coresight: Add helper for setting csdev->mode

Now that mode is in struct coresight_device, sets can be wrapped. This
also allows us to add a sanity check that there have been no concurrent
modifications of mode. Currently all usages of local_set() were inside
the device's spin locks so this new warning shouldn't be triggered.

coresight_take_mode() could maybe have been used in place of adding
the warning, but there may be use cases which set the mode to the same
mode which are valid but would fail in coresight_take_mode() because
it requires the device to only be in the disabled state.

Signed-off-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20240129154050.569566-13-james.clark@arm.com
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index a49e4e20e899..5f288d475490 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -596,6 +596,22 @@ static inline enum cs_mode coresight_get_mode(struct coresight_device *csdev)
 	return local_read(&csdev->mode);
 }
 
+static inline void coresight_set_mode(struct coresight_device *csdev,
+				      enum cs_mode new_mode)
+{
+	enum cs_mode current_mode = coresight_get_mode(csdev);
+
+	/*
+	 * Changing to a new mode must be done from an already disabled state
+	 * unless it's synchronized with coresight_take_mode(). Otherwise the
+	 * device is already in use and signifies a locking issue.
+	 */
+	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);
+}
+
 extern struct coresight_device *
 coresight_register(struct coresight_desc *desc);
 extern void coresight_unregister(struct coresight_device *csdev);