Hi Niklas,
Small thing to ponder discovered below:
On 27/04/17 23:30, Niklas Söderlund wrote:
> When registered() of v4l2_subdev_internal_ops is called the subdevice
> have access to the master devices v4l2_dev and it's called with the
> async frameworks list_lock held. In this context the subdevice can
> register its own notifiers to allow for incremental discovery of
> subdevices.
>
> The master device registers the subdevices closest to itself in its
> notifier while the subdevice(s) themself register notifiers for there
> closest neighboring devices when they are registered. Using this
> incremental approach two problems can be solved.
>
> 1. The master device no longer have to care how many subdevices exist in
> the pipeline. It only needs to care about its closest subdevice and
> arbitrary long pipelines can be created without having to adapt the
> master device for each case.
>
> 2. Subdevices which are represented as a single DT node but register
> more then one subdevice can use this to further the pipeline
> discovery. Since the subdevice driver is the only one who knows which
> of its subdevices is linked with which subdevice of a neighboring DT
> node.
>
> To enable subdevices to register/unregister notifiers from the
> registered()/unregistered() callback v4l2_async_subnotifier_register()
> and v4l2_async_subnotifier_unregister() are added. These new notifier
> register functions are similar to the master device equivalent functions
> but run without taking the v4l2-async list_lock which already are held
> when he registered()/unregistered() callbacks are called.
>
> Signed-off-by: Niklas Söderlund <niklas.soderlund+rene...@ragnatech.se>
> ---
> drivers/media/v4l2-core/v4l2-async.c | 91
> +++++++++++++++++++++++++++++-------
> include/media/v4l2-async.h | 22 +++++++++
> 2 files changed, 95 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-async.c
> b/drivers/media/v4l2-core/v4l2-async.c
> index 96cc733f35ef72b0..d4a676a2935eb058 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -136,12 +136,13 @@ static void v4l2_async_cleanup(struct v4l2_subdev *sd)
> sd->dev = NULL;
> }
>
> -int v4l2_async_notifier_register(struct v4l2_device *v4l2_dev,
> - struct v4l2_async_notifier *notifier)
> +static int v4l2_async_do_notifier_register(struct v4l2_device *v4l2_dev,
> + struct v4l2_async_notifier *notifier,
> + bool subnotifier)
> {
> struct v4l2_subdev *sd, *tmp;
> struct v4l2_async_subdev *asd;
> - int i;
> + int found, i;
>
> if (!notifier->num_subdevs || notifier->num_subdevs > V4L2_MAX_SUBDEVS)
> return -EINVAL;
> @@ -168,32 +169,69 @@ int v4l2_async_notifier_register(struct v4l2_device
> *v4l2_dev,
> list_add_tail(&asd->list, ¬ifier->waiting);
> }
>
> - mutex_lock(&list_lock);
> + if (!subnotifier)
> + mutex_lock(&list_lock);
> +
> + /*
> + * This function can be called recursively so the list
> + * might be modified in a recursive call. Start from the
> + * top of the list each iteration.
> + */
> + found = 1;
> + while (found) {
> + found = 0;
>
> - list_for_each_entry_safe(sd, tmp, &subdev_list, async_list) {
> - int ret;
> + list_for_each_entry_safe(sd, tmp, &subdev_list, async_list) {
> + int ret;
>
> - asd = v4l2_async_belongs(notifier, sd);
> - if (!asd)
> - continue;
> + asd = v4l2_async_belongs(notifier, sd);
> + if (!asd)
> + continue;
>
> - ret = v4l2_async_test_notify(notifier, sd, asd);
> - if (ret < 0) {
> - mutex_unlock(&list_lock);
> - return ret;
> + ret = v4l2_async_test_notify(notifier, sd, asd);
> + if (ret < 0) {
> + if (!subnotifier)
> + mutex_unlock(&list_lock);
> + return ret;
> + }
> +
> + found = 1;
> + break;
> }
> }
>
> /* Keep also completed notifiers on the list */
> list_add(¬ifier->list, ¬ifier_list);
>
> - mutex_unlock(&list_lock);
> + if (!subnotifier)
> + mutex_unlock(&list_lock);
>
> return 0;
> }
> +
> +int v4l2_async_subnotifier_register(struct v4l2_subdev *sd,
> + struct v4l2_async_notifier *notifier)
> +{
> + if (!sd->v4l2_dev) {
> + dev_err(sd->dev ? sd->dev : NULL,
