coresight: syscfg: Update load and unload operations

The configfs system is a source of access to the config information in the
configuration and feature lists.

This can result in additional LOCKDEP issues as a result of the mutex
ordering between the config list mutex (cscfg_mutex) and the configfs
system mutexes.

As such we need to adjust how load/unload operations work to ensure correct
operation.

1) Previously the cscfg_mutex was held throughout the load/unload
operation. This is now only held during configuration list manipulations,
resulting in a multi-stage load/unload process.

2) All operations that manipulate the configfs representation of the
configurations and features are now separated out and run without the
cscfg_mutex being held. This avoids circular lock_dep issue with the
built-in configfs mutexes and semaphores

3) As the load and unload is now multi-stage, some parts under the
cscfg_mutex and others not:
i) A flag indicating a load / unload operation in progress is used to
serialise load / unload operations.
ii) activating any configuration not possible when unload is in progress.
iii) Configurations have an "available" flag set only after the last load
stage for the configuration is complete. Activation of the configuration
not possible till flag is set.

4) Following load/unload rules remain:
i) Unload prevented while any configuration is active remains.
ii) Unload in strict reverse order of load.
iii) Existing configurations can be activated while a new load operation
is underway. (by definition there can be no dependencies between an
existing configuration and a new loading one due to ii) above.)

Fixes: eb2ec49606c2 ("coresight: syscfg: Update load API for config loadable modules")
Reported-by: Suzuki Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mike Leach <mike.leach@linaro.org>
Reviewed-and-tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20220628173004.30002-3-mike.leach@linaro.org
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
index 9106ffab4833..66e2db890d82 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.h
+++ b/drivers/hwtracing/coresight/coresight-syscfg.h
@@ -12,6 +12,17 @@
 
 #include "coresight-config.h"
 
+/*
+ * Load operation types.
+ * When loading or unloading, another load operation cannot be run.
+ * When unloading configurations cannot be activated.
+ */
+enum cscfg_load_ops {
+	CSCFG_NONE,
+	CSCFG_LOAD,
+	CSCFG_UNLOAD
+};
+
 /**
  * System configuration manager device.
  *
@@ -30,6 +41,7 @@
  * @cfgfs_subsys:	configfs subsystem used to manage configurations.
  * @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.
  */
 struct cscfg_manager {
 	struct device dev;
@@ -41,6 +53,7 @@ struct cscfg_manager {
 	struct configfs_subsystem cfgfs_subsys;
 	u32 sysfs_active_config;
 	int sysfs_active_preset;
+	enum cscfg_load_ops load_state;
 };
 
 /* get reference to dev in cscfg_manager */