Date:   Tue, 26 May 2020 11:03:28 -0700
From:   rishabhb@...eaurora.org
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     linux-remoteproc@...r.kernel.org, ohad@...ery.com,
        linux-kernel@...r.kernel.org, tsoni@...eaurora.org,
        psodagud@...eaurora.org, sidgup@...eaurora.org
Subject: Re: [PATCH v3 1/2] remoteproc: qcom: Add per subsystem SSR
 notification

On 2020-05-19 13:38, Bjorn Andersson wrote:
> On Tue 28 Apr 15:16 PDT 2020, Rishabh Bhatnagar wrote:
> 
>> Currently there is a single notification chain which is called 
>> whenever any
>> remoteproc shuts down. This leads to all the listeners being notified, 
>> and
>> is not an optimal design as kernel drivers might only be interested in
>> listening to notifications from a particular remoteproc. Create a 
>> global
>> list of remoteproc notification info data structures. This will hold 
>> the
>> name and notifier_list information for a particular remoteproc. The 
>> API
>> to register for notifications will use name argument to retrieve the
>> notification info data structure and the notifier block will be added 
>> to
>> that data structure's notification chain.
>> 
>> Signed-off-by: Siddharth Gupta <sidgup@...eaurora.org>
>> Signed-off-by: Rishabh Bhatnagar <rishabhb@...eaurora.org>
> 
> Thanks Rishabh, design wise I think this looks good now, just some code
> style things below.
> 
>> ---
>>  drivers/remoteproc/qcom_common.c      | 89 
>> ++++++++++++++++++++++++++++++-----
>>  drivers/remoteproc/qcom_common.h      | 10 +++-
>>  include/linux/remoteproc/qcom_rproc.h | 20 ++++++--
>>  3 files changed, 99 insertions(+), 20 deletions(-)
>> 
>> diff --git a/drivers/remoteproc/qcom_common.c 
>> b/drivers/remoteproc/qcom_common.c
>> index 60650bc..7cd17be 100644
>> --- a/drivers/remoteproc/qcom_common.c
>> +++ b/drivers/remoteproc/qcom_common.c
>> @@ -15,16 +15,18 @@
>>  #include <linux/rpmsg/qcom_glink.h>
>>  #include <linux/rpmsg/qcom_smd.h>
>>  #include <linux/soc/qcom/mdt_loader.h>
>> +#include <linux/remoteproc/qcom_rproc.h>
> 
> Please maintain alphabetical sort order.
> 
>> 
>>  #include "remoteproc_internal.h"
>>  #include "qcom_common.h"
>> 
>> +#define MAX_NAME_LEN	20
>> +DEFINE_MUTEX(rproc_notif_lock);
> 
> Please rename this qcom_ssr_subsystem_lock
> 
>> +
>>  #define to_glink_subdev(d) container_of(d, struct qcom_rproc_glink, 
>> subdev)
>>  #define to_smd_subdev(d) container_of(d, struct qcom_rproc_subdev, 
>> subdev)
>>  #define to_ssr_subdev(d) container_of(d, struct qcom_rproc_ssr, 
>> subdev)
>> 
>> -static BLOCKING_NOTIFIER_HEAD(ssr_notifiers);
> 
> Move the definition of rproc_notif_info, the new rproc_notif_info list
> head and move the two lines above here as well.
> 
>> -
>>  static int glink_subdev_start(struct rproc_subdev *subdev)
>>  {
>>  	struct qcom_rproc_glink *glink = to_glink_subdev(subdev);
>> @@ -174,39 +176,81 @@ void qcom_remove_smd_subdev(struct rproc *rproc, 
>> struct qcom_rproc_subdev *smd)
>>  }
>>  EXPORT_SYMBOL_GPL(qcom_remove_smd_subdev);
>> 
>> +struct rproc_notif_info *find_notif_info(const char *name)
> 
> Please make this qcom_ssr_get_subsystem(const char *name)
> 
>> +{
>> +	struct rproc_notif_info *info;
>> +
>> +	/* Match in the global rproc_notif_list with name */
>> +	list_for_each_entry(info, &rproc_notif_list, list) {
>> +		if (!strncmp(info->name, name, strlen(name)))
> 
> strncmp(a, b, strlen(b)) is the same thing as strcmp(a, b), unless a is
> shorted than b and not NUL terminated.
> 
>> +			return info;
>> +	}
>> +	return NULL;
> 
> Both callers of this function will if NULL is returned allocate a new
> subsystem object and attach to the list. If you do that here you can
> remove the duplication between these.
> 
>> +}
>> +
>>  /**
>>   * qcom_register_ssr_notifier() - register SSR notification handler
>> + * @name:	pointer to name which will be searched in the global 
>> notif_list
>>   * @nb:		notifier_block to notify for restart notifications
>>   *
>> - * Returns 0 on success, negative errno on failure.