Just came across this, and it seems a bit 'extraneous'
'If sd->dev is not null, use sd->dev, otherwise use NULL'
--
KB
> + "Can't register subnotifier for without v4l2_dev\n");
> + return -EINVAL;
> + }
> +
> + return v4l2_async_do_notifier_register(sd->v4l2_dev, notifier, true);
> +}
> +EXPORT_SYMBOL(v4l2_async_subnotifier_register);
> +
> +int v4l2_async_notifier_register(struct v4l2_device *v4l2_dev,
> + struct v4l2_async_notifier *notifier)
> +{
> + return v4l2_async_do_notifier_register(v4l2_dev, notifier, false);
> +}
> EXPORT_SYMBOL(v4l2_async_notifier_register);
>
> -void v4l2_async_notifier_unregister(struct v4l2_async_notifier *notifier)
> +static void
> +v4l2_async_do_notifier_unregister(struct v4l2_async_notifier *notifier,
> + bool subnotifier)
> {
> struct v4l2_subdev *sd, *tmp;
> unsigned int notif_n_subdev = notifier->num_subdevs;
> @@ -210,7 +248,8 @@ void v4l2_async_notifier_unregister(struct
> v4l2_async_notifier *notifier)
> "Failed to allocate device cache!\n");
> }
>
> - mutex_lock(&list_lock);
> + if (!subnotifier)
> + mutex_lock(&list_lock);
>
> list_del(¬ifier->list);
>
> @@ -237,15 +276,20 @@ void v4l2_async_notifier_unregister(struct
> v4l2_async_notifier *notifier)
> put_device(d);
> }
>
> - mutex_unlock(&list_lock);
> + if (!subnotifier)
> + mutex_unlock(&list_lock);
>
> /*
> * Call device_attach() to reprobe devices
> *
> * NOTE: If dev allocation fails, i is 0, and the whole loop won't be
> * executed.
> + * TODO: If we are unregistering a subdevice notifier we can't reprobe
> + * since the lock_list is held by the master device and attaching that
> + * device would call v4l2_async_register_subdev() and end in a deadlock
> + * on list_lock.
> */
> - while (i--) {
> + while (i-- && !subnotifier) {
> struct device *d = dev[i];
>
> if (d && device_attach(d) < 0) {
> @@ -269,6 +313,17 @@ void v4l2_async_notifier_unregister(struct
> v4l2_async_notifier *notifier)
> * upon notifier registration.
> */
> }
> +
> +void v4l2_async_subnotifier_unregister(struct v4l2_async_notifier *notifier)
> +{
> + v4l2_async_do_notifier_unregister(notifier, true);
> +}
> +EXPORT_SYMBOL(v4l2_async_subnotifier_unregister);
> +
> +void v4l2_async_notifier_unregister(struct v4l2_async_notifier *notifier)
> +{
> + v4l2_async_do_notifier_unregister(notifier, false);
> +}
> EXPORT_SYMBOL(v4l2_async_notifier_unregister);
>
> int v4l2_async_register_subdev(struct v4l2_subdev *sd)
> diff --git a/include/media/v4l2-async.h b/include/media/v4l2-async.h
> index 8e2a236a4d039df6..dee070be59f211bd 100644
> --- a/include/media/v4l2-async.h
> +++ b/include/media/v4l2-async.h
> @@ -105,6 +105,18 @@ struct v4l2_async_notifier {
> };
>
> /**
> + * v4l2_async_notifier_register - registers a subdevice asynchronous
> subnotifier
> + *
> + * @sd: pointer to &struct v4l2_subdev
> + * @notifier: pointer to &struct v4l2_async_notifier
> + *
> + * This function assumes the async list_lock is already locked, allowing
> + * it to be used from struct v4l2_subdev_internal_ops registered() callback.
> + */
> +int v4l2_async_subnotifier_register(struct v4l2_subdev *sd,
> + struct v4l2_async_notifier *notifier);
> +
> +/**
> * v4l2_async_notifier_register - registers a subdevice asynchronous notifier
> *
> * @v4l2_dev: pointer to &struct v4l2_device
> @@ -114,6 +126,16 @@ int v4l2_async_notifier_register(struct v4l2_device
> *v4l2_dev,
> struct v4l2_async_notifier *notifier);
>
> /**
> + * v4l2_async_subnotifier_unregister - unregisters a asynchronous subnotifier
> + *
> + * @notifier: pointer to &struct v4l2_async_notifier
> + *
> + * This function assumes the async list_lock is already locked, allowing
> + * it to be used from struct v4l2_subdev_internal_ops unregistered()
> callback.
> + */
> +void v4l2_async_subnotifier_unregister(struct v4l2_async_notifier *notifier);
> +
> +/**
> * v4l2_async_notifier_unregister - unregisters a subdevice asynchronous
> notifier
> *
> * @notifier: pointer to &struct v4l2_async_notifier
>
