Re: [RFC PATCH 2/5] media: cec-notifier: Get notifier by device and connector name

[Neil Armstrong <narmstrong@baylibre.com>]

On 15/05/2018 08:27, Hans Verkuil wrote:
> Hi Neil,
> 
> Thanks for this patch series!
> 
> Some comments below:
> 
> On 05/15/2018 12:40 AM, Neil Armstrong wrote:
>> In non device-tree world, we can need to get the notifier by the driver
>> name directly and eventually defer probe if not yet created.
>>
>> This patch adds a variant of the get function by using the device name
>> instead and will not create a notifier if not yet created.
>>
>> But the i915 driver exposes at least 2 HDMI connectors, this patch also
>> adds the possibility to add a connector name tied to the notifier device
>> to form a tuple and associate different CEC controllers for each HDMI
>> connectors.
>>
>> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
>> ---
>>  drivers/media/cec/cec-notifier.c | 30 ++++++++++++++++++++++++---
>>  include/media/cec-notifier.h     | 44 ++++++++++++++++++++++++++++++++++++++--
>>  2 files changed, 69 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/media/cec/cec-notifier.c b/drivers/media/cec/cec-notifier.c
>> index 16dffa0..716070a 100644
>> --- a/drivers/media/cec/cec-notifier.c
>> +++ b/drivers/media/cec/cec-notifier.c
>> @@ -21,6 +21,7 @@ struct cec_notifier {
>>  	struct list_head head;
>>  	struct kref kref;
>>  	struct device *dev;
>> +	const char *conn;
>>  	struct cec_adapter *cec_adap;
>>  	void (*callback)(struct cec_adapter *adap, u16 pa);
>>  
>> @@ -30,13 +31,34 @@ struct cec_notifier {
>>  static LIST_HEAD(cec_notifiers);
>>  static DEFINE_MUTEX(cec_notifiers_lock);
>>  
>> -struct cec_notifier *cec_notifier_get(struct device *dev)
>> +struct cec_notifier *cec_notifier_get_byname(const char *name,
>> +					     const char *conn)
>>  {
>>  	struct cec_notifier *n;
>>  
>>  	mutex_lock(&cec_notifiers_lock);
>>  	list_for_each_entry(n, &cec_notifiers, head) {
>> -		if (n->dev == dev) {
>> +		if (!strcmp(dev_name(n->dev), name) &&
>> +		    (!conn || !strcmp(n->conn, conn))) {
>> +			kref_get(&n->kref);
>> +			mutex_unlock(&cec_notifiers_lock);
>> +			return n;
>> +		}
>> +	}
>> +	mutex_unlock(&cec_notifiers_lock);
>> +
>> +	return NULL;
> 
> This doesn't seem right. For one it doesn't act like the other cec_notifier_get*
> functions in that it doesn't make a new notifier if it wasn't found yet in the
> list.
> 
> For another, I think this function shouldn't be here at all. How about calling
> bus_find_device_by_name(), then use cec_notifier_get_conn()?

Yes, it's safer and will keep the original cec_notifier_get() behavior.

> 
>> +}
>> +EXPORT_SYMBOL_GPL(cec_notifier_get_byname);
>> +
>> +struct cec_notifier *cec_notifier_get_conn(struct device *dev, const char *conn)
>> +{
>> +	struct cec_notifier *n;
>> +
>> +	mutex_lock(&cec_notifiers_lock);
>> +	list_for_each_entry(n, &cec_notifiers, head) {
>> +		if (n->dev == dev &&
>> +		    (!conn || !strcmp(n->conn, conn))) {
>>  			kref_get(&n->kref);
>>  			mutex_unlock(&cec_notifiers_lock);
>>  			return n;
>> @@ -46,6 +68,8 @@ struct cec_notifier *cec_notifier_get(struct device *dev)
>>  	if (!n)
>>  		goto unlock;
>>  	n->dev = dev;
>> +	if (conn)
>> +		n->conn = devm_kstrdup(dev, conn, GFP_KERNEL);
> 
> The use of devm_kstrdup worries me. The problem is that when the 'dev' device
> is removed, this memory is also automatically freed. But the notifier might
> still have a reference through the CEC driver, so you end up with a n->conn
> pointer that points to freed memory.
> 
> I think it is better to just use kstrdup and kfree it when the last notifier
> reference is released.

