Re: [PATCH v2] driver core: Remove device link creation limitation

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Jul 29, 2019 at 11:50:05PM +0200, Rafael J. Wysocki wrote:
> On Monday, July 29, 2019 5:48:57 PM CEST Dmitry Osipenko wrote:
> > 16.07.2019 18:21, Rafael J. Wysocki пишет:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > Subject: [PATCH] driver core: Remove device link creation limitation
> > > 
> > > If device_link_add() is called for a consumer/supplier pair with an
> > > existing device link between them and the existing link's type is
> > > not in agreement with the flags passed to that function by its
> > > caller, NULL will be returned.  That is seriously inconvenient,
> > > because it forces the callers of device_link_add() to worry about
> > > what others may or may not do even if that is not relevant to them
> > > for any other reasons.
> > > 
> > > It turns out, however, that this limitation can be made go away
> > > relatively easily.
> > > 
> > > The underlying observation is that if DL_FLAG_STATELESS has been
> > > passed to device_link_add() in flags for the given consumer/supplier
> > > pair at least once, calling either device_link_del() or
> > > device_link_remove() to release the link returned by it should work,
> > > but there are no other requirements associated with that flag.  In
> > > turn, if at least one of the callers of device_link_add() for the
> > > given consumer/supplier pair has not passed DL_FLAG_STATELESS to it
> > > in flags, the driver core should track the status of the link and act
> > > on it as appropriate (ie. the link should be treated as "managed").
> > > This means that DL_FLAG_STATELESS needs to be set for managed device
> > > links and it should be valid to call device_link_del() or
> > > device_link_remove() to drop references to them in certain
> > > sutiations.
> > > 
> > > To allow that to happen, introduce a new (internal) device link flag
> > > called DL_FLAG_MANAGED and make device_link_add() set it automatically
> > > whenever DL_FLAG_STATELESS is not passed to it.  Also make it take
> > > additional references to existing device links that were previously
> > > stateless (that is, with DL_FLAG_STATELESS set and DL_FLAG_MANAGED
> > > unset) and will need to be managed going forward and initialize
> > > their status (which has been DL_STATE_NONE so far).
> > > 
> > > Accordingly, when a managed device link is dropped automatically
> > > by the driver core, make it clear DL_FLAG_MANAGED, reset the link's
> > > status back to DL_STATE_NONE and drop the reference to it associated
> > > with DL_FLAG_MANAGED instead of just deleting it right away (to
> > > allow it to stay around in case it still needs to be released
> > > explicitly by someone).
> > > 
> > > With that, since setting DL_FLAG_STATELESS doesn't mean that the
> > > device link in question is not managed any more, replace all of the
> > > status-tracking checks against DL_FLAG_STATELESS with analogous
> > > checks against DL_FLAG_MANAGED and update the documentation to
> > > reflect these changes.
> > > 
> > > While at it, make device_link_add() reject flags that it does not
> > > recognize, including DL_FLAG_MANAGED.
> > > 
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > Reviewed-by: Saravana Kannan <saravanak@google.com>
> > > Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > > ---
> > > 
> > > -> v2:
> > >    * Add a check to device_link_add() to return NULL if unrecognized flags are
> > >      passed to it.
> > >    * Modify kerneldoc comments around DL_FLAG_MANAGED.
> > > 
> > > I've tentatively added the Tested-by tag from Marek, because I don't expect
> > > the changes made between the initial posting and the v2 to make any difference
> > > for him.
