Date:   Sun, 28 Feb 2021 17:04:25 -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 09/10] coresight: syscfg: Add initial configfs support

On Sun, Feb 28, 2021 at 05:02:28PM -0700, Mathieu Poirier wrote:
> On Thu, Jan 28, 2021 at 05:09:35PM +0000, Mike Leach wrote:
> > Adds configfs subsystem and attributes to the configuration manager
> > to enable the listing of loaded configurations and features.
> > 
> > The default values of feature parameters can be accessed and altered
> > from these attributes to affect all installed devices using the feature.
> > 
> > Signed-off-by: Mike Leach <mike.leach@...aro.org>

I get the following warning when applying this patch:

Applying: coresight: syscfg: Add initial configfs support
.git/rebase-apply/patch:34: new blank line at EOF.
+
warning: 1 line adds whitespace errors.

Please address.

> > ---
> >  drivers/hwtracing/coresight/Makefile          |   3 +-
> >  .../hwtracing/coresight/coresight-config.c    |   1 +
> >  .../coresight/coresight-syscfg-configfs.c     | 399 ++++++++++++++++++
> >  .../coresight/coresight-syscfg-configfs.h     |  45 ++
> >  .../hwtracing/coresight/coresight-syscfg.c    |  77 ++++
> >  .../hwtracing/coresight/coresight-syscfg.h    |   7 +
> >  6 files changed, 531 insertions(+), 1 deletion(-)
> >  create mode 100644 drivers/hwtracing/coresight/coresight-syscfg-configfs.c
> >  create mode 100644 drivers/hwtracing/coresight/coresight-syscfg-configfs.h
> > 
> > diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> > index 2707bfef1b76..391c93a08902 100644
> > --- a/drivers/hwtracing/coresight/Makefile
> > +++ b/drivers/hwtracing/coresight/Makefile
> > @@ -5,7 +5,8 @@
> >  obj-$(CONFIG_CORESIGHT) += coresight.o
> >  coresight-y := coresight-core.o  coresight-etm-perf.o coresight-platform.o \
> >  		coresight-sysfs.o coresight-syscfg.o coresight-config.o \
> > -		coresight-cfg-preload.o coresight-cfg-afdo.o
> > +		coresight-cfg-preload.o coresight-cfg-afdo.o \
> > +		coresight-syscfg-configfs.o
> >  obj-$(CONFIG_CORESIGHT_LINK_AND_SINK_TMC) += coresight-tmc.o
> >  coresight-tmc-y := coresight-tmc-core.o coresight-tmc-etf.o \
> >  		      coresight-tmc-etr.o
> > diff --git a/drivers/hwtracing/coresight/coresight-config.c b/drivers/hwtracing/coresight/coresight-config.c
> > index 6cc4b213d9b6..225ceca1428c 100644
> > --- a/drivers/hwtracing/coresight/coresight-config.c
> > +++ b/drivers/hwtracing/coresight/coresight-config.c
> > @@ -243,3 +243,4 @@ void cscfg_csdev_disable_config(struct cscfg_config_csdev *cfg)
> >  		cfg->enabled = false;
> >  	}
> >  }
> > +
> 
> Spurious change
> 
> > diff --git a/drivers/hwtracing/coresight/coresight-syscfg-configfs.c b/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
> > new file mode 100644
> > index 000000000000..79a11ebd6782
> > --- /dev/null
> > +++ b/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
> > @@ -0,0 +1,399 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2020 Linaro Limited, All rights reserved.
