[PATCH v2 01/28] coresight: Change device mode to atomic type

[Leo Yan]

The device mode is defined as local type. This type cannot promise
SMP-safe access.

Change to atomic type and impose relax ordering, which ensures the
SMP-safe synchronisation and the ordering between the mode setting and
relevant operations.

Fixes: 22fd532eaa0c ("coresight: etm3x: adding operation mode for etm_enable()")
Signed-off-by: Leo Yan <leo.yan at arm.com>
---
 include/linux/coresight.h | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 4ac65c68bbf44b98db22c3dad2d83a224ce5278e..5fd3d08824e5a91a197aa01daf0fc392392f3e55 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -251,15 +251,11 @@ struct coresight_trace_id_map {
  *		by @coresight_ops.
  * @access:	Device i/o access abstraction for this device.
  * @dev:	The device entity associated to this component.
- * @mode:	This tracer's mode, i.e sysFS, Perf or disabled. This is
- *		actually an 'enum cs_mode', but is stored in an atomic type.
- *		This is always accessed through local_read() and local_set(),
- *		but wherever it's done from within the Coresight device's lock,
- *		a non-atomic read would also work. This is the main point of
- *		synchronisation between code happening inside the sysfs mode's
- *		coresight_mutex and outside when running in Perf mode. A compare
- *		and exchange swap is done to atomically claim one mode or the
- *		other.
+ * @mode:	The device mode, i.e sysFS, Perf or disabled. This is actually
+ *		an 'enum cs_mode' but stored in an atomic type. Access is always
+ *		through atomic APIs, ensuring SMP-safe synchronisation between
+ *		racing from sysFS and Perf mode. A compare-and-exchange
+ *		operation is done to atomically claim one mode or the other.
  * @refcnt:	keep track of what is in use. Only access this outside of the
  *		device's spinlock when the coresight_mutex held and mode ==
  *		CS_MODE_SYSFS. Otherwise it must be accessed from inside the
@@ -288,7 +284,7 @@ struct coresight_device {
 	const struct coresight_ops *ops;
 	struct csdev_access access;
 	struct device dev;
-	local_t	mode;
+	atomic_t mode;
 	int refcnt;
 	bool orphan;
 	/* sink specific fields */
@@ -650,13 +646,14 @@ static inline bool coresight_is_percpu_sink(struct coresight_device *csdev)
 static inline bool coresight_take_mode(struct coresight_device *csdev,
 				       enum cs_mode new_mode)
 {
-	return local_cmpxchg(&csdev->mode, CS_MODE_DISABLED, new_mode) ==
-	       CS_MODE_DISABLED;
+	int curr = CS_MODE_DISABLED;
+
+	return atomic_try_cmpxchg_acquire(&csdev->mode, &curr, new_mode);
 }
 
 static inline enum cs_mode coresight_get_mode(struct coresight_device *csdev)
 {
-	return local_read(&csdev->mode);
+	return atomic_read_acquire(&csdev->mode);
 }
 
 static inline void coresight_set_mode(struct coresight_device *csdev,
@@ -672,7 +669,7 @@ static inline void coresight_set_mode(struct coresight_device *csdev,
 	WARN(new_mode != CS_MODE_DISABLED && current_mode != CS_MODE_DISABLED &&
 	     current_mode != new_mode, "Device already in use\n");
 
-	local_set(&csdev->mode, new_mode);
+	atomic_set_release(&csdev->mode, new_mode);
 }
 
 struct coresight_device *coresight_register(struct coresight_desc *desc);

-- 
2.34.1