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

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