[PATCH v8 09/23] coresight: syscfg: Use spinlock to protect active variables

[Leo Yan]

To support dynamically enabling and disabling the CoreSight path during
CPU idle, cscfg_config_sysfs_get_active_cfg() may be called by the ETM
driver in an atomic context. However, the function currently acquires a
mutex, which is a sleepable lock, and this is not allowed in atomic
context.

To make cscfg_config_sysfs_get_active_cfg() called in the idle flow,
replace the mutex with a raw spinlock to protect the active
variables.

Acquire the raw spinlock with IRQ-safe to avoid lockdep complaint.

Reviewed-by: James Clark <james.clark at linaro.org>
Tested-by: James Clark <james.clark at linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun at arm.com>
Signed-off-by: Leo Yan <leo.yan at arm.com>
---
 drivers/hwtracing/coresight/coresight-syscfg.c | 21 ++++++++++-----------
 drivers/hwtracing/coresight/coresight-syscfg.h |  2 ++
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
index d7f5037953d6ba7fb7f83a8012a1abc5ffd0a147..7e070787e18b47bc4be17b0f9821267268600513 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg.c
@@ -953,19 +953,21 @@ int cscfg_config_sysfs_activate(struct cscfg_config_desc *config_desc, bool acti
 	unsigned long cfg_hash;
 	int err = 0;
 
-	mutex_lock(&cscfg_mutex);
+	guard(mutex)(&cscfg_mutex);
 
 	cfg_hash = (unsigned long)config_desc->event_ea->var;
 
+	guard(raw_spinlock_irqsave)(&cscfg_mgr->sysfs_store_lock);
+
 	if (activate) {
 		/* cannot be a current active value to activate this */
 		if (cscfg_mgr->sysfs_active_config) {
 			err = -EBUSY;
-			goto exit_unlock;
+		} else {
+			err = _cscfg_activate_config(cfg_hash);
+			if (!err)
+				cscfg_mgr->sysfs_active_config = cfg_hash;
 		}
-		err = _cscfg_activate_config(cfg_hash);
-		if (!err)
-			cscfg_mgr->sysfs_active_config = cfg_hash;
 	} else {
 		/* disable if matching current value */
 		if (cscfg_mgr->sysfs_active_config == cfg_hash) {
@@ -975,17 +977,14 @@ int cscfg_config_sysfs_activate(struct cscfg_config_desc *config_desc, bool acti
 			err = -EINVAL;
 	}
 
-exit_unlock:
-	mutex_unlock(&cscfg_mutex);
 	return err;
 }
 
 /* set the sysfs preset value */
 void cscfg_config_sysfs_set_preset(int preset)
 {
-	mutex_lock(&cscfg_mutex);
+	guard(raw_spinlock_irqsave)(&cscfg_mgr->sysfs_store_lock);
 	cscfg_mgr->sysfs_active_preset = preset;
-	mutex_unlock(&cscfg_mutex);
 }
 
 /*
@@ -994,10 +993,9 @@ void cscfg_config_sysfs_set_preset(int preset)
  */
 void cscfg_config_sysfs_get_active_cfg(unsigned long *cfg_hash, int *preset)
 {
-	mutex_lock(&cscfg_mutex);
+	guard(raw_spinlock_irqsave)(&cscfg_mgr->sysfs_store_lock);
 	*preset = cscfg_mgr->sysfs_active_preset;
 	*cfg_hash = cscfg_mgr->sysfs_active_config;
-	mutex_unlock(&cscfg_mutex);
 }
 EXPORT_SYMBOL_GPL(cscfg_config_sysfs_get_active_cfg);
 
@@ -1201,6 +1199,7 @@ static int cscfg_create_device(void)
 	INIT_LIST_HEAD(&cscfg_mgr->load_order_list);
 	atomic_set(&cscfg_mgr->sys_active_cnt, 0);
 	cscfg_mgr->load_state = CSCFG_NONE;
+	raw_spin_lock_init(&cscfg_mgr->sysfs_store_lock);
 
 	/* setup the device */
 	dev = cscfg_device();
diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
index 66e2db890d8203853a0c3c907b48aa66dd8014e6..658e93c3705f1cb3ba3523d0bc27ac704697dd70 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.h
+++ b/drivers/hwtracing/coresight/coresight-syscfg.h
@@ -42,6 +42,7 @@ enum cscfg_load_ops {
  * @sysfs_active_config:Active config hash used if CoreSight controlled from sysfs.
  * @sysfs_active_preset:Active preset index used if CoreSight controlled from sysfs.
  * @load_state:		A multi-stage load/unload operation is in progress.
+ * @sysfs_store_lock:	Exclusive access sysfs stored variables.
  */
 struct cscfg_manager {
 	struct device dev;
@@ -54,6 +55,7 @@ struct cscfg_manager {
 	u32 sysfs_active_config;
 	int sysfs_active_preset;
 	enum cscfg_load_ops load_state;
+	raw_spinlock_t sysfs_store_lock;
 };
 
 /* get reference to dev in cscfg_manager */

-- 
2.34.1