> > + * Author: Mike Leach <mike.leach@...aro.org>
> > + */
> > +
> > +#include <linux/configfs.h>
> > +
> > +#include "coresight-syscfg-configfs.h"
> > +
> > +/* create a default ci_type. */
> > +static inline struct config_item_type *cscfg_create_ci_type(void)
> > +{
> > +	struct config_item_type *ci_type;
> > +
> > +	ci_type = devm_kzalloc(to_device_cscfg(), sizeof(*ci_type), GFP_KERNEL);
> > +	if (ci_type)
> > +		ci_type->ct_owner = THIS_MODULE;
> > +
> > +	return ci_type;
> > +}
> > +
> > +/* configurations sub-group */
> > +
> > +/* attributes for the config view group */
> > +static ssize_t cscfg_cfg_description_show(struct config_item *item, char *page)
> > +{
> > +	struct cscfg_fs_config *fs_config = container_of(to_config_group(item),
> > +							 struct cscfg_fs_config, group);
> > +
> > +	return scnprintf(page, PAGE_SIZE, "%s\n", fs_config->desc->brief);
> > +}
> > +CONFIGFS_ATTR_RO(cscfg_cfg_, description);
> > +
> > +static ssize_t cscfg_cfg_feature_refs_show(struct config_item *item, char *page)
> > +{
> > +	struct cscfg_fs_config *fs_config = container_of(to_config_group(item),
> > +							 struct cscfg_fs_config, group);
> > +	const struct cscfg_config_desc *desc = fs_config->desc;
> > +	ssize_t ch_used = 0;
> > +	int i;
> > +
> > +	if (desc->nr_refs) {
> > +		for (i = 0; i < desc->nr_refs; i++) {
> > +			ch_used += scnprintf(page + ch_used, PAGE_SIZE - ch_used,
> > +					     "%s\n", desc->refs[i].name);
> > +		}
> > +	}
> > +	return ch_used;
> > +}
> > +CONFIGFS_ATTR_RO(cscfg_cfg_, feature_refs);
> > +
> > +/* list preset values in order of features and params */
> > +static ssize_t cscfg_cfg_values_show(struct config_item *item, char *page)
> > +{
> > +	const struct cscfg_feature_desc *feat;
> > +	const struct cscfg_config_desc *cfg;
> > +	struct cscfg_fs_preset *fs_preset;
> > +	int i, j, val_idx, preset_idx;
> > +	ssize_t used = 0;
> > +
> > +	fs_preset = container_of(to_config_group(item), struct cscfg_fs_preset, group);
> > +	cfg = fs_preset->desc;
> > +
> > +	if (!cfg->nr_presets)
> > +		return 0;
> > +
> > +	preset_idx = fs_preset->preset_num - 1;
> > +
> > +	/* start index on the correct array line */
> > +	val_idx = cfg->nr_total_params * preset_idx;
> > +
> > +	/*
> > +	 * A set of presets is the sum of all params in used features,
> > +	 * in order of declaration of features and params in the features
> > +	 */
> > +	for (i = 0; i < cfg->nr_refs; i++) {
> > +		feat = cscfg_get_named_feat_desc(cfg->refs[i].name);
> > +		for (j = 0; j < feat->nr_params; j++) {
> > +			used += scnprintf(page + used, PAGE_SIZE - used,
> > +					  "%s.%s = 0x%llx ",
> > +					  feat->name, feat->params[j].name,
> > +					  cfg->presets[val_idx++]);
> > +		}
> > +	}
> > +	used += scnprintf(page + used, PAGE_SIZE - used, "\n");
> > +
> > +	return used;
> > +}
> > +CONFIGFS_ATTR_RO(cscfg_cfg_, values);
> > +
> > +static struct configfs_attribute *cscfg_config_view_attrs[] = {
> > +	&cscfg_cfg_attr_description,
> > +	&cscfg_cfg_attr_feature_refs,
> > +	NULL,
> > +};
> > +
> > +static struct config_item_type cscfg_config_view_type = {
> > +	.ct_owner = THIS_MODULE,
> > +	.ct_attrs = cscfg_config_view_attrs,
> > +};
> > +
> > +static struct configfs_attribute *cscfg_config_preset_attrs[] = {
> > +	&cscfg_cfg_attr_values,
> > +	NULL,
> > +};
> > +
> > +static struct config_item_type cscfg_config_preset_type = {
> > +	.ct_owner = THIS_MODULE,
> > +	.ct_attrs = cscfg_config_preset_attrs,
> > +};
> > +
> > +
> 
