Hi Kieran,
Thanks for your feedback.
On 2017-05-03 18:07:47 +0100, Kieran Bingham wrote:
> 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'
Thanks, will fix for next version.
>
> --
> 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
> >
--
Regards,
Niklas Söderlund