> > > 
> > > ---
> > >  Documentation/driver-api/device_link.rst |    4 
> > >  drivers/base/core.c                      |  176 +++++++++++++++++--------------
> > >  drivers/base/power/runtime.c             |    4 
> > >  include/linux/device.h                   |    4 
> > >  4 files changed, 106 insertions(+), 82 deletions(-)
> > > 
> > > Index: linux-pm/drivers/base/core.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/base/core.c
> > > +++ linux-pm/drivers/base/core.c
> > > @@ -124,6 +124,50 @@ static int device_is_dependent(struct de
> > >  	return ret;
> > >  }
> > >  
> > > +static void device_link_init_status(struct device_link *link,
> > > +				    struct device *consumer,
> > > +				    struct device *supplier)
> > > +{
> > > +	switch (supplier->links.status) {
> > > +	case DL_DEV_PROBING:
> > > +		switch (consumer->links.status) {
> > > +		case DL_DEV_PROBING:
> > > +			/*
> > > +			 * A consumer driver can create a link to a supplier
> > > +			 * that has not completed its probing yet as long as it
> > > +			 * knows that the supplier is already functional (for
> > > +			 * example, it has just acquired some resources from the
> > > +			 * supplier).
> > > +			 */
> > > +			link->status = DL_STATE_CONSUMER_PROBE;
> > > +			break;
> > > +		default:
> > > +			link->status = DL_STATE_DORMANT;
> > > +			break;
> > > +		}
> > > +		break;
> > > +	case DL_DEV_DRIVER_BOUND:
> > > +		switch (consumer->links.status) {
> > > +		case DL_DEV_PROBING:
> > > +			link->status = DL_STATE_CONSUMER_PROBE;
> > > +			break;
> > > +		case DL_DEV_DRIVER_BOUND:
> > > +			link->status = DL_STATE_ACTIVE;
> > > +			break;
> > > +		default:
> > > +			link->status = DL_STATE_AVAILABLE;
> > > +			break;
> > > +		}
> > > +		break;
> > > +	case DL_DEV_UNBINDING:
> > > +		link->status = DL_STATE_SUPPLIER_UNBIND;
> > > +		break;
> > > +	default:
> > > +		link->status = DL_STATE_DORMANT;
> > > +		break;
> > > +	}
> > > +}
> > > +
> > >  static int device_reorder_to_tail(struct device *dev, void *not_used)
> > >  {
> > >  	struct device_link *link;
> > > @@ -165,6 +209,10 @@ void device_pm_move_to_tail(struct devic
> > >  	device_links_read_unlock(idx);
> > >  }
> > >  
> > > +#define DL_MANAGED_LINK_FLAGS (DL_FLAG_AUTOREMOVE_CONSUMER | \
> > > +			       DL_FLAG_AUTOREMOVE_SUPPLIER | \
> > > +			       DL_FLAG_AUTOPROBE_CONSUMER)
> > > +
> > >  /**
> > >   * device_link_add - Create a link between two devices.
> > >   * @consumer: Consumer end of the link.
> > > @@ -179,9 +227,9 @@ void device_pm_move_to_tail(struct devic
> > >   * of the link.  If DL_FLAG_PM_RUNTIME is not set, DL_FLAG_RPM_ACTIVE will be
> > >   * ignored.
> > >   *
> > > - * If DL_FLAG_STATELESS is set in @flags, the link is not going to be managed by
> > > - * the driver core and, in particular, the caller of this function is expected
> > > - * to drop the reference to the link acquired by it directly.
> > > + * If DL_FLAG_STATELESS is set in @flags, the caller of this function is
> > > + * expected to release the link returned by it directly with the help of either
> > > + * device_link_del() or device_link_remove().
> > >   *
> > >   * If that flag is not set, however, the caller of this function is handing the
> > >   * management of the link over to the driver core entirely and its return value
> > > @@ -201,9 +249,16 @@ void device_pm_move_to_tail(struct devic
> > >   * be used to request the driver core to automaticall probe for a consmer
> > >   * driver after successfully binding a driver to the supplier device.
> > >   *
> > > - * The combination of DL_FLAG_STATELESS and either DL_FLAG_AUTOREMOVE_CONSUMER
> > > - * or DL_FLAG_AUTOREMOVE_SUPPLIER set in @flags at the same time is invalid and
> > > - * will cause NULL to be returned upfront.