> Extra line
> 
> > +static int cscfg_add_preset_groups(struct cscfg_fs_config *cfg_view)
> > +{
> > +	int preset_num;
> > +	struct cscfg_fs_preset *cfg_preset;
> > +	struct cscfg_config_desc *cfg_desc = cfg_view->desc;
> > +	char name[CONFIGFS_ITEM_NAME_LEN];
> > +
> > +	if (!cfg_desc->nr_presets)
> > +		return 0;
> > +
> > +	for (preset_num = 1; preset_num <= cfg_desc->nr_presets; preset_num++) {
> > +		cfg_preset = devm_kzalloc(to_device_cscfg(),
> > +					  sizeof(struct cscfg_fs_config), GFP_KERNEL);
> > +
> > +		if (!cfg_preset)
> > +			return -ENOMEM;
> > +
> > +		snprintf(name, CONFIGFS_ITEM_NAME_LEN, "preset%d", preset_num);
> > +		cfg_preset->preset_num = preset_num;
> > +		cfg_preset->desc = cfg_view->desc;
> > +		config_group_init_type_name(&cfg_preset->group, name,
> > +					    &cscfg_config_preset_type);
> > +		configfs_add_default_group(&cfg_preset->group, &cfg_view->group);
> > +	}
> > +	return 0;
> > +}
> > +
> > +static struct config_group *cscfg_create_config_group(struct cscfg_config_desc *cfg_desc)
> > +{
> > +	struct cscfg_fs_config *cfg_view;
> > +	struct device *dev = to_device_cscfg();
> > +	int err;
> > +
> > +	if (!dev)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	cfg_view = devm_kzalloc(dev, sizeof(struct cscfg_fs_config), GFP_KERNEL);
> > +	if (!cfg_view)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	cfg_view->desc = cfg_desc;
> > +	config_group_init_type_name(&cfg_view->group, cfg_desc->name, &cscfg_config_view_type);
> > +
> > +	/* add in a preset<n> dir for each preset */
> > +	err = cscfg_add_preset_groups(cfg_view);
> > +	if (err)
> > +		return ERR_PTR(err);
> > +
> > +	return &cfg_view->group;
> > +}
> > +
> > +/* attributes for features view */
> > +
> > +static ssize_t cscfg_feat_description_show(struct config_item *item, char *page)
> > +{
> > +	struct cscfg_fs_feature *fs_feat = container_of(to_config_group(item),
> > +							struct cscfg_fs_feature, group);
> > +
> > +	return scnprintf(page, PAGE_SIZE, "%s\n", fs_feat->desc->brief);
> > +}
> > +CONFIGFS_ATTR_RO(cscfg_feat_, description);
> > +
> > +static ssize_t cscfg_feat_matches_show(struct config_item *item, char *page)
> > +{
> > +	struct cscfg_fs_feature *fs_feat = container_of(to_config_group(item),
> > +							struct cscfg_fs_feature, group);
> > +	u32 match_flags = fs_feat->desc->match_flags;
> > +	int used = 0;
> > +
> > +	if (match_flags & CS_CFG_MATCH_CLASS_SRC_ALL)
> > +		used = scnprintf(page, PAGE_SIZE, "SRC_ALL ");
> > +
> > +	if (match_flags & CS_CFG_MATCH_CLASS_SRC_ETM4)
> > +		used += scnprintf(page + used, PAGE_SIZE - used, "SRC_ETMV4 ");
> > +
> > +	used += scnprintf(page + used, PAGE_SIZE - used, "\n");
> > +	return used;
> > +}
> > +CONFIGFS_ATTR_RO(cscfg_feat_, matches);
> > +
> > +static ssize_t cscfg_feat_nr_params_show(struct config_item *item, char *page)
> > +{
> > +	struct cscfg_fs_feature *fs_feat = container_of(to_config_group(item),
> > +							struct cscfg_fs_feature, group);
> > +
> > +	return scnprintf(page, PAGE_SIZE, "%d\n", fs_feat->desc->nr_params);
> > +}
> > +CONFIGFS_ATTR_RO(cscfg_feat_, nr_params);
> > +
> > +/* base feature desc attrib structures */
> > +static struct configfs_attribute *cscfg_feature_view_attrs[] = {
> > +	&cscfg_feat_attr_description,
> > +	&cscfg_feat_attr_matches,
> > +	&cscfg_feat_attr_nr_params,
> > +	NULL,
> > +};
> > +
> > +static struct config_item_type cscfg_feature_view_type = {
> > +	.ct_owner = THIS_MODULE,
> > +	.ct_attrs = cscfg_feature_view_attrs,
