[PATCH v10 2/8] coresight: etm3x: fix inconsistencies with sysfs configuration

[Yeoreum Yun <yeoreum.yun@arm.com>]

The current ETM3x configuration via sysfs can lead to the following
inconsistencies:

  - If a configuration is modified via sysfs while a perf session is
    active, the running configuration may differ between before
    a sched-out and after a subsequent sched-in.

To resolve these issues, separate the configuration into:

  - active_config: the configuration applied to the current session
  - config: the configuration set via sysfs

Additionally:

  - Since active_config and related fields are accessed only by the local CPU
    in etm_enable/disable_sysfs_smp_call() (similar to perf enable/disable),
    remove the lock/unlock from the sysfs enable/disable path and
    starting/dying_cpu path except when to access config fields only.

Fixes: 1925a470ce69 ("coresight: etm3x: splitting struct etm_drvdata")
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 drivers/hwtracing/coresight/coresight-etm.h        |  4 ++-
 drivers/hwtracing/coresight/coresight-etm3x-core.c | 38 +++++++++++-----------
 2 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm.h b/drivers/hwtracing/coresight/coresight-etm.h
index 1d753cca2943..f3796162168d 100644
--- a/drivers/hwtracing/coresight/coresight-etm.h
+++ b/drivers/hwtracing/coresight/coresight-etm.h
@@ -226,7 +226,8 @@ struct etm_config {
  * @etmccr:	value of register ETMCCR.
  * @etmccer:	value of register ETMCCER.
  * @traceid:	value of the current ID for this component.
- * @config:	structure holding configuration parameters.
+ * @active_config:	structure holding current running configuration.
+ * @config:	structure holding sysfs mode configuration.
  */
 struct etm_drvdata {
 	struct csdev_access		csa;
@@ -248,6 +249,7 @@ struct etm_drvdata {
 	u32				etmccr;
 	u32				etmccer;
 	u32				traceid;
+	struct etm_config		active_config;
 	struct etm_config		config;
 };
 
diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index 862ad0786699..93dc98145b66 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -308,7 +308,7 @@ void etm_config_trace_mode(struct etm_config *config)
 static int etm_parse_event_config(struct etm_drvdata *drvdata,
 				  struct perf_event *event)
 {
-	struct etm_config *config = &drvdata->config;
+	struct etm_config *config = &drvdata->active_config;
 	struct perf_event_attr *attr = &event->attr;
 	u8 ts_level;
 
@@ -367,7 +367,7 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)
 {
 	int i, rc;
 	u32 etmcr;
-	struct etm_config *config = &drvdata->config;
+	struct etm_config *config = &drvdata->active_config;
 	struct coresight_device *csdev = drvdata->csdev;
 
 	CS_UNLOCK(drvdata->csa.base);
@@ -442,24 +442,30 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)
 struct etm_enable_arg {
 	struct etm_drvdata *drvdata;
 	struct coresight_path *path;
+	struct etm_config config;
 	int rc;
 };
 
 static void etm_enable_sysfs_smp_call(void *info)
 {
 	struct etm_enable_arg *arg = info;
+	struct etm_drvdata *drvdata;
 	struct coresight_device *csdev;
 
 	if (WARN_ON(!arg))
 		return;
 
-	csdev = arg->drvdata->csdev;
+	drvdata = arg->drvdata;
+	csdev = drvdata->csdev;
 	if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
 		/* Someone is already using the tracer */
 		arg->rc = -EBUSY;
 		return;
 	}
 
+	drvdata->active_config = arg->config;
+	drvdata->traceid = arg->path->trace_id;
+
 	arg->rc = etm_enable_hw(arg->drvdata);
 
 	/* The tracer didn't start */
@@ -468,6 +474,7 @@ static void etm_enable_sysfs_smp_call(void *info)
 		return;
 	}
 
+	drvdata->sticky_enable = true;
 	csdev->path = arg->path;
 }
 
@@ -512,10 +519,6 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
 	struct etm_enable_arg arg = { };
 	int ret;
 
-	spin_lock(&drvdata->spinlock);
-
-	drvdata->traceid = path->trace_id;
-
 	/*
 	 * 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.
@@ -523,23 +526,24 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
 	if (cpu_online(drvdata->cpu)) {
 		arg.drvdata = drvdata;
 		arg.path = path;
+
+		raw_spin_lock(&drvdata->spinlock);
+		arg.config = drvdata->config;
+		raw_spin_unlock(&drvdata->spinlock);
+
 		ret = smp_call_function_single(drvdata->cpu,
 					       etm_enable_sysfs_smp_call, &arg, 1);
 		if (!ret)
 			ret = arg.rc;
-		if (!ret)
-			drvdata->sticky_enable = true;
 	} else {
 		ret = -ENODEV;
 	}
 
-	if (ret)
-		etm_release_trace_id(drvdata);
-
-	spin_unlock(&drvdata->spinlock);
-
 	if (!ret)
 		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
+	else
+		etm_release_trace_id(drvdata);
+
 	return ret;
 }
 
@@ -565,7 +569,7 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
 static void etm_disable_hw(struct etm_drvdata *drvdata)
 {
 	int i;
-	struct etm_config *config = &drvdata->config;
+	struct etm_config *config = &drvdata->active_config;
 	struct coresight_device *csdev = drvdata->csdev;
 
 	CS_UNLOCK(drvdata->csa.base);
@@ -631,8 +635,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
 {
 	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
 
-	spin_lock(&drvdata->spinlock);
-
 	/*
 	 * Executing etm_disable_hw on the cpu whose ETM is being disabled
 	 * ensures that register writes occur when cpu is powered.
@@ -640,8 +642,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
 	smp_call_function_single(drvdata->cpu, etm_disable_sysfs_smp_call,
 				 drvdata, 1);
 
-	spin_unlock(&drvdata->spinlock);
-
 	/*
 	 * we only release trace IDs when resetting sysfs.
 	 * This permits sysfs users to read the trace ID after the trace

-- 
2.43.0