Subject: Re: [PATCH v8 05/10] coresight: syscfg: Add API to activate and enable configurations

From: Mathieu Poirier <[email-masked]>
Date: Tue, 20 Jul 2021 11:41:06 -0600

On Wed, Jul 07, 2021 at 02:29:58PM +0100, 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 <[email-masked]>
> Reviewed-by: Mathieu Poirier <[email-masked]>
> ---
>  .../hwtracing/coresight/coresight-config.h    |   2 +
>  .../hwtracing/coresight/coresight-syscfg.c    | 197 ++++++++++++++++++
>  .../hwtracing/coresight/coresight-syscfg.h    |   8 +
>  include/linux/coresight.h                     |   4 +
>  4 files changed, 211 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
> index 0667581822c1..25eb6c632692 100644
> --- a/drivers/hwtracing/coresight/coresight-config.h
> +++ b/drivers/hwtracing/coresight/coresight-config.h
> @@ -127,6 +127,7 @@ struct cscfg_feature_desc {
>   * @nr_total_params:	Sum of all parameters declared by used features
>   * @presets:		Array of preset values.
>   * @event_ea:		Extended attribute for perf event value
> + * @active_cnt:		ref count for activate on this configuration.
>   *
>   */
>  struct cscfg_config_desc {
> @@ -139,6 +140,7 @@ struct cscfg_config_desc {
>  	int nr_total_params;
>  	const u64 *presets; /* nr_presets * nr_total_params */
>  	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 b93f2b4a777e..4e9804875a9b 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -282,6 +282,7 @@ static int cscfg_load_config(struct cscfg_config_desc *config_desc)
>  		return err;
>  
>  	list_add(&config_desc->item, &cscfg_mgr->config_desc_list);
> +	atomic_set(&config_desc->active_cnt, 0);
>  	return 0;
>  }
>  
> @@ -468,6 +469,201 @@ void cscfg_unregister_csdev(struct coresight_device *csdev)
>  }
>  EXPORT_SYMBOL_GPL(cscfg_unregister_csdev);
>  
> +/**
> + * cscfg_csdev_reset_feats - reset features for a CoreSight device.
> + *
> + * Resets all parameters and register values for any features loaded
> + * into @csdev to their default values.
> + *
> + * @csdev: The CoreSight device.
> + */
> +void cscfg_csdev_reset_feats(struct coresight_device *csdev)
> +{
> +	struct cscfg_feature_csdev *feat_csdev;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&csdev->cscfg_csdev_lock, flags);
> +	if (list_empty(&csdev->feature_csdev_list))
> +		goto unlock_exit;
> +
> +	list_for_each_entry(feat_csdev, &csdev->feature_csdev_list, node)
> +		cscfg_reset_feat(feat_csdev);
> +
> +unlock_exit:
> +	spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
> +}
> +EXPORT_SYMBOL_GPL(cscfg_csdev_reset_feats);
> +
> +/**
> + * cscfg_activate_config -  Mark a configuration descriptor as active.
> + *
> + * This will be seen when csdev devices are enabled in the system.
> + * Only activated configurations can be enabled on individual devices.
> + * Activation protects the configuration from alteration or removal while
> + * active.
> + *
> + * 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.
> + *
> + * Increments the configuration descriptor active count and the global active
> + * count.
> + *
> + * @cfg_hash: Hash value of the selected configuration name.
> + */
> +int cscfg_activate_config(unsigned long cfg_hash)
> +{
> +	struct cscfg_config_desc *config_desc;