> > +};
> > +
> > +static ssize_t cscfg_param_value_show(struct config_item *item, char *page)
> > +{
> > +	struct cscfg_fs_param *param_item = container_of(to_config_group(item),
> > +							 struct cscfg_fs_param, group);
> > +	int param_idx = param_item->param_idx;
> > +	struct cscfg_feature_desc *desc = param_item->desc;
> > +
> > +	return scnprintf(page, PAGE_SIZE, "0x%llx\n", desc->params[param_idx].value);
> > +}
> > +
> > +static ssize_t cscfg_param_value_store(struct config_item *item,
> > +				       const char *page, size_t size)
> > +{
> > +	struct cscfg_fs_param *param_item = container_of(to_config_group(item),
> > +							 struct cscfg_fs_param, group);
> > +	struct cscfg_feature_desc *desc = param_item->desc;
> > +	int param_idx = param_item->param_idx;
> > +	u64 val;
> > +	int err;
> > +
> > +	err = kstrtoull(page, 0, &val);
> > +	if (!err)
> > +		err = cscfg_update_feat_param_val(desc, param_idx, val);
> > +
> > +	return err ? err : size;
> > +}
> > +CONFIGFS_ATTR(cscfg_param_, value);
> > +
> > +static struct configfs_attribute *cscfg_param_view_attrs[] = {
> > +	&cscfg_param_attr_value,
> > +	NULL,
> > +};
> > +
> > +static struct config_item_type cscfg_param_view_type = {
> > +	.ct_owner = THIS_MODULE,
> > +	.ct_attrs = cscfg_param_view_attrs,
> > +};
> > +
> > +/*
> > + * configfs has far less functionality provided to add attributes dynamically than sysfs,
> > + * and the show and store fns pass the enclosing config_item so the actual attribute cannot
> > + * be determined. Therefore we add each item as a group directory, with a value attribute.
> > + */
> > +static int cscfg_create_params_group_items(struct cscfg_feature_desc *feat_desc,
> > +					   struct config_group *params_group)
> > +{
> > +	struct device *dev = to_device_cscfg();
> > +	struct cscfg_fs_param *param_item;
> > +	int i;
> > +
> > +	/* parameter items - as groups with default_value attribute */
> > +	for (i = 0; i < feat_desc->nr_params; i++) {
> > +		param_item = devm_kzalloc(dev, sizeof(struct cscfg_fs_param), GFP_KERNEL);
> > +		if (!param_item)
> > +			return -ENOMEM;
> > +		param_item->desc = feat_desc;
> > +		param_item->param_idx = i;
> > +		config_group_init_type_name(&param_item->group, feat_desc->params[i].name,
> > +					    &cscfg_param_view_type);
> > +		configfs_add_default_group(&param_item->group, params_group);
> > +	}
> > +	return 0;
> > +}
> > +
> > +static struct config_group *cscfg_create_feature_group(struct cscfg_feature_desc *feat_desc)
> > +{
> > +	struct cscfg_fs_feature *feat_view;
> > +	struct config_item_type *params_group_type;
> > +	struct config_group *params_group = NULL;
> > +	struct device *dev = to_device_cscfg();
> > +	int item_err;
> > +
> > +	if (!dev)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	feat_view = devm_kzalloc(dev, sizeof(struct cscfg_fs_feature), GFP_KERNEL);
> > +	if (!feat_view)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	if (feat_desc->nr_params) {
> > +		params_group = devm_kzalloc(dev, sizeof(struct config_group), GFP_KERNEL);
> > +		if (!params_group)
> > +			return ERR_PTR(-ENOMEM);
> > +
> > +		params_group_type = cscfg_create_ci_type();
> > +		if (!params_group_type)
> > +			return ERR_PTR(-ENOMEM);
> > +	}
> > +
> > +	feat_view->desc = feat_desc;
> > +	config_group_init_type_name(&feat_view->group,
> > +				    feat_desc->name,
> > +				    &cscfg_feature_view_type);
> > +	if (params_group) {