>> + * Returns pointer to srcu notifier head on success, ERR_PTR on 
>> failure.
> 
> This shouldn't mention that the opaque pointer is of a type standard to
> the kernel. Better just say that it returns a "subsystem cookie".
> 
>>   *
>> - * This register the @notify function as handler for restart 
>> notifications. As
>> - * remote processors are stopped this function will be called, with 
>> the SSR
>> - * name passed as a parameter.
>> + * This registers the @nb notifier block as part the notifier chain 
>> for a
>> + * remoteproc associated with @name. The notifier block's callback
>> + * will be invoked when the particular remote processor is stopped.
>>   */
>> -int qcom_register_ssr_notifier(struct notifier_block *nb)
>> +void *qcom_register_ssr_notifier(const char *name, struct 
>> notifier_block *nb)
>>  {
>> -	return blocking_notifier_chain_register(&ssr_notifiers, nb);
>> +	struct rproc_notif_info *info;
>> +
>> +	mutex_lock(&rproc_notif_lock);
>> +	info = find_notif_info(name);
>> +	if (!info) {
>> +		info = kzalloc(sizeof(*info), GFP_KERNEL);
>> +		if (!info) {
>> +			mutex_unlock(&rproc_notif_lock);
>> +			return ERR_PTR(-ENOMEM);
>> +		}
>> +		info->name = kstrndup(name, MAX_NAME_LEN, GFP_KERNEL);
> 
> This is going to be a constant in a lot of cases, so please use
> kstrdup_const(). Also what's the purpose of limiting the length of 
> this?
> 
>> +		srcu_init_notifier_head(&info->notifier_list);
>> +
>> +		/* Add to global notif list */
>> +		INIT_LIST_HEAD(&info->list);
>> +		list_add_tail(&info->list, &rproc_notif_list);
>> +	}
>> +
>> +	srcu_notifier_chain_register(&info->notifier_list, nb);
>> +	mutex_unlock(&rproc_notif_lock);
>> +	return &info->notifier_list;
>>  }
>>  EXPORT_SYMBOL_GPL(qcom_register_ssr_notifier);
>> 
>>  /**
>>   * qcom_unregister_ssr_notifier() - unregister SSR notification 
>> handler
>> + * @notify:	pointer to srcu notifier head
> 
>       @subsystem: subsystem cookie returned from 
> qcom_register_ssr_notifier
> 
>>   * @nb:		notifier_block to unregister
>>   */
>> -void qcom_unregister_ssr_notifier(struct notifier_block *nb)
>> +int qcom_unregister_ssr_notifier(void *notify, struct notifier_block 
>> *nb)
>>  {
>> -	blocking_notifier_chain_unregister(&ssr_notifiers, nb);
>> +	if (!notify)
>> +		return -EINVAL;
> 
> qcom_register_ssr_notifier() will return a valid cookie or a ERR_PTR()
> so if someone passes NULL here they did something wrong during
> development...
> 
> So it's better to just remove this check and give the developer a nice
> callstack directly pointing out their mistake, than forcing them to
> chase where this -EINVAL comes from.
> 
>> +
>> +	return srcu_notifier_chain_unregister(notify, nb);
>>  }
>>  EXPORT_SYMBOL_GPL(qcom_unregister_ssr_notifier);
>> 
>>  static void ssr_notify_unprepare(struct rproc_subdev *subdev)
>>  {
>>  	struct qcom_rproc_ssr *ssr = to_ssr_subdev(subdev);
>> +	struct rproc_notif_data data = {
>> +		.name = ssr->info->name,
>> +		.crashed = false,
>> +	};
>> 
>> -	blocking_notifier_call_chain(&ssr_notifiers, 0, (void *)ssr->name);
>> +	srcu_notifier_call_chain(&ssr->info->notifier_list, 0, &data);
> 
> Did we conclude on why you change blocking to srcu? Can we do it in a
> separate patch?
> 
Since the notifier list needs to be dynamically added for every 
subsystem using srcu
notifier makes sense. I'm not sure if we can use blocking notifier 
dynamically here.
>>  }
>> 
>> +
>>  /**
>>   * qcom_add_ssr_subdev() - register subdevice as restart notification 
>> source
>>   * @rproc:	rproc handle
>> @@ -214,12 +258,30 @@ static void ssr_notify_unprepare(struct 
>> rproc_subdev *subdev)
>>   * @ssr_name:	identifier to use for notifications originating from 
>> @rproc
>>   *
>>   * As the @ssr is registered with the @rproc SSR events will be sent 
>> to all
>> - * registered listeners in the system as the remoteproc is shut down.
>> + * registered listeners for the particular remoteproc when it is 
>> shutdown.
