Message-ID: <20210225212050.GA3567106@xps15>
Date:   Thu, 25 Feb 2021 14:20:50 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        linux-doc@...r.kernel.org, suzuki.poulose@....com,
        yabinc@...gle.com, corbet@....net, leo.yan@...aro.org,
        alexander.shishkin@...ux.intel.com, tingwei@...eaurora.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 05/10] coresight: syscfg: Add API to activate and
 enable configurations

On Thu, Jan 28, 2021 at 05:09:31PM +0000, Mike Leach wrote:
> 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 <mike.leach@...aro.org>
> ---
>  .../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;
> +
> +	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);

It would be nice to have a comment that mentions why this is needed.  I had to
go look in patch 09 to see that it prevents a feature from being changed when
any configuration is active.  And since patch 09 is the only place where
@sys_active_cnt is used, please move the declaration and handling of the
variable there.

> +			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);

What is ->active_cnt used for?  I see it referenced in
cscfg_csdev_enable_active_config() but it doesn't do much other than to confirm
the configuration has been activated by someone.  

There is also a chance that a caller would call cscfg_activate_config() once and
call cscfg_csdev_enable_active_config() multiple time, which would really create
problems.  I would move the incrementation of sys_active_cnt within the mutex
hold in cscfg_csdev_enable_active_config() and get rid of ->active_cnt.  If I am
correct we wouldn't need cscfg_activate_config() after that.

> +	mutex_unlock(&cscfg_csdev_mutex);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(cscfg_activate_config);
> +
> +void cscfg_deactivate_config(unsigned long cfg_hash)

I'm fine with either cfg_hash or id_hash, but not both.

> +{
> +	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.
>   * @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
> + * @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;
>  };
>  
>  /*
> -- 
> 2.17.1
> 

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