> > > + * The combination of DL_FLAG_STATELESS and one of DL_FLAG_AUTOREMOVE_CONSUMER,
> > > + * DL_FLAG_AUTOREMOVE_SUPPLIER, or DL_FLAG_AUTOPROBE_CONSUMER set in @flags at
> > > + * the same time is invalid and will cause NULL to be returned upfront.
> > > + * However, if a device link between the given @consumer and @supplier pair
> > > + * exists already when this function is called for them, the existing link will
> > > + * be returned regardless of its current type and status (the link's flags may
> > > + * be modified then).  The caller of this function is then expected to treat
> > > + * the link as though it has just been created, so (in particular) if
> > > + * DL_FLAG_STATELESS was passed in @flags, the link needs to be released
> > > + * explicitly when not needed any more (as stated above).
> > >   *
> > >   * A side effect of the link creation is re-ordering of dpm_list and the
> > >   * devices_kset list by moving the consumer device and all devices depending
> > > @@ -220,10 +275,8 @@ struct device_link *device_link_add(stru
> > >  	struct device_link *link;
> > >  
> > >  	if (!consumer || !supplier ||
> > > -	    (flags & DL_FLAG_STATELESS &&
> > > -	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
> > > -		      DL_FLAG_AUTOREMOVE_SUPPLIER |
> > > -		      DL_FLAG_AUTOPROBE_CONSUMER)) ||
> > > +	    (flags & ~(DL_FLAG_STATELESS | DL_MANAGED_LINK_FLAGS)) ||
> > > +	    (flags & DL_FLAG_STATELESS && flags & DL_MANAGED_LINK_FLAGS) ||
> > >  	    (flags & DL_FLAG_AUTOPROBE_CONSUMER &&
> > >  	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
> > >  		      DL_FLAG_AUTOREMOVE_SUPPLIER)))
> > > @@ -236,6 +289,9 @@ struct device_link *device_link_add(stru
> > >  		}
> > >  	}
> > >  
> > > +	if (!(flags & DL_FLAG_STATELESS))
> > > +		flags |= DL_FLAG_MANAGED;
> > > +
> > >  	device_links_write_lock();
> > >  	device_pm_lock();
> > >  
> > > @@ -262,15 +318,6 @@ struct device_link *device_link_add(stru
> > >  		if (link->consumer != consumer)
> > >  			continue;
> > >  
> > > -		/*
> > > -		 * Don't return a stateless link if the caller wants a stateful
> > > -		 * one and vice versa.
> > > -		 */
> > > -		if (WARN_ON((flags & DL_FLAG_STATELESS) != (link->flags & DL_FLAG_STATELESS))) {
> > > -			link = NULL;
> > > -			goto out;
> > > -		}
> > > -
> > >  		if (flags & DL_FLAG_PM_RUNTIME) {
> > >  			if (!(link->flags & DL_FLAG_PM_RUNTIME)) {
> > >  				pm_runtime_new_link(consumer);
> > > @@ -281,6 +328,7 @@ struct device_link *device_link_add(stru
> > >  		}
> > >  
> > >  		if (flags & DL_FLAG_STATELESS) {
> > > +			link->flags |= DL_FLAG_STATELESS;
> > >  			kref_get(&link->kref);
> > >  			goto out;
> > >  		}
> > > @@ -299,6 +347,11 @@ struct device_link *device_link_add(stru
> > >  			link->flags &= ~(DL_FLAG_AUTOREMOVE_CONSUMER |
> > >  					 DL_FLAG_AUTOREMOVE_SUPPLIER);
> > >  		}
> > > +		if (!(link->flags & DL_FLAG_MANAGED)) {
> > > +			kref_get(&link->kref);
> > > +			link->flags |= DL_FLAG_MANAGED;
> > > +			device_link_init_status(link, consumer, supplier);
> > > +		}
> > >  		goto out;
> > >  	}
> > >  
> > > @@ -325,48 +378,10 @@ struct device_link *device_link_add(stru
> > >  	kref_init(&link->kref);
> > >  
> > >  	/* Determine the initial link state. */
> > > -	if (flags & DL_FLAG_STATELESS) {
> > > +	if (flags & DL_FLAG_STATELESS)
> > >  		link->status = DL_STATE_NONE;
> > > -	} else {
> > > -		switch (supplier->links.status) {
> > > -		case DL_DEV_PROBING:
> > > -			switch (consumer->links.status) {
> > > -			case DL_DEV_PROBING:
> > > -				/*
> > > -				 * A consumer driver can create a link to a
> > > -				 * supplier that has not completed its probing
> > > -				 * yet as long as it knows that the supplier is
> > > -				 * already functional (for example, it has just
> > > -				 * acquired some resources from the supplier).
