linux-kernel - [PATCH] coresight: etm: Make cycle count threshold user configurable

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Date:   Tue,  8 Aug 2023 13:15:33 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Al.Grant@....com, Anshuman Khandual <anshuman.khandual@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>, coresight@...ts.linaro.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] coresight: etm: Make cycle count threshold user configurable

Cycle counting is enabled, when requested and supported but with a default
threshold value ETM_CYC_THRESHOLD_DEFAULT i.e 0x100 getting into TRCCCCTLR,
representing the minimum interval between cycle count trace packets.

This makes cycle threshold user configurable, from the user space via perf
event attributes. Although it falls back using ETM_CYC_THRESHOLD_DEFAULT,
in case no explicit request. As expected it creates a sysfs file as well.

/sys/bus/event_source/devices/cs_etm/format/cc_threshold

New 'cc_threshold' uses 'event->attr.config3' as no more space is available
in 'event->attr.config1' or 'event->attr.config2'.

Cc: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Mike Leach <mike.leach@...aro.org>
Cc: James Clark <james.clark@....com>
Cc: Leo Yan <leo.yan@...aro.org>
Cc: coresight@...ts.linaro.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
Changes in V2:

- s/treshhold/threshhold

Changes in V1:

https://lore.kernel.org/all/20230804044720.1478900-1-anshuman.khandual@arm.com/

 Documentation/trace/coresight/coresight.rst        |  2 ++
 drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 12 ++++++++++--
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
index 4a71ea6cb390..a698b07206b5 100644
--- a/Documentation/trace/coresight/coresight.rst
+++ b/Documentation/trace/coresight/coresight.rst
@@ -624,6 +624,8 @@ They are also listed in the folder /sys/bus/event_source/devices/cs_etm/format/
    * - timestamp
      - Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP
        <coresight-timestamp>`
+   * - cc_threshold
+     - Cycle count threshold value
 
 How to use the STM module
 -------------------------
diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 5ca6278baff4..09f75dffae60 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -68,6 +68,7 @@ PMU_FORMAT_ATTR(preset,		"config:0-3");
 PMU_FORMAT_ATTR(sinkid,		"config2:0-31");
 /* config ID - set if a system configuration is selected */
 PMU_FORMAT_ATTR(configid,	"config2:32-63");
+PMU_FORMAT_ATTR(cc_threshold,	"config3:0-11");
 
 
 /*
@@ -101,6 +102,7 @@ static struct attribute *etm_config_formats_attr[] = {
 	&format_attr_preset.attr,
 	&format_attr_configid.attr,
 	&format_attr_branch_broadcast.attr,
+	&format_attr_cc_threshold.attr,
 	NULL,
 };
 
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 9d186af81ea0..a353c0784bab 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -644,7 +644,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
 	struct etmv4_config *config = &drvdata->config;
 	struct perf_event_attr *attr = &event->attr;
 	unsigned long cfg_hash;
-	int preset;
+	int preset, cc_threshold;
 
 	/* Clear configuration from previous run */
 	memset(config, 0, sizeof(struct etmv4_config));
@@ -667,7 +667,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
 	if (attr->config & BIT(ETM_OPT_CYCACC)) {
 		config->cfg |= TRCCONFIGR_CCI;
 		/* TRM: Must program this for cycacc to work */
-		config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
+		cc_threshold = attr->config3 & ETM_CYC_THRESHOLD_MASK;
+		if (cc_threshold) {
+			if (cc_threshold < drvdata->ccitmin)
+				config->ccctlr = drvdata->ccitmin;
+			else
+				config->ccctlr = cc_threshold;
+		} else {
+			config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
+		}
 	}
 	if (attr->config & BIT(ETM_OPT_TS)) {
 		/*
-- 
2.25.1