linux-kernel - [PATCH 4/4] coresight/etm3x: remove redundant usage of drvdata->spinlock

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Message-Id: <20241221165934.1161856-5-yeoreum.yun@arm.com>
Date: Sat, 21 Dec 2024 16:59:34 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: suzuki.poulose@....com,
	mike.leach@...aro.org,
	james.clark@...aro.org,
	alexander.shishkin@...ux.intel.com
Cc: coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH 4/4] coresight/etm3x: remove redundant usage of drvdata->spinlock

Remove redundant usage of drvdata->spinlock in etm_starting/dying_cpu()
by preventing cpu hotplug while enabling etm3x via sysfs since
 - perf and sysfs enable method are serialized by csdev->mode
 - etm_starting/dying_cpu() aren't called concurrently with
   etm_enable_perf/sysfs() because they're called in cpu offline status.
 - while etm_enable_sysfs(), config isn't changed since csdev->mode is
   not DISABLED.

Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
 .../coresight/coresight-etm3x-core.c          | 33 ++++++++-----------
 1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index c103f4c70f5d..5ec871979ef7 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -519,7 +519,12 @@ static int etm_enable_sysfs(struct coresight_device *csdev)
 	struct etm_enable_arg arg = { };
 	int ret;
 
-	spin_lock(&drvdata->spinlock);
+	cpus_read_lock();
+
+	if (cpu_is_offline(drvdata->cpu)) {
+		ret = -ENODEV;
+		goto unlock_sysfs_enable;
+	}
 
 	/* sysfs needs to allocate and set a trace ID */
 	ret = etm_read_alloc_trace_id(drvdata);
@@ -530,23 +535,19 @@ static int etm_enable_sysfs(struct coresight_device *csdev)
 	 * Configure the ETM only if the CPU is online.  If it isn't online
 	 * hw configuration will take place on the local CPU during bring up.
 	 */
-	if (cpu_online(drvdata->cpu)) {
-		arg.drvdata = drvdata;
-		ret = smp_call_function_single(drvdata->cpu,
-					       etm_enable_hw_smp_call, &arg, 1);
-		if (!ret)
-			ret = arg.rc;
-		if (!ret)
-			drvdata->sticky_enable = true;
-	} else {
-		ret = -ENODEV;
-	}
+	arg.drvdata = drvdata;
+	ret = smp_call_function_single(drvdata->cpu,
+				       etm_enable_hw_smp_call, &arg, 1);
+	if (!ret)
+		ret = arg.rc;
+	if (!ret)
+		drvdata->sticky_enable = true;
 
 	if (ret)
 		etm_release_trace_id(drvdata);
 
 unlock_enable_sysfs:
-	spin_unlock(&drvdata->spinlock);
+	cpus_read_unlock();
 
 	if (!ret)
 		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
@@ -646,7 +647,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
 	 * DYING hotplug callback is serviced by the ETM driver.
 	 */
 	cpus_read_lock();
-	spin_lock(&drvdata->spinlock);
 
 	/*
 	 * Executing etm_disable_hw on the cpu whose ETM is being disabled
@@ -654,7 +654,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
 	 */
 	smp_call_function_single(drvdata->cpu, etm_disable_hw, drvdata, 1);
 
-	spin_unlock(&drvdata->spinlock);
 	cpus_read_unlock();
 
 	/*
@@ -722,7 +721,6 @@ static int etm_starting_cpu(unsigned int cpu)
 	if (!etmdrvdata[cpu])
 		return 0;
 
-	spin_lock(&etmdrvdata[cpu]->spinlock);
 	if (!etmdrvdata[cpu]->os_unlock) {
 		etm_os_unlock(etmdrvdata[cpu]);
 		etmdrvdata[cpu]->os_unlock = true;
@@ -730,7 +728,6 @@ static int etm_starting_cpu(unsigned int cpu)
 
 	if (coresight_get_mode(etmdrvdata[cpu]->csdev))
 		etm_enable_hw(etmdrvdata[cpu]);
-	spin_unlock(&etmdrvdata[cpu]->spinlock);
 	return 0;
 }
 
@@ -739,10 +736,8 @@ static int etm_dying_cpu(unsigned int cpu)
 	if (!etmdrvdata[cpu])
 		return 0;
 
-	spin_lock(&etmdrvdata[cpu]->spinlock);
 	if (coresight_get_mode(etmdrvdata[cpu]->csdev))
 		etm_disable_hw(etmdrvdata[cpu]);
-	spin_unlock(&etmdrvdata[cpu]->spinlock);
 	return 0;
 }
 
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}