Re: [PATCH v4 05/10] coresight: syscfg: Add API to activate and enable configurations

Hi Suzuki,

On Thu, 4 Mar 2021 at 16:49, Suzuki K Poulose [off-list ref] wrote:

On 1/28/21 5:09 PM, Mike Leach wrote:

quoted

Configurations are first activated, then when any coresight device is
enabled, the active configurations are checked and any matching
one is enabled.

This patch provides the activation / enable API.

Signed-off-by: Mike Leach <redacted>
---
  .../hwtracing/coresight/coresight-config.h    |   2 +
  .../hwtracing/coresight/coresight-syscfg.c    | 127 ++++++++++++++++++
  .../hwtracing/coresight/coresight-syscfg.h    |  10 +-
  include/linux/coresight.h                     |   2 +
  4 files changed, 140 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
index 98380b496046..26396b70c826 100644
--- a/drivers/hwtracing/coresight/coresight-config.h
+++ b/drivers/hwtracing/coresight/coresight-config.h

@@ -156,6 +156,7 @@ struct cscfg_config_feat_ref {
   * @presets:        Array of preset values.
   * @id_ea:  Extended attribute for perf configid value
   * @event_ea:       Extended attribute for perf event value
+ * @active_cnt: ref count for activate on this configuration.
   */
  struct cscfg_config_desc {
      const char *name;

@@ -168,6 +169,7 @@ struct cscfg_config_desc {
      const u64 *presets; /* nr_presets * nr_total_params */
      struct dev_ext_attribute *id_ea;
      struct dev_ext_attribute *event_ea;
+     atomic_t active_cnt;
  };

  /**

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
index a070f135eca3..d79cf5b36758 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg.c

@@ -298,6 +298,7 @@ static int cscfg_load_config(struct cscfg_config_desc *cfg_desc)
              return err;

      list_add(&cfg_desc->item, &cscfg_mgr->data.config_desc_list);
+     atomic_set(&cfg_desc->active_cnt, 0);
      return 0;
  }

@@ -477,6 +478,131 @@ void cscfg_unregister_csdev(struct coresight_device *csdev)
  }
  EXPORT_SYMBOL_GPL(cscfg_unregister_csdev);

+void cscfg_csdev_reset_feats(struct coresight_device *csdev)
+{
+     struct cscfg_feature_csdev *feat;
+
+     mutex_lock(&cscfg_csdev_mutex);
+     if (list_empty(&csdev->feature_csdev_list))
+             goto unlock_exit;
+
+     list_for_each_entry(feat, &csdev->feature_csdev_list, node)
+             cscfg_reset_feat(feat);
+
+unlock_exit:
+     mutex_unlock(&cscfg_csdev_mutex);
+}
+EXPORT_SYMBOL_GPL(cscfg_csdev_reset_feats);
+
+/**
+ * Mark a config descriptor as active.
+ * This will be seen when csdev devices are activated in the system.
+ *
+ * Selection by hash value - generated from the configuration name when it
+ * was loaded and added to the cs_etm/configurations file system for selection
+ * by perf.
+ *
+ * @cfg_hash: Hash value of the selected configuration name.
+ */
+int cscfg_activate_config(unsigned long cfg_hash)
+{
+     struct cscfg_config_desc *curr_item, *match_item = 0;

nit: s/0/NULL

OK.

quoted

+
+     mutex_lock(&cscfg_mutex);
+
+     list_for_each_entry(curr_item, &cscfg_mgr->data.config_desc_list, item) {
+             if ((unsigned long)curr_item->id_ea->var == cfg_hash) {
+                     match_item = curr_item;
+                     atomic_inc(&cscfg_mgr->data.sys_active_cnt);
+                     break;
+             }
+     }
+     mutex_unlock(&cscfg_mutex);
+
+     if (!match_item)
+             return -EINVAL;
+
+     dev_dbg(to_device_cscfg(), "Activate config %s.\n", match_item->name);
+
+     /* mark the descriptors as active so enable config will use them */
+     mutex_lock(&cscfg_csdev_mutex);
+     atomic_inc(&match_item->active_cnt);
+     mutex_unlock(&cscfg_csdev_mutex);

Is there a guarantee that this item is active and present in the list after
we dropped the mutex above ? We could certainly nest the mutex as long as
we follow the order everywhere to prevent such a race.

Although removal not supported in this set, the rule is that nothing
can be removed while any configuration is active (count on
sys_active_cnt). - but a comment here could be added.
That said, given this is an atomic, not sure that the mutex is
necessary (I think previous versions did more than just update the
count), & perhaps the increment should be moved to the main
list_for_each loop.