> > > -				 */
> > > -				link->status = DL_STATE_CONSUMER_PROBE;
> > > -				break;
> > > -			default:
> > > -				link->status = DL_STATE_DORMANT;
> > > -				break;
> > > -			}
> > > -			break;
> > > -		case DL_DEV_DRIVER_BOUND:
> > > -			switch (consumer->links.status) {
> > > -			case DL_DEV_PROBING:
> > > -				link->status = DL_STATE_CONSUMER_PROBE;
> > > -				break;
> > > -			case DL_DEV_DRIVER_BOUND:
> > > -				link->status = DL_STATE_ACTIVE;
> > > -				break;
> > > -			default:
> > > -				link->status = DL_STATE_AVAILABLE;
> > > -				break;
> > > -			}
> > > -			break;
> > > -		case DL_DEV_UNBINDING:
> > > -			link->status = DL_STATE_SUPPLIER_UNBIND;
> > > -			break;
> > > -		default:
> > > -			link->status = DL_STATE_DORMANT;
> > > -			break;
> > > -		}
> > > -	}
> > > +	else
> > > +		device_link_init_status(link, consumer, supplier);
> > >  
> > >  	/*
> > >  	 * Some callers expect the link creation during consumer driver probe to
> > > @@ -528,7 +543,7 @@ static void device_links_missing_supplie
> > >   * mark the link as "consumer probe in progress" to make the supplier removal
> > >   * wait for us to complete (or bad things may happen).
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  int device_links_check_suppliers(struct device *dev)
> > >  {
> > > @@ -538,7 +553,7 @@ int device_links_check_suppliers(struct
> > >  	device_links_write_lock();
> > >  
> > >  	list_for_each_entry(link, &dev->links.suppliers, c_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		if (link->status != DL_STATE_AVAILABLE) {
> > > @@ -563,7 +578,7 @@ int device_links_check_suppliers(struct
> > >   *
> > >   * Also change the status of @dev's links to suppliers to "active".
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  void device_links_driver_bound(struct device *dev)
> > >  {
> > > @@ -572,7 +587,7 @@ void device_links_driver_bound(struct de
> > >  	device_links_write_lock();
> > >  
> > >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		/*
> > > @@ -593,7 +608,7 @@ void device_links_driver_bound(struct de
> > >  	}
> > >  
> > >  	list_for_each_entry(link, &dev->links.suppliers, c_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		WARN_ON(link->status != DL_STATE_CONSUMER_PROBE);
> > > @@ -605,6 +620,13 @@ void device_links_driver_bound(struct de
> > >  	device_links_write_unlock();
> > >  }
> > >  
> > > +static void device_link_drop_managed(struct device_link *link)
> > > +{
> > > +	link->flags &= ~DL_FLAG_MANAGED;
> > > +	WRITE_ONCE(link->status, DL_STATE_NONE);
> > > +	kref_put(&link->kref, __device_link_del);
> > > +}
> > > +
> > >  /**
> > >   * __device_links_no_driver - Update links of a device without a driver.
> > >   * @dev: Device without a drvier.