> +	int err = -EINVAL;
> +
> +	mutex_lock(&cscfg_mutex);
> +
> +	list_for_each_entry(config_desc, &cscfg_mgr->config_desc_list, item) {
> +		if ((unsigned long)config_desc->event_ea->var == cfg_hash) {
> +			/*
> +			 * increment the global active count - control changes to
> +			 * active configurations
> +			 */
> +			atomic_inc(&cscfg_mgr->sys_active_cnt);
> +
> +			/*
> +			 * mark the descriptor as active so enable config on a
> +			 * device instance will use it
> +			 */
> +			atomic_inc(&config_desc->active_cnt);
> +
> +			err = 0;
> +			dev_dbg(cscfg_device(), "Activate config %s.\n", config_desc->name);
> +			break;
> +		}
> +	}
> +	mutex_unlock(&cscfg_mutex);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(cscfg_activate_config);
> +
> +/**
> + * cscfg_deactivate_config -  Mark a config descriptor as inactive.
> + *
> + * Decrement the configuration and global active counts.
> + *
> + * @cfg_hash: Hash value of the selected configuration name.
> + */
> +void cscfg_deactivate_config(unsigned long cfg_hash)
> +{
> +	struct cscfg_config_desc *config_desc;
> +
> +	mutex_lock(&cscfg_mutex);
> +
> +	list_for_each_entry(config_desc, &cscfg_mgr->config_desc_list, item) {
> +		if ((unsigned long)config_desc->event_ea->var == cfg_hash) {
> +			atomic_dec(&config_desc->active_cnt);
> +			atomic_dec(&cscfg_mgr->sys_active_cnt);
> +			dev_dbg(cscfg_device(), "Deactivate config %s.\n", config_desc->name);
> +			break;
> +		}
> +	}
> +	mutex_unlock(&cscfg_mutex);
> +}
> +EXPORT_SYMBOL_GPL(cscfg_deactivate_config);
> +
> +/**
> + * cscfg_csdev_enable_active_config - Enable matching active configuration for device.
> + *
> + * Enables the configuration selected by @cfg_hash if the configuration is supported
> + * on the device and has been activated.
> + *
> + * If active and supported the CoreSight device @csdev will be programmed with the
> + * configuration, using @preset parameters.
> + *
> + * Should be called before driver hardware enable for the requested device, prior to
> + * programming and enabling the physical hardware.
> + *
> + * @csdev:	CoreSight device to program.
> + * @cfg_hash:	Selector for the configuration.
> + * @preset:	Preset parameter values to use, 0 for current / default values.
> + */
> +int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
> +				     unsigned long cfg_hash, int preset)
> +{
> +	struct cscfg_config_csdev *config_csdev_active = NULL, *config_csdev_item;
> +	const struct cscfg_config_desc *config_desc;
> +	unsigned long flags;
> +	int err = 0;
> +
> +	/* quickly check global count */
> +	if (!atomic_read(&cscfg_mgr->sys_active_cnt))
> +		return 0;
> +
> +	/* look for matching config - set in_enable flag if found */
> +	spin_lock_irqsave(&csdev->cscfg_csdev_lock, flags);
> +	list_for_each_entry(config_csdev_item, &csdev->config_csdev_list, node) {
> +		config_desc = config_csdev_item->config_desc;
> +		if ((atomic_read(&config_desc->active_cnt)) &&
> +		    ((unsigned long)config_desc->event_ea->var == cfg_hash)) {
> +			config_csdev_active = config_csdev_item;
> +			csdev->cscfg_in_enable = true;
> +			break;
> +		}
> +	}
> +	spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags)