> > +		config_group_init_type_name(params_group, "params", params_group_type);
> > +		configfs_add_default_group(params_group, &feat_view->group);
> > +		item_err = cscfg_create_params_group_items(feat_desc, params_group);
> > +		if (item_err)
> > +			return ERR_PTR(item_err);
> > +	}
> > +	return &feat_view->group;
> > +}
> > +
> > +static struct config_item_type cscfg_configs_type = {
> > +	.ct_owner = THIS_MODULE,
> > +};
> > +
> > +static struct config_group cscfg_configs_grp = {
> > +	.cg_item = {
> > +		.ci_namebuf = "configurations",
> > +		.ci_type = &cscfg_configs_type,
> > +	},
> > +};
> > +
> > +/* add configuration to configurations group */
> > +int cscfg_configfs_add_config(struct cscfg_config_desc *cfg_desc)
> > +{
> > +	struct config_group *new_group;
> > +	int err;
> > +
> > +	new_group = cscfg_create_config_group(cfg_desc);
> > +	if (IS_ERR(new_group))
> > +		return PTR_ERR(new_group);
> > +	err =  configfs_register_group(&cscfg_configs_grp, new_group);
> > +	return err;
> > +}
> > +
> > +static struct config_item_type cscfg_features_type = {
> > +	.ct_owner = THIS_MODULE,
> > +};
> > +
> > +static struct config_group cscfg_features_grp = {
> > +	.cg_item = {
> > +		.ci_namebuf = "features",
> > +		.ci_type = &cscfg_features_type,
> > +	},
> > +};
> > +
> > +/* add feature to features group */
> > +int cscfg_configfs_add_feature(struct cscfg_feature_desc *feat_desc)
> > +{
> > +	struct config_group *new_group;
> > +	int err;
> > +
> > +	new_group = cscfg_create_feature_group(feat_desc);
> > +	if (IS_ERR(new_group))
> > +		return PTR_ERR(new_group);
> > +	err =  configfs_register_group(&cscfg_features_grp, new_group);
> > +	return err;
> > +}
> > +
> > +int cscfg_configfs_init(struct cscfg_manager *cscfg_mgr)
> > +{
> > +	struct configfs_subsystem *subsys;
> > +	struct config_item_type *ci_type;
> > +
> > +	if (!cscfg_mgr)
> > +		return -EINVAL;
> > +
> > +	ci_type = cscfg_create_ci_type();
> > +	if (!ci_type)
> > +		return -ENOMEM;
> > +
> > +	subsys = &cscfg_mgr->cfgfs_subsys;
> > +	config_item_set_name(&subsys->su_group.cg_item, CSCFG_FS_SUBSYS_NAME);
> > +	subsys->su_group.cg_item.ci_type = ci_type;
> > +
> > +	config_group_init(&subsys->su_group);
> > +	mutex_init(&subsys->su_mutex);
> > +
> > +	/* Add default groups to subsystem */
> > +	config_group_init(&cscfg_configs_grp);
> > +	configfs_add_default_group(&cscfg_configs_grp, &subsys->su_group);
> > +
> > +	config_group_init(&cscfg_features_grp);
> > +	configfs_add_default_group(&cscfg_features_grp, &subsys->su_group);
> > +
> > +	return configfs_register_subsystem(subsys);
> > +}
> > +
> > +void cscfg_configfs_release(struct cscfg_manager *cscfg_mgr)
> > +{
> > +	configfs_unregister_subsystem(&cscfg_mgr->cfgfs_subsys);
> > +}
> > diff --git a/drivers/hwtracing/coresight/coresight-syscfg-configfs.h b/drivers/hwtracing/coresight/coresight-syscfg-configfs.h
> > new file mode 100644
> > index 000000000000..5e49819b80fc
> > --- /dev/null
> > +++ b/drivers/hwtracing/coresight/coresight-syscfg-configfs.h
> > @@ -0,0 +1,45 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +/*
> > + * Coresight system configuration driver - support for configfs.
> > + */
> > +
> > +#ifndef CORESIGHT_SYSCFG_CONFIGFS_H
> > +#define CORESIGHT_SYSCFG_CONFIGFS_H
> > +
> > +#include <linux/configfs.h>
> > +#include "coresight-syscfg.h"
> > +
> > +#define CSCFG_FS_SUBSYS_NAME "coresight-syscfg"
> 
> We have cs_etm under /sys/bus/events/device/.  Would it make sense to call this
> cs-syscfg?