> > > @@ -615,18 +637,18 @@ void device_links_driver_bound(struct de
> > >   * unless they already are in the "supplier unbind in progress" state in which
> > >   * case they need not be updated.
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  static void __device_links_no_driver(struct device *dev)
> > >  {
> > >  	struct device_link *link, *ln;
> > >  
> > >  	list_for_each_entry_safe_reverse(link, ln, &dev->links.suppliers, c_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER)
> > > -			__device_link_del(&link->kref);
> > > +			device_link_drop_managed(link);
> > >  		else if (link->status == DL_STATE_CONSUMER_PROBE ||
> > >  			 link->status == DL_STATE_ACTIVE)
> > >  			WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
> > > @@ -643,7 +665,7 @@ static void __device_links_no_driver(str
> > >   * %__device_links_no_driver() to update links to suppliers for it as
> > >   * appropriate.
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  void device_links_no_driver(struct device *dev)
> > >  {
> > > @@ -652,7 +674,7 @@ void device_links_no_driver(struct devic
> > >  	device_links_write_lock();
> > >  
> > >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		/*
> > > @@ -680,7 +702,7 @@ void device_links_no_driver(struct devic
> > >   * invoke %__device_links_no_driver() to update links to suppliers for it as
> > >   * appropriate.
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  void device_links_driver_cleanup(struct device *dev)
> > >  {
> > > @@ -689,7 +711,7 @@ void device_links_driver_cleanup(struct
> > >  	device_links_write_lock();
> > >  
> > >  	list_for_each_entry_safe(link, ln, &dev->links.consumers, s_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		WARN_ON(link->flags & DL_FLAG_AUTOREMOVE_CONSUMER);
> > > @@ -702,7 +724,7 @@ void device_links_driver_cleanup(struct
> > >  		 */
> > >  		if (link->status == DL_STATE_SUPPLIER_UNBIND &&
> > >  		    link->flags & DL_FLAG_AUTOREMOVE_SUPPLIER)
> > > -			__device_link_del(&link->kref);
> > > +			device_link_drop_managed(link);
> > >  
> > >  		WRITE_ONCE(link->status, DL_STATE_DORMANT);
> > >  	}
> > > @@ -724,7 +746,7 @@ void device_links_driver_cleanup(struct
> > >   *
> > >   * Return 'false' if there are no probing or active consumers.
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  bool device_links_busy(struct device *dev)
> > >  {
> > > @@ -734,7 +756,7 @@ bool device_links_busy(struct device *de
> > >  	device_links_write_lock();
> > >  
> > >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		if (link->status == DL_STATE_CONSUMER_PROBE
> > > @@ -764,7 +786,7 @@ bool device_links_busy(struct device *de
> > >   * driver to unbind and start over (the consumer will not re-probe as we have
> > >   * changed the state of the link already).
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links without the DL_FLAG_MANAGED flag set are ignored.
> > >   */
> > >  void device_links_unbind_consumers(struct device *dev)
> > >  {
> > > @@ -776,7 +798,7 @@ void device_links_unbind_consumers(struc
> > >  	list_for_each_entry(link, &dev->links.consumers, s_node) {
> > >  		enum device_link_state status;
> > >  
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		status = link->status;
> > > Index: linux-pm/drivers/base/power/runtime.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/base/power/runtime.c
> > > +++ linux-pm/drivers/base/power/runtime.c
> > > @@ -1624,7 +1624,7 @@ void pm_runtime_remove(struct device *de
> > >   * runtime PM references to the device, drop the usage counter of the device
> > >   * (as many times as needed).
> > >   *
> > > - * Links with the DL_FLAG_STATELESS flag set are ignored.
> > > + * Links with the DL_FLAG_MANAGED flag unset are ignored.
> > >   *
> > >   * Since the device is guaranteed to be runtime-active at the point this is
> > >   * called, nothing else needs to be done here.
