NULL the trace data has been read already */
+	/*
+	 * We can safely allow reads even if the ETR is operating in PERF mode,
+	 * since the sysfs session is captured in mode specific data.
+	 * If drvdata::sysfs_data is NULL the trace data has been read already.
+	 */
 	if (!drvdata->sysfs_buf) {
 		ret = -EINVAL;
 		goto out;
 	}
 
-	/* Disable the TMC if we are trying to read from a running session */
+	/* Disable the TMC if we are trying to read from a running session. */
 	if (drvdata->mode == CS_MODE_SYSFS)
 		tmc_etr_disable_hw(drvdata);
 
-- 
2.13.6