> 
> > +
> > +/* container for configuration view */
> > +struct cscfg_fs_config {
> > +	struct cscfg_config_desc *desc;
> > +	struct config_group group;
> > +};
> > +
> > +/* container for feature view */
> > +struct cscfg_fs_feature {
> > +	struct cscfg_feature_desc *desc;
> > +	struct config_group group;
> > +};
> > +
> > +/* container for parameter view */
> > +struct cscfg_fs_param {
> > +	int param_idx;
> > +	struct cscfg_feature_desc *desc;
> > +	struct config_group group;
> > +};
> > +
> > +/* container for preset view */
> > +struct cscfg_fs_preset {
> > +	int preset_num;
> > +	struct cscfg_config_desc *desc;
> > +	struct config_group group;
> > +};
> > +
> > +int cscfg_configfs_init(struct cscfg_manager *cscfg_mgr);
> > +void cscfg_configfs_release(struct cscfg_manager *cscfg_mgr);
> > +int cscfg_configfs_add_config(struct cscfg_config_desc *cfg_desc);
> > +int cscfg_configfs_add_feature(struct cscfg_feature_desc *feat_desc);
> > +
> > +#endif /* CORESIGHT_SYSCFG_CONFIGFS_H */
> > diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> > index d79cf5b36758..c0707c31fc31 100644
> > --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> > +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> > @@ -9,6 +9,7 @@
> >  #include "coresight-config.h"
> >  #include "coresight-etm-perf.h"
> >  #include "coresight-syscfg.h"
> > +#include "coresight-syscfg-configfs.h"
> >  
> >  /*
> >   * cscfg_ API manages configurations and features for the entire coresight
> > @@ -302,6 +303,70 @@ static int cscfg_load_config(struct cscfg_config_desc *cfg_desc)
> >  	return 0;
> >  }
> >  
> > +/* get a feature descriptor by name */
> > +const struct cscfg_feature_desc *cscfg_get_named_feat_desc(const char *name)
> > +{
> > +	const struct cscfg_feature_desc *feat = NULL, *feat_item;
> > +
> > +	mutex_lock(&cscfg_mutex);
> > +
> > +	list_for_each_entry(feat_item, &cscfg_mgr->data.feat_desc_list, item) {
> > +		if (strcmp(feat_item->name, name) == 0) {
> > +			feat = feat_item;
> > +			break;
> > +		}
> > +	}
> > +
> > +	mutex_unlock(&cscfg_mutex);
> > +	return feat;
> > +}
> > +
> > +static struct cscfg_feature_csdev *
> > +cscfg_csdev_get_feat_from_desc(struct coresight_device *csdev,
> > +			       struct cscfg_feature_desc *feat_desc)
> > +{
> > +	struct cscfg_feature_csdev *feat_csdev = NULL, *item;
> > +
> > +	list_for_each_entry(item, &csdev->feature_csdev_list, node) {
> > +		if (item->desc == feat_desc) {
> > +			feat_csdev = item;
> > +			break;
> > +		}
> > +	}
> > +	return feat_csdev;
> > +}
> > +
> > +int cscfg_update_feat_param_val(struct cscfg_feature_desc *feat_desc,
> > +				int param_idx, u64 value)
> > +{
> > +	int err = 0;
> > +	struct cscfg_feature_csdev *feat_csdev;
> > +	struct cscfg_csdev_register *item;
> > +
> > +	mutex_lock(&cscfg_mutex);
> > +
> > +	/* check if any config active & return busy */
> > +	if (atomic_read(&cscfg_mgr->data.sys_active_cnt)) {
> > +		err = -EBUSY;
> > +		goto unlock_exit;
> > +	}
> > +
> > +	/* set the value */
> > +	feat_desc->params[param_idx].value = value;
> > +
> > +	/* update loaded instances.*/
> > +	list_for_each_entry(item, &cscfg_mgr->data.csdev_desc_list, item) {
> > +		feat_csdev = cscfg_csdev_get_feat_from_desc(item->csdev, feat_desc);
> > +		if (feat_csdev)
> > +			feat_csdev->params[param_idx].current_value = value;
> > +	}
> > +
> > +unlock_exit:
> > +	mutex_unlock(&cscfg_mutex);
> > +	return err;
> > +}
> > +
> > +
> 
> Extra line
> 
> >  /*
> >   * External API function to load feature and config sets.