> > > @@ -1641,7 +1641,7 @@ void pm_runtime_clean_up_links(struct de
> > >  	idx = device_links_read_lock();
> > >  
> > >  	list_for_each_entry_rcu(link, &dev->links.consumers, s_node) {
> > > -		if (link->flags & DL_FLAG_STATELESS)
> > > +		if (!(link->flags & DL_FLAG_MANAGED))
> > >  			continue;
> > >  
> > >  		while (refcount_dec_not_one(&link->rpm_active))
> > > Index: linux-pm/include/linux/device.h
> > > ===================================================================
> > > --- linux-pm.orig/include/linux/device.h
> > > +++ linux-pm/include/linux/device.h
> > > @@ -829,12 +829,13 @@ enum device_link_state {
> > >  /*
> > >   * Device link flags.
> > >   *
> > > - * STATELESS: The core won't track the presence of supplier/consumer drivers.
> > > + * STATELESS: The core will not remove this link automatically.
> > >   * AUTOREMOVE_CONSUMER: Remove the link automatically on consumer driver unbind.
> > >   * PM_RUNTIME: If set, the runtime PM framework will use this link.
> > >   * RPM_ACTIVE: Run pm_runtime_get_sync() on the supplier during link creation.
> > >   * AUTOREMOVE_SUPPLIER: Remove the link automatically on supplier driver unbind.
> > >   * AUTOPROBE_CONSUMER: Probe consumer driver automatically after supplier binds.
> > > + * MANAGED: The core tracks presence of supplier/consumer drivers (internal).
> > >   */
> > >  #define DL_FLAG_STATELESS		BIT(0)
> > >  #define DL_FLAG_AUTOREMOVE_CONSUMER	BIT(1)
> > > @@ -842,6 +843,7 @@ enum device_link_state {
> > >  #define DL_FLAG_RPM_ACTIVE		BIT(3)
> > >  #define DL_FLAG_AUTOREMOVE_SUPPLIER	BIT(4)
> > >  #define DL_FLAG_AUTOPROBE_CONSUMER	BIT(5)
> > > +#define DL_FLAG_MANAGED			BIT(6)
> > >  
> > >  /**
> > >   * struct device_link - Device link representation.
> > > Index: linux-pm/Documentation/driver-api/device_link.rst
> > > ===================================================================
> > > --- linux-pm.orig/Documentation/driver-api/device_link.rst
> > > +++ linux-pm/Documentation/driver-api/device_link.rst
> > > @@ -78,8 +78,8 @@ typically deleted in its ``->remove`` ca
> > >  driver is compiled as a module, the device link is added on module load and
> > >  orderly deleted on unload.  The same restrictions that apply to device link
> > >  addition (e.g. exclusion of a parallel suspend/resume transition) apply equally
> > > -to deletion.  Device links with ``DL_FLAG_STATELESS`` unset (i.e. managed
> > > -device links) are deleted automatically by the driver core.
> > > +to deletion.  Device links managed by the driver core are deleted automatically
> > > +by it.
> > >  
> > >  Several flags may be specified on device link addition, two of which
> > >  have already been mentioned above:  ``DL_FLAG_STATELESS`` to express that no
> > > 
> > > 
> > > 
> > > 
> > 
> > Hello Rafael,
> > 
> > This patch breaks NVIDIA Tegra DRM driver, which fails to probe now
> > using the recent linux-next.
> > 
> > 	tegra-dc 54240000.dc: failed to link controllers
> > 
> 
> Thanks for the report and sorry for the breakage!
> 
> My bad, obviously DL_FLAG_PM_RUNTIME must be accepted by device_link_add(),
> as well as DL_FLAG_RPM_ACTIVE.
> 
> Please test the appended patch and let me know if it helps.
> 
> Greg, in case this is confirmed to fix the issue, do you want me to post it as a
> separate patch, or would you prefer a v3 of the $subject one?

Separate patch please, I can't rebase my tree.

thanks,

greg k-h