Ok

> 
>>  	n->phys_addr = CEC_PHYS_ADDR_INVALID;
>>  	mutex_init(&n->lock);
>>  	kref_init(&n->kref);
>> @@ -54,7 +78,7 @@ struct cec_notifier *cec_notifier_get(struct device *dev)
>>  	mutex_unlock(&cec_notifiers_lock);
>>  	return n;
>>  }
>> -EXPORT_SYMBOL_GPL(cec_notifier_get);
>> +EXPORT_SYMBOL_GPL(cec_notifier_get_conn);
>>  
>>  static void cec_notifier_release(struct kref *kref)
>>  {
>> diff --git a/include/media/cec-notifier.h b/include/media/cec-notifier.h
>> index cf0add7..70f2974 100644
>> --- a/include/media/cec-notifier.h
>> +++ b/include/media/cec-notifier.h
>> @@ -20,6 +20,37 @@ struct cec_notifier;
>>  #if IS_REACHABLE(CONFIG_CEC_CORE) && IS_ENABLED(CONFIG_CEC_NOTIFIER)
>>  
>>  /**
>> + * cec_notifier_get_byname - find a cec_notifier for the given device name
>> + * and connector tuple.
>> + * @name: device name that sends the events.
>> + * @conn: the connector name from which the event occurs
>> + *
>> + * If a notifier for device @name exists, then increase the refcount and
>> + * return that notifier.
>> + *
>> + * If it doesn't exist, return NULL
>> + */
>> +struct cec_notifier *cec_notifier_get_byname(const char *name,
>> +					     const char *conn);
>> +
>> +/**
>> + * cec_notifier_get_conn - find or create a new cec_notifier for the given
>> + * device and connector tuple.
>> + * @dev: device that sends the events.
>> + * @conn: the connector name from which the event occurs
>> + *
>> + * If a notifier for device @dev already exists, then increase the refcount
>> + * and return that notifier.
>> + *
>> + * If it doesn't exist, then allocate a new notifier struct and return a
>> + * pointer to that new struct.
>> + *
>> + * Return NULL if the memory could not be allocated.
>> + */
>> +struct cec_notifier *cec_notifier_get_conn(struct device *dev,
>> +					   const char *conn);
>> +
>> +/**
>>   * cec_notifier_get - find or create a new cec_notifier for the given device.
>>   * @dev: device that sends the events.
>>   *
>> @@ -31,7 +62,10 @@ struct cec_notifier;
>>   *
>>   * Return NULL if the memory could not be allocated.
>>   */
>> -struct cec_notifier *cec_notifier_get(struct device *dev);
>> +static inline struct cec_notifier *cec_notifier_get(struct device *dev)
>> +{
>> +	return cec_notifier_get_conn(dev, NULL);
>> +}
>>  
>>  /**
>>   * cec_notifier_put - decrease refcount and delete when the refcount reaches 0.
>> @@ -85,12 +119,18 @@ void cec_register_cec_notifier(struct cec_adapter *adap,
>>  			       struct cec_notifier *notifier);
>>  
>>  #else
>> -static inline struct cec_notifier *cec_notifier_get(struct device *dev)
>> +static inline struct cec_notifier *cec_notifier_get_conn(struct device *dev,
>> +							 const char *conn)
>>  {
>>  	/* A non-NULL pointer is expected on success */
>>  	return (struct cec_notifier *)0xdeadfeed;
>>  }
>>  
>> +static inline struct cec_notifier *cec_notifier_get(struct device *dev)
>> +{
>> +	return cec_notifier_get_conn(dev, NULL);
>> +}
>> +
>>  static inline void cec_notifier_put(struct cec_notifier *n)
>>  {
>>  }
>>
> 
> Regards,
> 
> 	Hans
>