In the previous revision the mutex wasn't dropped and
cscfg_csdev_enable_config() was called with the mutex held.  Any reason for not
doing that with the spinlock implemenation?  If anything it should be more
efficient because the spinlock is on a per csdev basis.  It would also keep
things simple and avoid adding a new ->cscfg_in_enable field to the
coresight_device structure.  That last point really concerns me - if holding the
spinlock is not possible than a new approach should be considered.  

Thanks,
Mathieu

> +
> +	/*
> +	 * If found, attempt to enable and then set as enabled if no error
> +	 * and in enable flag still set.
> +	 */
> +	if (config_csdev_active) {
> +		/*
> +		 * Call the generic routine that will program up the internal
> +		 * driver structures prior to programming up the hardware.
> +		 * This routine takes the driver spinlock saved in the configs.
> +		 */
> +		err = cscfg_csdev_enable_config(config_csdev_active, preset);
> +		if (!err) {
> +			/*
> +			 * Successful programming. re-check in_enable flag
> +			 * to avoid potential race with disable config.
> +			 */
> +			spin_lock_irqsave(&csdev->cscfg_csdev_lock, flags);
> +			if (csdev->cscfg_in_enable)
> +				csdev->active_cscfg_ctxt = (void *)config_csdev_active;
> +			csdev->cscfg_in_enable = false;
> +			spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
> +		}
> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(cscfg_csdev_enable_active_config);
> +
> +/**
> + * cscfg_csdev_disable_active_config - disable an active config on the device.
> + *
> + * Disables the active configuration on the CoreSight device @csdev.
> + * Disable will save the values of any registers marked in the configurations
> + * as save on disable.
> + *
> + * Should be called after driver hardware disable for the requested device,
> + * after disabling the physical hardware and reading back registers.
> + *
> + * @csdev: The CoreSight device.
> + */
> +void cscfg_csdev_disable_active_config(struct coresight_device *csdev)
> +{
> +	struct cscfg_config_csdev *config_csdev;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&csdev->cscfg_csdev_lock, flags);
> +	csdev->cscfg_in_enable = false;
> +	config_csdev = (struct cscfg_config_csdev *)csdev->active_cscfg_ctxt;
> +	csdev->active_cscfg_ctxt = NULL;
> +	spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
> +
> +	if (config_csdev)
> +		cscfg_csdev_disable_config(config_csdev);
> +}
> +EXPORT_SYMBOL_GPL(cscfg_csdev_disable_active_config);
> +
>  /* Initialise system configuration management device. */
>  
>  struct device *cscfg_device(void)
> @@ -536,6 +732,7 @@ int __init cscfg_init(void)
>  	INIT_LIST_HEAD(&cscfg_mgr->csdev_desc_list);
>  	INIT_LIST_HEAD(&cscfg_mgr->feat_desc_list);
>  	INIT_LIST_HEAD(&cscfg_mgr->config_desc_list);
> +	atomic_set(&cscfg_mgr->sys_active_cnt, 0);
>  
>  	dev_info(cscfg_device(), "CoreSight Configuration manager initialised");
>  	return 0;
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
> index 5bcae3b374c6..a52775890670 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.h
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.h
> @@ -24,12 +24,14 @@
>   * @csdev_desc_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.
> + * @sys_active_cnt:	Total number of active config descriptor references.
>   */
>  struct cscfg_manager {
>  	struct device dev;
>  	struct list_head csdev_desc_list;
>  	struct list_head feat_desc_list;
>  	struct list_head config_desc_list;
> +	atomic_t sys_active_cnt;
>  };
>  
>  /* get reference to dev in cscfg_manager */
> @@ -61,5 +63,11 @@ int cscfg_load_config_sets(struct cscfg_config_desc **cfg_descs,
>  int cscfg_register_csdev(struct coresight_device *csdev, u32 match_flags,
>  			 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 cfg_hash, int preset);
> +void cscfg_csdev_disable_active_config(struct coresight_device *csdev);
>  
>  #endif /* CORESIGHT_SYSCFG_H */
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index 16544ae2b532..e66e1a5fd803 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -223,6 +223,8 @@ struct coresight_sysfs_link {
>   * @feature_csdev_list: List of complex feature programming added to the device.
>   * @config_csdev_list:  List of system configurations added to the device.
>   * @cscfg_csdev_lock:	Protect the lists of configurations and features.
> + * @active_cscfg_ctxt:  Context information for current active system configuration.
> + * @cscfg_in_enable:    Flag to indicate we are in the process of enabling.
>   */
>  struct coresight_device {
>  	struct coresight_platform_data *pdata;
> @@ -248,6 +250,8 @@ struct coresight_device {
>  	struct list_head feature_csdev_list;
>  	struct list_head config_csdev_list;
>  	spinlock_t cscfg_csdev_lock;
> +	void *active_cscfg_ctxt;
> +	bool cscfg_in_enable;
>  };
>  
>  /*
> -- 
> 2.17.1
> 

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