>>   */
>>  void qcom_add_ssr_subdev(struct rproc *rproc, struct qcom_rproc_ssr 
>> *ssr,
>>  			 const char *ssr_name)
>>  {
>> -	ssr->name = ssr_name;
>> +	struct rproc_notif_info *info;
>> +
>> +	mutex_lock(&rproc_notif_lock);
>> +	info = find_notif_info(ssr_name);
>> +	if (!info) {
>> +		info = kzalloc(sizeof(*info), GFP_KERNEL);
>> +		if (!info) {
>> +			mutex_unlock(&rproc_notif_lock);
>> +			return;
>> +		}
>> +		info->name = ssr_name;
>> +		srcu_init_notifier_head(&info->notifier_list);
>> +
>> +		/* Add to global notif_list */
>> +		INIT_LIST_HEAD(&info->list);
>> +		list_add_tail(&info->list, &rproc_notif_list);
>> +	}
>> +	mutex_unlock(&rproc_notif_lock);
>> +	ssr->info = info;
>>  	ssr->subdev.unprepare = ssr_notify_unprepare;
>> 
>>  	rproc_add_subdev(rproc, &ssr->subdev);
>> @@ -233,6 +295,7 @@ void qcom_add_ssr_subdev(struct rproc *rproc, 
>> struct qcom_rproc_ssr *ssr,
>>   */
>>  void qcom_remove_ssr_subdev(struct rproc *rproc, struct 
>> qcom_rproc_ssr *ssr)
>>  {
>> +	ssr->info = NULL;
> 
> Move this after rproc_remove_subdev() and rely on the core for this not
> to race with the ssr_notify_unprepare().
> 
>>  	rproc_remove_subdev(rproc, &ssr->subdev);
>>  }
>>  EXPORT_SYMBOL_GPL(qcom_remove_ssr_subdev);
> 
> It would be nice with a module_exit() that walks the rproc_notif_list
> and free all the elements, if qcom_common.ko is rmmod'ed. Given that
> this is uncommon I wouldn't mind to take that as a separate patch
> though.
> 
Yes i can submit that as a separate patch.
>> diff --git a/drivers/remoteproc/qcom_common.h 
>> b/drivers/remoteproc/qcom_common.h
>> index 58de71e..0c1d288 100644
>> --- a/drivers/remoteproc/qcom_common.h
>> +++ b/drivers/remoteproc/qcom_common.h
>> @@ -24,10 +24,16 @@ struct qcom_rproc_subdev {
>>  	struct qcom_smd_edge *edge;
>>  };
>> 
>> +struct rproc_notif_info {
> 
> Please rename this struct qcom_ssr_subsystem
> 
>> +	const char *name;
>> +	struct srcu_notifier_head notifier_list;
>> +	struct list_head list;
>> +};
>> +static LIST_HEAD(rproc_notif_list);
> 
> Please rename this list qcom_ssr_subsystem_list and as stated above 
> move
> it into qcom_common.c.
> 
> 
> To allow using qcom_ssr_subsystem in the struct below simply forward
> declare it here as:
> 
> struct qcom_ssr_subsystem;
> 
>> +
>>  struct qcom_rproc_ssr {
>>  	struct rproc_subdev subdev;
>> -
>> -	const char *name;
>> +	struct rproc_notif_info *info;
>>  };
>> 
> 
> Regards,
> Bjorn
> 
>>  void qcom_add_glink_subdev(struct rproc *rproc, struct 
>> qcom_rproc_glink *glink);
>> diff --git a/include/linux/remoteproc/qcom_rproc.h 
>> b/include/linux/remoteproc/qcom_rproc.h
>> index fa8e386..3dc65c0 100644
>> --- a/include/linux/remoteproc/qcom_rproc.h
>> +++ b/include/linux/remoteproc/qcom_rproc.h
>> @@ -5,17 +5,27 @@
>> 
>>  #if IS_ENABLED(CONFIG_QCOM_RPROC_COMMON)
>> 
>> -int qcom_register_ssr_notifier(struct notifier_block *nb);
>> -void qcom_unregister_ssr_notifier(struct notifier_block *nb);
>> +struct rproc_notif_data {
>> +	const char *name;
>> +	bool crashed;
>> +};
>> +
>> +void *qcom_register_ssr_notifier(const char *name, struct 
>> notifier_block *nb);
>> +int qcom_unregister_ssr_notifier(void *notify, struct notifier_block 
>> *nb);
>> 
>>  #else
>> 
>> -static inline int qcom_register_ssr_notifier(struct notifier_block 
>> *nb)
>> +static inline void *qcom_register_ssr_notifier(const char *name,
>> +						struct notifier_block *nb)
>>  {
>> -	return 0;
>> +	return NULL;
>>  }
>> 
>> -static inline void qcom_unregister_ssr_notifier(struct notifier_block 
>> *nb) {}
>> +static inline int qcom_unregister_ssr_notifier(void *notify,
>> +						struct notifier_block *nb)
>> +{
>> +	return 0;
>> +}
>> 
>>  #endif
>> 
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project

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