coresight: Change device mode to atomic type

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()")
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251111-arm_coresight_power_management_fix-v6-1-f55553b6c8b3@arm.com

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 56d0108658db34b8f2d184cd3214ca172a3ce808..2b48be97fcd0d7ea2692206692bd33f35ba4ec79 100644 (file)
--- 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 */
@@ -624,13 +620,14 @@ 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,
@@ -646,7 +643,7 @@ 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);