quoted

+
+     return 0;
+}
+EXPORT_SYMBOL_GPL(cscfg_activate_config);
+
+void cscfg_deactivate_config(unsigned long cfg_hash)
+{
+     struct cscfg_config_desc *curr_item, *match_item = 0;
+
+     mutex_lock(&cscfg_mutex);
+
+     list_for_each_entry(curr_item, &cscfg_mgr->data.config_desc_list, item) {
+             if ((unsigned long)curr_item->id_ea->var == cfg_hash) {
+                     match_item = curr_item;
+                     break;
+             }
+     }
+     mutex_unlock(&cscfg_mutex);
+     if (!match_item)
+             return;
+
+     dev_dbg(to_device_cscfg(), "Deactivate config %s.\n", match_item->name);
+
+     mutex_lock(&cscfg_csdev_mutex);
+     atomic_dec(&match_item->active_cnt);
+     mutex_unlock(&cscfg_csdev_mutex);
+
+     atomic_dec(&cscfg_mgr->data.sys_active_cnt);
+}
+EXPORT_SYMBOL_GPL(cscfg_deactivate_config);
+
+/* Find and program any active config for the supplied device.*/
+int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
+                                  unsigned long id_hash, int preset)
+{
+     struct cscfg_config_csdev *cfg = NULL, *item;
+     const struct cscfg_config_desc *desc;
+     int err = 0;
+
+     /* quickly check global count */
+     if (!atomic_read(&cscfg_mgr->data.sys_active_cnt))
+             return 0;
+
+     mutex_lock(&cscfg_csdev_mutex);
+     list_for_each_entry(item, &csdev->config_csdev_list, node) {
+             desc = item->desc;
+             if ((atomic_read(&desc->active_cnt)) &&
+                 ((unsigned long)desc->id_ea->var == id_hash)) {
+                     cfg = item;
+                     break;
+             }
+     }
+     if (cfg) {
+             err = cscfg_csdev_enable_config(cfg, preset);
+             if (!err)
+                     csdev->active_cfg_ctxt = (void *)cfg;
+     }
+     mutex_unlock(&cscfg_csdev_mutex);
+     return err;
+}
+EXPORT_SYMBOL_GPL(cscfg_csdev_enable_active_config);
+
+/* save and disable the active config for the device */
+void cscfg_csdev_disable_active_config(struct coresight_device *csdev)
+{
+     struct cscfg_config_csdev *cfg;
+
+     mutex_lock(&cscfg_csdev_mutex);
+     cfg = (struct cscfg_config_csdev *)csdev->active_cfg_ctxt;
+     if (cfg)
+             cscfg_csdev_disable_config(cfg);
+     mutex_unlock(&cscfg_csdev_mutex);
+}
+EXPORT_SYMBOL_GPL(cscfg_csdev_disable_active_config);
+
  /* Initialise system configuration management device. */

  struct device *to_device_cscfg(void)

@@ -546,6 +672,7 @@ int __init cscfg_init(void)
      INIT_LIST_HEAD(&cscfg_mgr->data.feat_desc_list);
      INIT_LIST_HEAD(&cscfg_mgr->data.config_desc_list);
      cscfg_mgr->data.nr_csdev = 0;
+     atomic_set(&cscfg_mgr->data.sys_active_cnt, 0);

      dev_info(to_device_cscfg(), "CoreSight Configuration manager initialised");
      return 0;

diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
index ebf5e1491d86..301e26e1e98f 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg.h
+++ b/drivers/hwtracing/coresight/coresight-syscfg.h

@@ -17,13 +17,15 @@
   * @csdev_list:             List of coresight devices registered with the configuration manager.
   * @feat_desc_list: List of feature descriptors to load into registered devices.

nit: Is this aligned ? (It is from Patch 1, though).

quoted

   * @config_desc_list:       List of system configuration descriptors to load into registered devices.
- * @nr_csdev:        Number of registered devices with the cscfg system
+ * @nr_csdev:                Number of registered devices with the cscfg system

Spurious change ?

This struct disappears in the v5 respin, so the comments will too.

quoted

+ * @sys_active_cnt:  Total number of active config descriptor references.
   */
  struct cscfg_api_data {
      struct list_head csdev_desc_list;
      struct list_head feat_desc_list;
      struct list_head config_desc_list;
      int nr_csdev;
+     atomic_t sys_active_cnt;
  };

  /**

@@ -53,6 +55,12 @@ int cscfg_register_csdev(struct coresight_device *csdev,
                       struct cscfg_match_desc *info,
                       struct cscfg_csdev_feat_ops *ops);
  void cscfg_unregister_csdev(struct coresight_device *csdev);
+int cscfg_activate_config(unsigned long cfg_hash);
+void cscfg_deactivate_config(unsigned long cfg_hash);
+void cscfg_csdev_reset_feats(struct coresight_device *csdev);
+int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
+                                  unsigned long id_hash, int preset);
+void cscfg_csdev_disable_active_config(struct coresight_device *csdev);

  /**
   * System configuration manager device.

diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index d0126ed326a6..3941854e8280 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h

@@ -221,6 +221,7 @@ struct coresight_sysfs_link {
   * @has_conns_grp: Have added a "connections" group for sysfs links.
   * @feature_csdev_list: List of complex feature programming added to the device.
   * @config_csdev_list:  List of system configurations added to the device.
+ * @active_cfg_ctxt:    Context information for current active congfig.
   */
  struct coresight_device {
      struct coresight_platform_data *pdata;

@@ -245,6 +246,7 @@ struct coresight_device {
      /* system configuration and feature lists */
      struct list_head feature_csdev_list;
      struct list_head config_csdev_list;
+     void *active_cfg_ctxt;
  };

Suzuki

Thanks for the review.

Mike
-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

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