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 12:07:46 -0600

On Tue, Jul 20, 2021 at 11:41:06AM -0600, Mathieu Poirier wrote:
> 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.  

I just read the rational for the above in the change summary...  I will have to
think further on this - more comments tomorrow.

> 
> 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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