> >   * Take a 0 terminated array of feature descriptors and/or configuration
> > @@ -324,6 +389,7 @@ int cscfg_load_config_sets(struct cscfg_config_desc **cfg_descs,
> >  				       feat_descs[i]->name);
> >  				goto do_unlock;
> >  			}
> > +			cscfg_configfs_add_feature(feat_descs[i]);
> >  			i++;
> >  		}
> >  	}
> > @@ -338,6 +404,7 @@ int cscfg_load_config_sets(struct cscfg_config_desc **cfg_descs,
> >  				       cfg_descs[i]->name);
> >  				goto do_unlock;
> >  			}
> > +			cscfg_configfs_add_config(cfg_descs[i]);
> >  			i++;
> >  		}
> >  	}
> > @@ -613,6 +680,7 @@ struct device *to_device_cscfg(void)
> >  /* Must have a release function or the kernel will complain on module unload */
> >  void cscfg_dev_release(struct device *dev)
> >  {
> > +	cscfg_configfs_release(cscfg_mgr);
> >  	kfree(cscfg_mgr);
> >  	cscfg_mgr = NULL;
> >  }
> > @@ -639,6 +707,7 @@ int cscfg_create_device(void)
> >  	dev->init_name = "system_cfg";
> >  
> >  	err = device_register(dev);
> > +
> 
> Extra line
> 
> I have run out of time for this patchset.  Please spin off another revision and
> we'll go from there.  
> 
> The core of the feature works and I think we should move forward with it.
> 
> Thanks,
> Mathieu
> 
> >  	if (err)
> >  		cscfg_dev_release(dev);
> >  
> > @@ -668,6 +737,10 @@ int __init cscfg_init(void)
> >  	if (err)
> >  		return err;
> >  
> > +	err = cscfg_configfs_init(cscfg_mgr);
> > +	if (err)
> > +		goto exit_dev_clear;
> > +
> >  	INIT_LIST_HEAD(&cscfg_mgr->data.csdev_desc_list);
> >  	INIT_LIST_HEAD(&cscfg_mgr->data.feat_desc_list);
> >  	INIT_LIST_HEAD(&cscfg_mgr->data.config_desc_list);
> > @@ -676,6 +749,10 @@ int __init cscfg_init(void)
> >  
> >  	dev_info(to_device_cscfg(), "CoreSight Configuration manager initialised");
> >  	return 0;
> > +
> > +exit_dev_clear:
> > +	cscfg_clear_device();
> > +	return err;
> >  }
> >  
> >  void __exit cscfg_exit(void)
> > diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
> > index a8a6b21315d8..62700e4e9e05 100644
> > --- a/drivers/hwtracing/coresight/coresight-syscfg.h
> > +++ b/drivers/hwtracing/coresight/coresight-syscfg.h
> > @@ -6,6 +6,7 @@
> >  #ifndef CORESIGHT_SYSCFG_H
> >  #define CORESIGHT_SYSCFG_H
> >  
> > +#include <linux/configfs.h>
> >  #include <linux/coresight.h>
> >  #include <linux/device.h>
> >  
> > @@ -48,6 +49,10 @@ struct cscfg_csdev_register {
> >  int __init cscfg_init(void);
> >  void __exit cscfg_exit(void);
> >  int cscfg_preload(void);
> > +const struct cscfg_feature_desc *cscfg_get_named_feat_desc(const char *name);
> > +int cscfg_update_feat_param_val(struct cscfg_feature_desc *feat_desc,
> > +				int param_idx, u64 value);
> > +
> >  
> >  /* syscfg manager external API */
> >  int cscfg_load_config_sets(struct cscfg_config_desc **cfg_descs,
> > @@ -71,10 +76,12 @@ void cscfg_csdev_disable_active_config(struct coresight_device *csdev);
> >   *
> >   * @dev:	The device.
> >   * @data:	The API data.
> > + * @cfgfs_subsys: configfs subsystem used to manage configurations.
> >   */
> >  struct cscfg_manager {
> >  	struct device dev;
> >  	struct cscfg_api_data data;
> > +	struct configfs_subsystem cfgfs_subsys;
> >  };
> >  
> >  /* get reference to dev in cscfg_manager */
> > -- 
> > 2.17.1
> > 

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